INTRODUCTION — Tinea nigra is a superficial mycosis caused by the dematiaceous, yeast-like fungus Hortaea werneckii. The infection most often presents as an asymptomatic, hyperpigmented macule or patch on the palm (picture 1A-C). Less frequently, tinea nigra occurs on the soles of the feet or in other locations (picture 2A-C). The course of tinea nigra tends to be chronic; however, the infection resolves quickly with appropriate treatment.
The clinical features, diagnosis, and management of tinea nigra will be reviewed here. Other cutaneous fungal infections are reviewed separately.
●(See "Dermatophyte (tinea) infections".)
●(See "Tinea capitis".)
●(See "Tinea versicolor (pityriasis versicolor)".)
MICROBIOLOGY — Tinea nigra is classified as a superficial phaeohyphomycosis, a group of fungal infections caused by dematiaceous (pigmented) fungi. The main etiologic agent is H. werneckii, a fungus previously classified in the genera Phaeoannellomyces and Exophiala [1,2]. H. werneckii is a pleoanamorphic fungus that grows as a black yeast and can transform into a mold.
H. werneckii is halotolerant and halophilic (survives and thrives in high salt concentrations), osmotolerant, and grows in aqueous media. The fungus readily adapts to hypersaline conditions ranging from 3 to 30 percent sodium chloride [1-6]. H. werneckii has been isolated in various environments, including coastal areas (beaches and sand), mangrove plants (Aegiceras corniculatum), desalination plants, and desiccated puddles [3,7-9].
Other fungi reported to cause tinea nigra include Cladosporium castellanii (also known as Stenella araguata) [10,11], Phoma hibernica [12], and Cladophialophora saturnica (spp nova) [13].
EPIDEMIOLOGY AND RISK FACTORS — Tinea nigra is an uncommon condition for which epidemiologic data are limited. It is estimated that tinea nigra accounts for less than 1 percent of superficial fungal infections. Tinea nigra may occur at any age but most often occurs in children and young adults. There does not appear to be a sex predilection.
Tinea nigra is most common in individuals who visit or reside in tropical and subtropical climates [1]. Most reported infections have occurred in Central and South America (Mexico, Panama, Brazil, Colombia, and Venezuela), Asia (Japan, India, Sri Lanka, and Burma), Polynesia, and the coasts of Africa [2,14-18]. Tinea nigra is rarely diagnosed in Europe; reported infections are generally acquired outside of Europe [19,20]. In the United States, both native and non-native (returning traveler) cases have occurred. Florida, North Carolina, and South Carolina appear to be the most common states for native infections [21-23]. It is likely that most patients become infected in aqueous environments (eg, rivers, lakes, and marine areas).
Palmar or plantar hyperhidrosis is an important predisposing factor for tinea nigra. In one series, 9 of 22 patients (41 percent) with tinea nigra had hyperhidrosis [2]. The association is probably due to the high saline concentration of sweat, which produces similar conditions to the natural niche of the fungus [1,22]. (See 'Microbiology' above.)
PATHOGENESIS — Tinea nigra develops following direct contact with the fungus in the environment. Minor skin trauma can contribute to infection, which contributes to the palm as a common location. Plantar infections tend to occur in individuals who have walked barefoot in wet or sandy areas (eg, beaches). The incubation period is not well defined; in a series of 22 patients, the estimated time to the development of visible lesions was approximately two to four weeks from inoculation based upon patient recollection [2]. Infection is not thought to occur through human-to-human transmission.
On the skin, H. werneckii grows in the form of hyphae and brown spores. The depth of infection is limited to the cornified layer of the epidermis, which becomes hypertrophied as a result of infection. Rarely, tinea nigra may lead to H. werneckii infection in other sites; H. werneckii peritonitis has been reported in a peritoneal dialysis patient with tinea nigra on the palm [24].
CLINICAL FEATURES — The most common presentation is a unilateral, hyperpigmented, irregularly-shaped but well-circumscribed macule or patch with fine scale on the palm of the hand (picture 1A-C) [1,2,14,15,18,19,25]. The color typically ranges from light to dark brown. Erythema is usually absent. Bilateral involvement is rare and may result from autoinoculation [2,26].
