Overview of cryoglobulins and cryoglobulinemia

INTRODUCTION — Precipitation of blood proteins at temperatures lower than 37°C is referred to as cryoprecipitation. Two major types of cryoprecipitates are recognized. Cryoglobulin is present when proteins precipitate from an individual's serum and plasma, and cryofibrinogen refers to the precipitate from plasma only [1]. Cryoglobulins are composed of either immunoglobulins (Igs) or a mixture of Igs and complement components.

The diagnosis of a cryoglobulinemia syndrome should be suspected in patients presenting with arthralgia, purpura, skin ulcers, glomerulonephritis, and peripheral neuropathy. The index of suspicion for cryoglobulinemia should be raised further if these occur in the setting of a chronic viral hepatitis (especially hepatitis C virus [HCV]), a monoclonal gammopathy (eg, multiple myeloma; Waldenström macroglobulinemia; monoclonal gammopathy of undetermined significance [MGUS], which then turns to monoclonal gammopathy of clinical significance [MGCS]), monoclonal gammopathies of renal significance, or connective tissue disease (eg, systemic lupus erythematosus [SLE], Sjögren's syndrome).

The nature of cryoglobulins, an overview of the clinical syndromes associated with them (cryoglobulinemia, cryoglobulinemic vasculitis), their pathogenesis, associated disorders, and prognosis are the subjects of this topic review. Treatment of cryoglobulinemia due to plasma cell disorders (monoclonal cryoglobulin) and the clinical manifestations, diagnosis, and treatment of the mixed cryoglobulinemia syndromes, such as those associated with hepatitis C infection, are presented separately. (See "Treatment and prognosis of Waldenström macroglobulinemia" and "Mixed cryoglobulinemia syndrome: Clinical manifestations and diagnosis" and "Mixed cryoglobulinemia syndrome: Treatment and prognosis".)

The clinical manifestations of cryofibrinogenemia and disorders associated with the presence of circulating cryofibrinogen are discussed separately. (See "Disorders of fibrinogen", section on 'Cryofibrinogenemia'.)

TERMINOLOGY

●Cryoglobulin – Cryoglobulins are Igs in the serum that precipitate in vitro at temperatures below 37°C and redissolve on rewarming. The appearance of precipitated cryoglobulin is illustrated in the picture (picture 1).

●Cryoglobulinemia – Cryoglobulinemia refers to the presence of cryoglobulin in a patient's serum. This term is sometimes used interchangeably with cryoglobulinemic vasculitis (or cryoglobulinemia syndrome).

●Cryoglobulinemic vasculitis – Cryoglobulinemic vasculitis (or cryoglobulinemia syndrome) refers to a systemic inflammatory syndrome that generally involves small-to-medium vessel vasculitis due to cryoglobulin-containing immune complexes. This term is generally used to distinguish the asymptomatic presence of cryoglobulins from the clinically apparent disorder with end-organ damage caused by cryoglobulins precipitating in small- to medium-sized blood vessels.

●Mixed cryoglobulinemia – Mixed cryoglobulinemia refers to cryoglobulins that contain more than one immunoglobulin component (for example, IgM rheumatoid factor [RF] and polyclonal IgG). Mixed cryoglobulinemia may be primary or idiopathic cryoglobulinemia, as well as cryoglobulinemia associated with autoimmune diseases, malignancy, or infection. Type II and III mixed cryoglobulinemias correspond to either a monoclonal Ig with polyclonal Igs or polyclonal Igs, respectively. The distinction of these subtypes is meaningful because underlying diseases vary according to each subtype. Mixed cryoglobulinemia syndrome can be caused by either type II or III cryoglobulins, the characteristics of which are described below. (See "Mixed cryoglobulinemia syndrome: Clinical manifestations and diagnosis" and 'Mixed cryoglobulinemia (types II/III)' below.)

●Essential mixed cryoglobulinemia – Essential mixed cryoglobulinemia was the traditional term for what was thought to be idiopathic vasculitis caused by circulating cryoglobulins that contain both a polyclonal IgG and an IgM RF directed against the IgG, which are called mixed cryoglobulins. It was later discovered that in most patients, this disorder is associated with chronic hepatitis C virus (HCV) infection. Therefore, this term currently refers to the very small percentage of patients with mixed cryoglobulinemic vasculitis in the absence of underlying disease.

●Hyperviscosity syndrome – Hyperviscosity syndrome may be present with cryoglobulinemia due to hematologic malignancies and monoclonal Igs (mainly type I cryoglobulinemia). (See "Epidemiology, pathogenesis, clinical manifestations, and diagnosis of Waldenström macroglobulinemia", section on 'Hyperviscosity syndrome'.)

●Meltzer's triad – Meltzer's triad refers to the clinical triad of palpable purpura, arthralgia, and weakness. It is generally seen with the mixed cryoglobulinemia syndrome.

●Immune complex – The multimolecular combination of antibodies bound to their target antigens are referred to as immune complexes. They may be present in blood as circulating immune complexes or present in tissues and organs.

CLASSIFICATION — The Brouet classification criteria is the most commonly used system that classifies cryoglobulinemia into three different subgroups based on their Ig composition [2]. These classification criteria are also useful in that the subgroups partly correlate with pathogenicity and clinical manifestations.

Type I — In type I cryoglobulinemia, the cryoglobulins are monoclonal Igs, typically IgG or IgM, and less commonly IgA or free Ig light chains. Type I cryoglobulinemia develops in the setting of protein-secreting monoclonal gammopathies such as a monoclonal gammopathy of undetermined significance (MGUS), which then turns to monoclonal gammopathy of clinical significance (MGCS) or a B-cell lineage malignancy (eg, multiple myeloma, Waldenström macroglobulinemia, or chronic lymphocytic leukemia). (See "Epidemiology, pathogenesis, clinical manifestations, and diagnosis of Waldenström macroglobulinemia" and "Multiple myeloma: Clinical features, laboratory manifestations, and diagnosis".)

Type II and III cryoglobulins are mixed cryoglobulins, meaning that, unlike type I cryoglobulins, their constituent Ig is not a single monoclonal Ig.

Type II — In type II cryoglobulinemia, the cryoglobulins are composed of a mixture of a monoclonal IgM (or IgG or IgA) with rheumatoid factor (RF) activity and polyclonal Ig. Type II cryoglobulins are often associated with persistent viral infections, particularly hepatitis C virus (HCV) infection, and are associated with the mixed cryoglobulinemia syndrome [3]. Other clinical associations with type II cryoglobulinemia include autoimmune diseases (mainly systemic lupus erythematosus [SLE] and Sjögren's syndrome), lymphoproliferative disorders, and less frequently other infections such as hepatitis B virus (HBV) and human immunodeficiency virus (HIV). In approximately 10 percent of cases, there is no identifiable disease association and the cryoglobulinemia is called "essential." (See "Mixed cryoglobulinemia syndrome: Clinical manifestations and diagnosis".)

Type III — In type III cryoglobulinemia, the cryoglobulins are composed of a mixture of polyclonal IgG (all isotypes) and polyclonal IgM. These cases are often secondary to autoimmune disorders, but can also be associated with infections (mainly HCV).

While generally useful, this schema does not account for cryoglobulins that possess atypical characteristics, such as oligoclonal IgM components with or without trace polyclonal Ig responses, often referred to as type II-III [4,5] or biclonal cryoglobulins [6,7]. Many speculate that such phenomena reflect an intermediate stage of transition between type II and III, akin to the malignant transformation of MGUS to multiple myeloma or other lymphoproliferative disorders [8], but a direct pathogenic link has not been clearly demonstrated. (See "Clinical course and management of monoclonal gammopathy of undetermined significance".)

In addition to classification by the Ig constituents of the cryoglobulin, cryoglobulinemia syndromes are often classified as idiopathic or secondary, based upon the presence of underlying diseases, particularly chronic HCV infection or connective tissue diseases [9].

At the same time, the clinical features of both idiopathic and secondary mixed cryoglobulinemia overlap somewhat, with respect to Brouet subtype and organ involvement, making most distinctions among cryoglobulin syndromes somewhat difficult to interpret consistently.

EPIDEMIOLOGY — The prevalence of clinically significant cryoglobulinemia has been estimated at approximately 1 in 100,000. However, detectable levels of circulating cryoglobulins, without clinical manifestations of vasculitis, have been seen in a significant proportion of patients with chronic infections and/or inflammation: 15 to 20 percent in HIV infection, 15 to 25 percent in connective tissue diseases, 40 to 65 percent in hepatitis C-infected individuals, and as high as 64 percent in HIV and hepatitis C coinfection [10-14]. The proportion of patients with a type I cryoglobulin varies substantially among case series but accounts for approximately 5 to 25 percent of cases.

ETIOPATHOGENESIS — Since minute levels of cryoglobulin may be detectable in the serum of healthy persons, many researchers have speculated that they reflect the ongoing presence of endogenous immune complexes to be cleared from the circulation by Igs with rheumatoid factor (RF) activity [2,15]. In such a scenario, pathogenic cryoglobulin responses would result from several factors, including:

●Chronic immune stimulation and/or lymphoproliferation, resulting in the production of higher concentrations of mono-, oligo-, or polyclonal immunoglobulins that can form cryoglobulins

●Enhanced immune complex (antigen-antibody complex) formation

●Defective and/or insufficient clearance of the resulting immune complexes, which accumulate and mediate disease

Cryoglobulin pathogenesis may depend upon a poorly understood interaction between a polygenic host predisposition and environmental triggers. Major histocompatibility complex (MHC) associations, for instance, have been extensively investigated in hepatitis C virus (HCV)-associated mixed cryoglobulinemia [16]. A genome-wide significant association with cryoglobulin-related vasculitis was identified with single nucleotide polymorphisms (SNPs) near NOTCH4 and MHC class II genes [17]. Significantly elevated levels of inflammatory cytokines, such as interleukin (IL)-1-beta, IL-6, and tumor necrosis factor (TNF)-alpha, have been observed, suggesting a particular role for cryoglobulin-induced inflammation in disease pathogenesis [18].

Although HIV and HCV coinfection are relatively common, the combination of the two viral agents appears to have variable effect upon the prevalence of cryoglobulin or symptomatic cryoglobulinemia syndromes [19]. Other infectious agents proven to have an association with cryoglobulinemia include hepatitis B, cytomegalovirus, Epstein-Barr virus, and human parvovirus B19 [20].

●Type I cryoglobulins – Type I cryoglobulinemia causes hyperviscosity that results from high levels of monoclonal cryoglobulins due to an underlying lymphoproliferative disorder. These Igs form cold-induced precipitates that induce a microthrombotic process within small size vessels. In vivo, such aggregates may physically obstruct vessels and rarely mediate inflammatory vasculitis via immune complex deposition [21], as suggested by studies of human cryoglobulins in animal models [22]. For many cryoglobulins, aggregation and pathogenicity appear to depend upon antibody-specific conditions of temperature, pH, Ig concentration, and weak noncovalent factors [23].

●Types II and III cryoglobulins – The mixed cryoglobulins (types II and III) generally result in two-thirds of cases from connective tissue diseases, such as systemic lupus erythematosus (SLE) or, more rarely, Sjögren's syndrome [24], whereas in one-third, they are associated with chronic HCV infection [25]; other viral infections, such as hepatitis B virus (HBV) or HIV; and lymphoproliferative disorders. Many of these disease states share B-cell hyperactivation and/or hyperproliferation [14,26], which seem to predispose to the selective expansion of cryoglobulin-producing B-cell clone(s) [27], but a precise ontology of pathogenic cryoglobulins in mixed cryoglobulinemia has not been delineated. This paradigm of pathogenesis has been most intensively studied for chronic HCV infection, in which B-cell hyperactivation may result upon direct infection via the cell surface protein CD81 [28]; via chronic, antigen-nonspecific stimulation by macromolecular serum complexes containing HCV, including HCV-IgG and HCV-lipoprotein [29,30]; or via an HCV antigen-specific mechanism [31], resulting in expansion of specific B-cell clones [32,33]. HCV particles are often found in such patients' serum cryoglobulin complexes, but, at the same time, cryoglobulin development in hepatitis C infection does not directly require the HCV virion or its components [34]. In this sense, cryoglobulin development may, in fact, reflect a normal, expected response to regulate immune complexes in states of chronic immune activation.