Although approximately 80 percent of patients have involvement of the palm, tinea nigra occasionally occurs on the fingers or interdigital spaces (picture 2C) [2,17,18]. Infection on the dorsum of the hand is uncommon. The second most common location is the foot, particularly on the soles, and, infrequently, in the interdigital spaces (picture 2A-B) [27]. In a series of 22 patients, 3 patients (14 percent) had involvement of the sole of the foot, and the remainder had palmar involvement [2]. Less frequent locations include arms, legs, neck, and trunk [1,2,14,15,19,25,28].
Most patients are asymptomatic. Occasional patients report pruritus; in these patients, mild erythema may be seen at the site of infection.
Without treatment, the course of tinea nigra tends to be chronic. However, spontaneous resolution within two to three months has been reported [2,29].
DIAGNOSIS — A diagnosis of tinea nigra can be strongly suspected based upon the physical finding of a new-onset brown macule or patch, particularly when located on the palm and occurring in an individual who resides in or who has visited a tropical or subtropical location. Dermoscopic examination can aid in clinically distinguishing tinea nigra from melanocytic lesions. To confirm the diagnosis, a potassium hydroxide (KOH) preparation is typically performed. A culture can also confirm the diagnosis and will identify the causative organism.
Dermoscopy — Dermoscopy is helpful for differentiating tinea nigra from melanocytic lesions, such as acral nevi and melanoma. Typical dermoscopic findings are brown spicules that do not follow the ridges or furrows of the acral dermatoglyphics (skin lines) (picture 3) [1,2,30-36]. However, the occurrence of spicules following a parallel ridge pattern has been reported [37,38]. Additional findings obtained with super-high magnification dermoscopy include linear forms with undulated shape corresponding to brown, elongated hyphae and spindle-shaped blastoconidia [39]. (See "Dermoscopy of pigmented lesions of the palms and soles".)
Potassium hydroxide preparation — A KOH preparation can confirm fungal infection. Scrapings from affected skin are placed on a glass side with 10% KOH and examined with a microscope. In tinea nigra, microscopic examination reveals numerous light brown fungal elements formed by septate, variegate, and branched hyphae (picture 4) [1,2,14,15]. Clusters of blastoconidia or chlamydoconidia also may be seen. (See "Office-based dermatologic diagnostic procedures", section on 'Potassium hydroxide preparation'.)
Culture — A superficial scraping of affected skin (similar to the scraping performed for a KOH preparation) usually provides a sufficient specimen for culture. Cultures to identify H. werneckii are performed on Sabouraud dextrose agar and Sabouraud dextrose agar plus antibiotics media and incubated at 25 to 28°C. On average, fungal growth is evident within five to six days [2].
In the initial yeast-like phase, fungal colonies are smooth, slimy, and olive green to black; in the subsequent mold phase, the fungus manifests as filaments with a wooly or velvety appearance (picture 5). In the yeast-like phase, abundant budding cells with annellides and characteristic septae are visible with microscopic examination (picture 6). Microscopic examination of the mold phase exhibits thick, septate hyphae with conidiophores from which sprout numerous arborescent conidia in blastogenic or acropetal formations [1,2,15,19]. If desired, the cultured fungus can be definitively identified through polymerase chain reaction testing [2,40].
Biopsy — A skin biopsy is not typically necessary for diagnosis. Skin biopsies are generally performed if an alternative diagnosis (eg, melanoma) is suspected. Characteristic histologic findings of tinea nigra include (picture 7) [1,2,30,41]:
●Hyperkeratosis
●Mild acanthosis
●Numerous hyphae and pigmented spores within the stratum corneum
Inflammation is usually absent; occasionally, perivascular mononuclear cell infiltrates are present in the dermis.
Electron microscopy is not necessary for diagnosis but will demonstrate small colonies of fungi with hyphae and blastoconidia within the epidermis [42].