Among patients with HCV infection, the number of circulating T cells with surface markers compatible with a suppressor phenotype is a feature that differs between patients with cryoglobulinemic vasculitis and those with asymptomatic cryoglobulinemia. This was illustrated in a study that compared the percentage of regulatory T cells in 69 patients with HCV infection who had symptomatic cryoglobulinemia with others with asymptomatic HCV infection [35]. The mean levels of regulatory T cells were significantly lower in those with symptomatic HCV-associated cryoglobulinemia than asymptomatic subjects (2.6 versus 7.4 percent, respectively). Two clinical trials confirm the major role of regulatory T cells in HCV-associated cryoglobulinemia, showing a significant increase of these cells after antivirals or low-dose IL-2 correlates with less clinical activity of the vasculitis [36,37].

●Aggregation – The molecular characteristics of cryoglobulins similarly vary depending upon the underlying disease state. Most commonly, type II cryoglobulins contain germline autoantibodies with RF activity, suggesting an antigen-independent, hyperproliferative etiology [29,38]. Nevertheless, non-RF cryoglobulins have been described, mostly in type I cryoglobulinemia, in which cryoprecipitability seems to be mediated by other characteristics of the Ig molecule itself, such as the absence of sialic acid moieties [39]. Furthermore, specific factors may be required within the IgG and/or target antigen(s) of the cryoglobulin, especially in the mixed cryoglobulinemias, since many cryoprecipitates form best between the cryoglobulin in association with the respective patient's IgG and/or its Fc, but not with IgG from normal serum [40]. These findings suggest that cryoglobulins result from the specific selection of antibodies with such characteristics by the pathologic processes responsible for cryoglobulin development, rather than emerging from a random, stochastic process.

Classically, the overproduction of cryoglobulins and the resulting aggregates and/or circulating immune complexes are thought to overwhelm normal mononuclear phagocyte system activity, perhaps by impairing normal Fc receptor function, leading to the accumulation of serum cryoglobulin complexes that deposit in target tissues where they induce disease [41,42]. Indeed, some familial forms of cryoglobulinemia have been associated with deficiencies in complement proteins [43,44] and presumably result from the inability of these patients to effectively clear cryoglobulin-containing immune complexes.

OVERVIEW OF CLINICAL PRESENTATION AND DISEASE ASSOCIATIONS — Clinical presentations of cryoglobulin syndromes vary substantially among series, probably due in large part to both differences of case definition and prevalence of secondary etiologies [3]. The majority of people with cryoglobulins are asymptomatic. When a clinically significant disorder is associated with the presence of cryoglobulins, the symptoms and physical findings are generally correlated with the underlying Brouet type of cryoglobulin. (See 'Classification' above.)

Type I cryoglobulinemia — Type I cryoglobulinemia classically produces symptoms and signs related to vascular occlusion by the cryoprecipitate such as digital ischemia, livedo reticularis, and skin necrosis [45-48]. Such manifestations are frequently dependent on a low outside temperature. Skin manifestations are most commonly observed in these patients, with reports of up to 70 to 85 percent. Raynaud phenomenon is also frequent, and in severe cases, without treatment of the underlying disease, may progress to digital gangrene. Estimates for the frequency of extracutaneous disease includes peripheral neuropathy in approximately 20 to 45 percent of patients, arthralgia in 30 percent, and renal disease in 30 percent. When the cryocrit is high, symptoms of hyperviscosity may occur that include blurring or loss of vision, headache, vertigo, nystagmus, dizziness, sudden deafness, diplopia, ataxia, confusion, dementia, disturbances of consciousness, stroke, or coma.

A nationwide retrospective study in France identified 64 patients with symptomatic type I cryoglobulins over a 15-year period [45]. All patients had either a hematologic malignancy (56 percent, most often Waldenström macroglobulinemia or multiple myeloma) or a monoclonal gammopathy of undetermined significance (MGUS; 44 percent). Cutaneous involvement, sometimes severe and resulting in ulcerations and necrosis, was often present; other common findings included peripheral neuropathy, as well as arthralgia or arthritis. Renal disease (usually a membranoproliferative glomerulonephritis) was seen in 30 percent of the affected patients. None of the patients exhibited central nervous system, pulmonary, cardiac, or gastrointestinal manifestations. Treatment for these symptoms included glucocorticoids, plasma exchange, alkylating agents, rituximab, and other chemotherapy; 10 percent of the patients did not require treatment. Ten-year survival was 87 percent, with relatively poorer survival rates in the patients with hematologic malignancy. Another report of a series of patients with symptomatic type I cryoglobulinemia showed that IgG cryoglobulins were mainly associated with MGUS and multiple myeloma, whereas IgM cryoglobulins were associated with MGUS and Waldenström macroglobulinemia [46]. These different cryoglobulin isotypes should have an impact on the choice of treatment as the target cell will be the B lymphocyte or the plasmocyte, respectively. The prognosis of type I cryoglobulinemia has largely reflected the usual underlying lymphoproliferative disorder, such as Waldenström macroglobulinemia or multiple myeloma. (See "Epidemiology, pathogenesis, clinical manifestations, and diagnosis of Waldenström macroglobulinemia", section on 'Hyperviscosity syndrome' and "Multiple myeloma: Clinical features, laboratory manifestations, and diagnosis".)

Mixed cryoglobulinemia (types II/III) — Mixed cryoglobulinemia is most often associated with constitutional and nonspecific symptoms, such as arthralgias, fatigue, and myalgias, as well as palpable purpura due to cutaneous vasculitis and sensory changes or weakness due to peripheral neuropathy [49]. The classical "Meltzer's triad" of purpura, arthralgias, and weakness is seen in most patients [9,50]. Purpura is the most common manifestation, usually involving the legs, but it can extend to the torso and upper extremities [47]. A membranoproliferative glomerulonephritis is seen in 20 to 30 percent of the affected patients. Manifestations often wax and wane over time, with spontaneous remissions and exacerbations [51]. Symptoms often last one to two weeks, recurring one to two times per month, but, in severe cases, discrete exacerbations may be difficult to discern.

SPECIFIC CLINICAL FEATURES

Cutaneous involvement and vasomotor symptoms — Cutaneous manifestations develop in nearly all patients with cryoglobulin syndromes [2,9,52-54] and may precede extracutaneous manifestations by decades. Typically, these lesions consist of erythematous macules and purpuric papules of the lower extremities (90 to 95 percent) (picture 2), though infarction, hemorrhagic crusts, and ulcers also occur (10 to 25 percent), generally in patients with type I cryoglobulinemia. Similarly, Raynaud phenomenon, livedo reticularis, and acrocyanosis more commonly manifest in type I cryoglobulinemia as mentioned above (see 'Mixed cryoglobulinemia (types II/III)' above). Postinflammatory hyperpigmentation (30 to 50 percent) and exacerbation as a result of cold exposure (10 to 30 percent) are common. Morphologic abnormalities of the nailfold vasculature, including tortuosity and apical enlargement, are seen on capillaroscopy [55].

Musculoskeletal involvement — Musculoskeletal complaints such as arthralgias and myalgias are common in the mixed cryoglobulinemias, but frank arthritis or myositis is rare [16,56]. Arthralgias are typically described in over 70 percent of patients, especially affecting the metacarpophalangeal and proximal phalangeal joints, knees, and ankles, often in type III cryoglobulinemia. They rarely accompany type I cryoglobulinemia.

Peripheral nerve involvement — Neuropathy affects a high percentage of patients with mixed, in contrast to type I, cryoglobulinemia. Electromyographic and nerve conduction studies have demonstrated the presence of peripheral neuropathy in over 70 to 80 percent of patients with mixed cryoglobulins [15,57-59], but many symptom-based demographic studies report prevalences of only 30 to 45 percent. Severe peripheral neuropathy, such as mononeuropathy multiplex or combined sensorimotor disease, is uncommon [60-62]. (See "Clinical manifestations and diagnosis of vasculitic neuropathies".)

Renal involvement — Renal disease in mixed cryoglobulinemia often results from immune complex disease or, less often, as a result of thrombotic disease (the latter is more often seen in type I disease) [2,63]. Cryoglobulinemia was the cause of biopsy-proven glomerulonephritis in approximately 2 percent of cases in an Italian registry of renal biopsies [64].

Membranoproliferative glomerulonephritis is more common in mixed cryoglobulinemia, and variations in underlying etiology likely account for the wide variation in the reported incidence of renal disease among various case series (5 to 60 percent). Isolated proteinuria or hematuria occurs much more frequently than nephrotic or nephritic syndromes or acute renal failure [65,66]. Most patients declare chronic or rapidly progressive disease course within three to five years of diagnosis. (See "Mixed cryoglobulinemia syndrome: Clinical manifestations and diagnosis".)

Pulmonary involvement — Subclinical pulmonary manifestations appear to be common in mixed, but not type I, cryoglobulinemia [67-69]. Pulmonary function tests often reveal evidence of small airways disease and impairment of gas exchange, with symptoms in approximately 10 to 20 percent of patients, usually ranging from dyspnea to cough and pleurisy. Organizing pneumonia, alveolar hemorrhage, and pulmonary vasculitis have been reported but appear to be very uncommon.

Other organ involvement — Other manifestations have been reported with varying frequency, such as lymphadenopathy in up to 20 percent; splenomegaly in up to 30 percent; and abdominal pain in up to 20 percent (which sometimes reflects active mesenteric vasculitis) [15,70]. Other manifestations such as hepatomegaly, abnormal liver function tests, or abnormal liver biopsy in up to 90 percent are not related to the cryoglobulinemia itself but to the main cause (eg, hepatitis C virus [HCV] infection). Clinically significant vasculitis of most other internal organs, such as of the heart, central nervous system, and retinal vessels, rarely complicates any of the cryoglobulinemia syndromes, with the possible exception of those with hyperviscosity due to type I cryoglobulinemia. However, pathologic findings suggest that more widespread, though subclinical, involvement may be more frequent. (See 'Biopsy' below.)

DIAGNOSTIC APPROACH

When to suspect the diagnosis — The range of clinical presentations associated with the various cryoglobulinemia syndromes is broad, but some of the more common features include arthralgia, purpura, skin ulcers, glomerulonephritis, and peripheral neuropathy. The index of suspicion for cryoglobulinemia should be raised further if these occur in the setting of a clonal hematologic disease (eg, multiple myeloma, Waldenström macroglobulinemia), viral infection (eg, hepatitis C virus [HCV], hepatitis B virus [HBV]), or connective tissue disease (eg, systemic lupus erythematosus [SLE], Sjögren's syndrome, or rheumatoid arthritis).

Overall, the presence of a measurable amount of cryoglobulin (cryocrit) with a low C4 complement level remain the most prominent laboratory hallmarks of cryoglobulinemia syndromes [52]. Several other serologic findings have often been reported, but none are pathognomonic since they are often encountered in healthy individuals and/or other confounding medical conditions.

Evaluation — The initial evaluation for patients with suspected cryoglobulinemic vasculitis should include an assessment for associated diseases as well as other possible comorbidities.

History and physical examination — Some of the key elements of the history include the following:

●Prior or concomitant history of a clonal hematologic disease (eg, multiple myeloma, Waldenström macroglobulinemia, monoclonal gammopathy of undetermined significance [MGUS])

●Concomitant autoimmune diseases such as SLE or Sjögren's syndrome

●Concomitant infection with HBV, HCV, or HIV

●Past or current skin purpura of the lower limbs

●Skin ulcers or thromboses when exposed to cold outside temperature

●Acute foot or wrist drop suggestive of a motor neuropathy from an ischemic process

●Constitutional symptoms and nonspecific symptoms such as fever, fatigue, weight loss, arthralgias, and myalgias

A careful physical examination helps identify potential sites of vasculitis and determine the extent of vascular lesions, the distribution of affected organs, and the presence of additional disease processes. Certain findings, such as diminished sensation to touch and motor weakness of the extremities due to neuropathic changes consistent with mononeuritis multiplex and palpable purpura, are highly suggestive of an underlying vasculitic process. A skin exam may reveal purpura, livedo reticularis, skin necrosis, or ulcers.

Laboratory evaluation — In addition to detection of cryoglobulins, laboratory testing for all patients with suspected cryoglobulinemia should include additional testing to assess the degree of organ involvement as well as determine the presence of associated diseases.

Detection of cryoglobulins — To detect cryoglobulin, 10 to 20 mL of blood are drawn into syringes and/or collection tubes that have been prewarmed to 37ºC without anticoagulants. These precautions are required because failure to prewarm may lead to false-negative results, due to loss of the cryoglobulin in the clotted blood (eg, if there is cooling below 37°C during collection, clotting, or centrifugation) and because the presence of anticoagulants may produce false-positive results due to the formation of cryofibrinogen or heparin-precipitable complexes.

After clotting at 37°C for one-half to one hour, the serum is separated by centrifugation at 37°C, placed in a graduated (Wintrobe) tube, and refrigerated (4°C) to allow the precipitation of cryoglobulin. In type I cryoglobulinemia, precipitates are often seen within 24 hours (sometimes in less than 90 minutes). However, three to five days are usually allowed for complete precipitation, especially for the mixed cryoglobulins, and some type II and type III cryoglobulins require up to seven days for precipitation (picture 1) [71]. Most laboratories will determine a cryocrit, which is a measure of the packed (centrifuged) volume of the precipitate as a percentage of the original serum volume at 4°C.

Further confidence that the precipitate is a true cryoglobulin is obtained by washing the precipitate three to six times in cold saline solution to reduce the possibility of precipitated salts or other proteins. In addition, the precipitate can then be redissolved in saline at 37°C to confirm the warm solubility of the cryoglobulins. At this time, cryoglobulin protein concentration can be determined by spectrophotometry. Further characterization can be accomplished by immunofixation, enzyme-linked immunosorbent assay (ELISA), or another specific immunologic assay.

Some laboratories perform further testing consisting of a measurement of absolute cryoglobulin concentration, along with a description of the components of the immune complexes, including mono- or polyclonality of IgM, IgG, IgA, IgE, kappa, and/or lambda light chains. In type II cryoglobulinemia, the monoclonal component is typically IgM kappa with rheumatoid factor (RF) activity.

The cryocrit in individuals without cryoglobulinemia is close to zero; generally, a cryocrit over 0.5 to 1 percent or cryoglobulin concentration over 50 mcg/mL is considered clinically significant [52,72,73]. The cryocrit in affected patients may approach 50 percent or may encompass the entire serum volume in type I cryoglobulinemia under conditions in which the monoclonal protein forms a gel.

The cryocrit is generally between 2 and 7 percent in type II and between 1 and 3 percent in type III disease, but there is a poor correlation between the cryocrit and clinical symptoms and features [74].

When cryoglobulinemia is suspected clinically, a negative result from routine laboratory testing for cryoglobulins does not exclude cryoglobulin-mediated disease [75]. The clinician may need to draw a new specimen after consulting with the laboratory staff or clinical pathologist to assure that procedures are in place for the appropriate handling of the patient's blood when the sample is obtained and transported and to be certain that the laboratory has the necessary equipment (particularly a temperature-controlled centrifuge) to prevent premature cooling of the sample.

Immunochemical analysis — After the detection of cryoglobulinemia, it is categorized by immunochemical analysis into three different types. In order to analyze the nature of the cryoglobulin, it must be redissolved by warming and subjected to laboratory testing to determine its Ig and complement components [4]. This is accomplished by performing immunofixation of the redissolved cryoglobulin by antibodies directed to various Ig heavy chains (IgG, IgM, etc) and light chains (eg, kappa and lambda) and to complement components (eg, C1q, C4, and C3) or similar immunologic analyses. (See "Laboratory methods for analyzing monoclonal proteins".)

Additional laboratory testing — Laboratory testing for all patients with suspected cryoglobulinemia should include the following:

●Serum chemistries and a urinalysis – A serum creatinine and urinalysis may help identify the presence of kidney involvement and the degree of injury if present.

●Complement – Diminished serum complement components may reflect ongoing consumption by cryoglobulin-containing or cryoglobulin-propagated immune complexes [9,76]. Type I cryoglobulins typically produce few serologic complement abnormalities. Mixed cryoglobulinemia sera often demonstrate reduced levels of total hemolytic complement (CH50) and early complement proteins C1q, C2, and C4, particularly in type II cryoglobulinemia. Rarely, monoclonal immunoglobulin may also cause C3 glomerulopathy or atypical hemolytic uremic syndrome by interfering with the regulation of the alternative pathway of complement. Of note, in mixed cryoglobulinemia, low levels of C4 are a major marker of disease activity. Levels of C3 are generally unaffected or only mildly diminished [77].

●Rheumatoid factor – RF is usually present, often at high levels, in sera of patients with type II mixed cryoglobulinemia.

●Viral serologies – Serologic studies, particularly for viral hepatitis, are always indicated during the laboratory evaluation of a patient with mixed cryoglobulinemia. Hepatitis C has been reported in 60 to 90 percent of patients with mixed cryoglobulinemia syndromes, but other populations may have lower rates [29,78]. Serologic studies for other agents, including hepatitis B, HIV, and Epstein-Barr virus, have been somewhat inconsistent but are generally worth at least considering during the workup of cryoglobulinemia [79,80].

●Acute phase reactants – Other tests appear to reflect a chronic inflammatory response. Acute phase reactants such as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are generally elevated, and the ESR can be strikingly so in type I cryoglobulinemia, reflective of the underlying monoclonal Ig. Mild to moderate hypergammaglobulinemia of IgM, IgA, and/or IgG also typifies mixed cryoglobulinemia, with extremely elevated levels more indicative of type I cryoglobulinemia.

●Other autoantibodies – Other autoantibodies that should be included as part of the initial evaluation for a patient with suspected cryoglobulinemia include an antinuclear antibody (ANA) test, as well as testing for other specific antibodies such as double-stranded deoxyribonucleic acid (dsDNA), anti-Sm, Ro/SSA, La/SSB, and U1 ribonucleoprotein (RNP) [3,9]. False-positive test results for antibodies to citrullinated peptide antigens (ACPA) in a small proportion of patients with hepatitis C-related cryoglobulinemia (7 percent) have been ascribed to nonspecific binding of Ig in the assay [81]. Antineutrophil cytoplasmic antibody (ANCA) should be included as part of the workup to distinguish cryoglobulinemic vasculitis from the possible ANCA-associated vasculitides. (See "Biologic markers in the diagnosis and assessment of rheumatoid arthritis".)

Specific testing in selected patients

Biopsy — Although often not required for diagnostic purposes, biopsies of affected organs can help provide histopathologic evidence of cryoglobulinemic vasculitis. Type I cryoglobulinemia (monoclonal Ig-containing) predominantly affects the skin, kidney, and bone marrow; the main pathologic features are related to thromboses. Mixed cryoglobulinemia syndromes (types II and III) predominantly involve the skin, kidney, and peripheral nervous system; the main features are related to immune complex vasculitis. The histopathologic findings on biopsies of affected organs are described below.

●Skin – Skin lesions in mixed cryoglobulinemia most often reveal leukocytoclastic vasculitis (50 percent), less commonly inflammatory or noninflammatory purpura (10 to 20 percent) (picture 3), noninflammatory hyaline thrombosis (10 percent), or postinflammatory sequelae (10 percent). Direct immunofluorescence microscopy of acute lesions often reveals deposits of IgM, IgG, and/or C3 complement.

By contrast, type I cryoglobulins more often induce noninflammatory thrombotic lesions, sometimes with evidence of cutaneous infarction or hemorrhage [2,52,82].

●Peripheral nerve – Peripheral nerve lesions typically demonstrate vasculitis, generally of the epineurial vessels, in mixed cryoglobulinemia [60,83-87]. Necrotizing vasculitis or demyelination may be present, with occasional deposits of Ig and/or complement [88]. Pauci-inflammatory occlusive lesions are sometimes seen as well, suggesting a primary role for neuronal ischemia in disease pathogenesis, and are more suggestive of type I cryoglobulinemia. Affected nerves often display axonal degeneration, likely secondary to disease of the vasa vasorum. Most studies have focused upon histopathology of sural nerve biopsies, which are presumed to reflect systemic neuronal damage.

●Kidney – On light and immunofluorescence microscopy, membranoproliferative pattern of injury of glomerulonephritis is most commonly observed (in 60 to 80 percent), with endocapillary proliferation and subendothelial and/or intraluminal deposits of cryoglobulins, Igs, and/or complement proteins (picture 4 and picture 5) [65,89]. Less commonly seen, but not mutually exclusive, are mesangial proliferative glomerulonephropathy, intraglomerular hyaline thrombi, and vasculitis with fibrinoid necrosis (approximately 20, 25, and 30 percent, respectively) [15,90,91].

Type I cryoglobulinemia generally produces noninflammatory glomerulopathies, including thrombotic and hypocellular lesions, without evidence of vasculitis. However, type I cryoglobulins may rarely produce frank glomerulonephritis, as was documented in two cases of membranoproliferative disease, both involving IgG monoclonal cryoglobulins of the same isotype [92].

When renal biopsy specimens are examined with electron microscopy, amorphous or granular dense subendothelial deposits may be present (picture 6). The presence of electron-dense deposits that have a "fingerprint"-like appearance (picture 7) may provide a clue to the presence of cryoglobulins [93].

●Bone marrow – In type I cryoglobulinemia, bone marrow examination often reveals evidence of an underlying hematologic condition, such as plasma cell malignancy in multiple myeloma. Few studies have systematically explored bone marrow findings in mixed cryoglobulinemia, but monomorphic clusters of small lymphocytes, often with plasmacytoid features and associated with overexpression of the B-cell lymphoma 2 proto-oncogene, have been described [94,95].

Electromyography — Electromyography (EMG) may be useful if symptoms of neuromuscular disease are present, such as findings of multiple mononeuropathy (also called mononeuritis multiplex). (See "Overview of electromyography".)

Imaging — Imaging studies should be guided by the clinical presentation. An example of such a study would include a computed tomography (CT) scan of the chest, abdomen, and pelvis when searching for a lymphoproliferative disorder.

Diagnosis — Diagnosis of a clinical disorder in association with cryoglobulinemia requires a careful consideration of combined clinical, laboratory, and pathologic data. Few investigators have adhered to any of the several proposed classification criteria for the cryoglobulinemia syndrome [96,97]. While there are no established diagnostic criteria, we generally diagnose cryoglobulinemia as follows:

●Demonstration of an elevated cryocrit, such as greater than 1 percent or greater than 50 mcg/L.

Plus one or more of the following:

●Clinical indicators of cryoglobulinemic vasculitis or thrombosis with skin, joint, renal, peripheral nerve, central neurologic, gastrointestinal, pulmonary, and/or cardiac involvement and diminished serum C4 concentration (notably in mixed cryoglobulinemia syndromes). Histologic confirmation of leukocytoclastic vasculitis on skin biopsy is not needed if the patient has typical palpable purpura.

●Direct histologic and immunochemical evidence of cryoglobulins from pathologic thrombotic or vasculitic specimens. While this direct demonstration of cryoglobulins may provide the most definitive evidence, it is rarely sought or performed in clinical practice or included in formal criteria. For example, tissue biopsies and histologic confirmation of the presence of cryoglobulins is not part of the classification criteria for cryoglobulinemic vasculitis proposed by the Italian Study Group on Cryoglobulinemia [96].

Occasionally, the clinician is faced with the diagnostic challenge of a patient with nonspecific symptoms, such as weakness or arthralgias in the presence of serum cryoglobulin. In such cases, evidence of a low C4 serum level or a frequently associated disorder, such as HCV infection or a clinically evident systemic disease (eg, Sjögren's syndrome) increases the likelihood of the presence of a clinically significant cryoglobulinemia syndrome.

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of cryoglobulinemia is broad and varies depending upon the clinical presentation, which can include signs and symptoms of cryoglobulinemic vasculitis or a hyperviscosity syndrome.

The differential diagnosis of cryoglobulinemic vasculitis includes other vasculitides that affect small- or medium-sized vessels; these include drug-induced small vessel vasculitis (hypersensitivity vasculitis), IgA vasculitis (IgAV; Henoch-Schönlein purpura), antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (eg, granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis [Churg-Strauss syndrome]), and infection-related vasculitis (eg, bacterial endocarditis, poststreptococcal vasculitis, and glomerulonephritis). Vasculitis associated with a connective tissue disorder (eg, systemic lupus erythematosus [SLE], rheumatoid arthritis, Sjögren's syndrome) may or may not be mediated by cryoglobulins. In addition, disorders that mimic the symptoms and findings of vasculitis, including infectious (eg, rickettsial infections, malaria, babesiosis), thrombotic, and embolic disorders (eg, antiphospholipid syndrome, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, atrial myxoma), may warrant consideration. Patients with chronic hepatitis C virus (HCV) infection may have membranoproliferative nephritis and arthralgias even in the absence of cryoglobulinemia, and these complications of HCV may overlap with findings of cryoglobulinemic vasculitis. The differential diagnosis of vasculitis is discussed in more detail elsewhere. (See "Overview of and approach to the vasculitides in adults", section on 'Differential diagnosis'.)

Slow flow and impaired tissue perfusion affecting many organs may be due to marked elevation of the cellular contents of the blood (eg, leukostasis, polycythemia), partial obstruction by sickled red blood cells, parasitized cells (eg, malaria, babesiosis), or increased viscosity due to polyclonal or monoclonal Igs that are not cryoglobulins (eg, Waldenström macroglobulinemia).

TREATMENT — The treatment of cryoglobulinemia depends upon the underlying disorder and upon the severity and nature of involvement.

In patients with symptomatic mixed cryoglobulinemia, the treatment is directed at the underlying infectious or autoimmune disorder, as well as the vasculitis that may occur. Treatment of mixed cryoglobulinemia is discussed in detail elsewhere. (See "Mixed cryoglobulinemia syndrome: Treatment and prognosis" and "Treatment and prognosis of Waldenström macroglobulinemia" and "Overview of the management of chronic hepatitis C virus infection" and "Hepatitis B virus: Overview of management".)

In patients with monoclonal (type I) cryoglobulin associated with a lymphoproliferative disorder, the treatment is focused on the underlying malignancy and the risk or presence of complications such as hyperviscosity syndrome. Some patients with hyperviscosity may require treatment with plasma exchange or other interventions. (See "Treatment and prognosis of Waldenström macroglobulinemia", section on 'Emergency management of hyperviscosity' and "Therapeutic apheresis (plasma exchange or cytapheresis): Indications and technology", section on 'Common uses of therapeutic apheresis' and "Multiple myeloma: Overview of management", section on 'Other complications'.)

PROGNOSIS — Prognosis generally relates to the underlying disease state(s) or developing complication(s), particularly in type I cryoglobulinemia, where the patient often suffers from a primary lymphoproliferative disorder [48]. Patients with type II cryoglobulinemia are at increased risk to develop a B-cell non-Hodgkin lymphoma. Several studies have suggested that a handful of findings suggests poorer outcomes (ie, age, gastrointestinal or pulmonary involvement, renal insufficiency, four or more extrarenal manifestations, hypertension, and infectious complications [2,52,98]), but little is known about the relative contributions of each. The presence of cryoglobulins per se does not seem to confer a significant morbidity or mortality risk over and above the underlying conditions.

Survival — Mean survival is approximately 70 percent at 10 years after the onset of symptoms and 50 percent at 10 years after diagnosis, with death typically resulting from infection and cardiovascular disease. The prognosis for such patients depends upon their response to treatment (see "Mixed cryoglobulinemia syndrome: Treatment and prognosis"). Some complications of cryoglobulinemia predict poorer outcomes, including renal failure and development of a lymphoproliferative or plasma cell disorder.

Hepatitis C virus (HCV)-associated cryoglobulinemic vasculitis is a severe disease with an estimated five-year mortality rate of 25 percent [1,99]. Apart from liver fibrosis, the prognosis of HCV-associated cryoglobulinemic vasculitis is mainly dependent on vasculitic involvement of the kidney, central nervous system, heart, and gastrointestinal tract. However, more recent series report much lower mortality rates by using all oral interferon-free antiviral combinations with greater efficacy and better tolerance, and less use of immunosuppressants. (See "Overview of the management of chronic hepatitis C virus infection", section on 'Antiviral therapy'.)

Renal failure — The risk of development of renal failure may be greater in those with hepatitis C-associated disease than in those with idiopathic (essential) mixed cryoglobulinemia. This was illustrated in one study of 17 patients, 11 of whom had hepatitis C infection; 5 of 11 of these patients developed renal failure, while none of the six patients free of infection had progressive renal disease [89]. (See "Overview of kidney disease associated with hepatitis C virus infection".)

Lymphoproliferative disorders — Secondary lymphoproliferative disorders sometimes occur, generally manifesting in type II patients 5 to 10 years after diagnosis, but do so in less than 5 to 10 percent of patients [100-102]. The malignancy is often a B-cell non-Hodgkin lymphoma, approximately 50 percent intermediate-to-high-grade lymphoma and approximately 50 percent low-grade tumors such as immunocytoma (70 to 80 percent), mucosa-associated lymphoid tumors, or centrocytic follicular lymphoma.

Among patients with hepatitis C-associated type II cryoglobulinemia, the incidence of non-Hodgkin lymphoma is estimated to be 35-fold higher than in the general population. The distribution of aggressive and nonaggressive histologic types is similar to that noted above for unselected patients with cryoglobulinemia. (See "Extrahepatic manifestations of hepatitis C virus infection", section on 'Lymphoma'.)

SUMMARY AND RECOMMENDATIONS

●Terminology – Cryoglobulins are immunoglobulins (Igs) in the serum that precipitate at temperatures below 37°C and redissolve on rewarming. Cryoglobulinemia refers to the presence of cryoglobulin in a patient's serum. This term is often used interchangeably with cryoglobulinemic vasculitis (or cryoglobulinemia syndrome). Cryoglobulinemic vasculitis (or cryoglobulinemia syndrome) refers to a systemic inflammatory syndrome that generally involves small-to-medium vessel vasculitis due to cryoglobulin-containing immune complexes. (See 'Terminology' above.)

●Classification – The Brouet classification criteria is the most commonly used system that classifies cryoglobulinemia into three different subgroups based on their Ig composition. These classification criteria are also useful in that the subgroups partly correlate with pathogenicity and clinical manifestations. (See 'Classification' above.)

•Type I – In type I cryoglobulinemia, the cryoglobulins are monoclonal Ig, typically IgG or IgM, and less commonly IgA or free Ig light chains. Type I cryoglobulinemia develops in the setting of protein-secreting monoclonal gammopathies such as a monoclonal gammopathy of undetermined significance (MGUS) or a B-cell lineage malignancy (eg, multiple myeloma, Waldenström macroglobulinemia, or chronic lymphocytic leukemia). (See 'Type I' above.)

•Type II – In type II cryoglobulinemia, the cryoglobulins are composed of a mixture of a monoclonal IgM (or IgG or IgA) with rheumatoid factor (RF) activity and polyclonal Ig. Type II cryoglobulins are often associated with persistent viral infections, particularly hepatitis C virus (HCV) infection, and are associated with the mixed cryoglobulinemia syndrome. Other clinical associations with type II cryoglobulinemia include autoimmune diseases (mainly systemic lupus erythematosus [SLE] and Sjögren's syndrome), lymphoproliferative disorders, and other infections such as hepatitis B virus (HBV) and HIV. (See 'Type II' above.)

•Type III – In type III cryoglobulinemia, the cryoglobulins are composed of a mixture of polyclonal IgG (all isotypes) and polyclonal IgM. These cases are often secondary to autoimmune disorders, but can also be associated with infections (mainly HCV). (See 'Type III' above.)

●Overview of clinical presentation and disease associations

•Type I cryoglobulinemia – Type I cryoglobulinemia classically produces symptoms and signs related to vascular occlusion by the cryoprecipitate such as digital ischemia, livedo reticularis, skin necrosis, and purpura. Raynaud phenomenon and skin manifestations are commonly observed in these patients and are closely dependent on cold outside temperatures. When the cryocrit is high, symptoms of hyperviscosity may occur. (See 'Mixed cryoglobulinemia (types II/III)' above and 'Specific clinical features' above and 'Overview of clinical presentation and disease associations' above.)

•Mixed cryoglobulinemia (types II/III) – Mixed cryoglobulinemia (types II/III) is most often associated with constitutional and nonspecific symptoms, such as arthralgias, fatigue, and myalgias, as well as palpable purpura due to cutaneous vasculitis and sensory changes or weakness due to peripheral neuropathy. Manifestations are not dependent on cold outside temperatures. The classical "Meltzer's triad" of purpura, arthralgias, and weakness is seen in most patients. (See 'Mixed cryoglobulinemia (types II/III)' above and 'Specific clinical features' above and 'Overview of clinical presentation and disease associations' above.)

●When to suspect the diagnosis – The diagnosis of a cryoglobulinemia syndrome should be suspected in patients presenting with arthralgia, purpura, skin ulcers, glomerulonephritis, and peripheral neuropathy. The index of suspicion for cryoglobulinemia should be raised further if these occur in the setting of a clonal hematologic disease (eg, multiple myeloma, Waldenström macroglobulinemia, MGUS), viral infection (eg, HCV, HBV, HIV), or connective tissue disease (eg, SLE, Sjögren's syndrome) (see 'When to suspect the diagnosis' above). Diagnosis of a clinical disorder in association with cryoglobulin requires a careful consideration of combined clinical, laboratory, and pathologic data. The presence of a measurable amount of cryoglobulin (cryocrit) with a low C4 complement level remain the most prominent laboratory hallmarks of cryoglobulinemia syndromes. (See 'Diagnosis' above.)

●Evaluation – The diagnostic evaluation for a case of possible cryoglobulinemic vasculitis should include a detailed history including infectious disease exposure (eg, hepatitis B or C virus, HIV), a prior history of a clonal hematologic disease (eg, multiple myeloma, Waldenström macroglobulinemia, MGUS) or systemic autoimmune disease (especially SLE or Sjögren's syndrome), and symptoms or manifestations that may characterize or exclude a suspected diagnosis; a careful physical examination; laboratory testing to include detection of cryoglobulins, serum chemistries, urinalysis, complement (especially C4 level), RF, viral serologies (particularly for HBV, HCV, and HIV), acute phase reactants, as well as other autoantibodies such as antinuclear antibodies (ANAs) and antineutrophil cytoplasmic antibody (ANCA). (See 'Evaluation' above.)

●Treatment – The treatment of cryoglobulinemia depends upon the underlying disorder and upon the severity and nature of involvement. In patients with mixed cryoglobulinemia (type II or III), the treatment is directed at the underlying infectious or autoimmune disorder, as well as the vasculitis that may occur. In patients with monoclonal (type I) cryoglobulin associated with a lymphoproliferative disorder, the treatment is focused on the underlying malignancy and the risk or presence of complications such as hyperviscosity syndrome. Some patients with hyperviscosity may require treatment with plasma exchange or other interventions. (See "Mixed cryoglobulinemia syndrome: Treatment and prognosis" and "Treatment and prognosis of Waldenström macroglobulinemia", section on 'Emergency management of hyperviscosity' and "Therapeutic apheresis (plasma exchange or cytapheresis): Indications and technology", section on 'Common uses of therapeutic apheresis' and "Multiple myeloma: Overview of management", section on 'Other complications'.)

●Prognosis – Prognosis generally relates to the underlying disease state(s) or developing complication(s), particularly in type I cryoglobulinemia, where the patient often suffers from a primary lymphoproliferative disorder. (See 'Prognosis' above.)

ACKNOWLEDGMENTS — The UpToDate editorial staff acknowledges Stanford L Peng, MD, PhD, and Peter H Schur, MD, who contributed to an earlier version of this topic review.