DIFFERENTIAL DIAGNOSIS — The differential diagnosis for tinea nigra includes other potential causes of skin (particularly acral skin) pigmentation, such as:
●Melanocytic nevi
●Lentigines
●Melanoma [43,44]
●Dermatitis neglecta (skin hyperpigmentation resulting from inadequate skin cleansing)
●Skin discoloration from metals contacting the skin (eg, metal rings)
●Palmar lichen planus (picture 8) [45]
●Phytophotodermatitis (eg, berloque dermatitis (picture 9))
●Fixed drug eruptions (picture 10)
A potassium hydroxide (KOH) preparation, fungal culture, or skin biopsy will distinguish tinea nigra from these disorders. (See "Lichen planus" and "Acquired hyperpigmentation disorders", section on 'Phytophotodermatitis' and "Fixed drug eruption".)
Atypical clinical and KOH preparation findings should raise the possibility of an alternative fungal infection. Superficial infections with other dematiaceous fungi, such as Exophiala mansoni [46], Neoscytalidium dimidiatum (previously Scytalidium) [47], or Aureobasidium melanogenum [48], may present with cutaneous hyperpigmentation and a positive KOH preparation. As an example, in a patient with A. melanogenum infection, hyperpigmented patches involved the face, were less well defined than typical tinea nigra, were accompanied by erythematous papules, and demonstrated dark, septate oval cells with thick septae and septate hyphae on a KOH preparation [48]. In such patients, fungal cultures are useful for definitive diagnosis [2].
TREATMENT — Topical therapy is the preferred mode of treatment for tinea nigra. No randomized trials have evaluated treatments for tinea nigra. Clinical experience and case reports support the efficacy of:
●Topical antifungal medications – Topical imidazoles such as bifonazole [2,49], clotrimazole [26], isoconazole [50,51], ketoconazole [52], miconazole [53], and sertaconazole [54], as well as terbinafine [50,55], butenafine [56], and ciclopirox [57]
●Topical keratolytics – 3% salicylic acid, Whitfield ointment (6% benzoic acid and 3% salicylic acid) [2]
In our experience, other topical agents, including 1% iodine tincture and 3% sulfur, can also be effective.
Tinea nigra generally responds rapidly to these therapies. A typical treatment course is twice daily application for two to three weeks. Clinical resolution should occur within this period. In our experience, concomitant treatment of hyperhidrosis (when present) can be necessary. (See "Primary focal hyperhidrosis", section on 'Palmar or plantar hyperhidrosis'.)
If tinea nigra fails to respond to topical treatment, the diagnosis and patient adherence to the treatment regimen should be confirmed.
Tinea nigra usually does not recur after treatment. However, continued contact with environmental conditions favorable for H. werneckii is a risk factor for reinfection.
Systemic therapy is not usually indicated and rarely necessary. In a case report, 200 mg of oral itraconazole per day for three weeks led to resolution of tinea nigra [58]. In our experience, 100 mg of itraconazole per day for 15 to 30 days can be sufficient for adults with recurrent tinea nigra. In an in vitro study that assessed susceptibility of H. werneckii to nine antifungal drugs, itraconazole was one of several drugs with a low minimum inhibitory concentration [59].
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Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Tinea nigra (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Tinea nigra is an uncommon cutaneous fungal infection that primarily results from infection with Hortaea werneckii, a dematiaceous (pigmented) fungus. H. werneckii grows in aqueous environments and can survive in high salt concentrations. (See 'Microbiology' above.)
●Tinea nigra typically occurs in individuals (most often children and young adults) who have visited or reside in tropical or subtropical climates. The infection occurs through direct contact with the fungus in the environment. It is likely that most patients become infected in aqueous environments, such as beaches of rivers, lakes, and marine areas. Hyperhidrosis is a risk factor for infection. (See 'Epidemiology and risk factors' above and 'Pathogenesis' above.)
●Tinea nigra usually presents as a unilateral, hyperpigmented, irregularly-shaped but well-circumscribed, brown macule or patch with fine scale. The palm of the hand is the most common site of involvement (picture 1A-C). Less often, tinea nigra occurs on the feet, on other sites on the hand, or in other body areas (picture 2A-C). The infection is usually asymptomatic. (See 'Clinical features' above.)
●The diagnosis of tinea nigra is made based upon consistent physical findings and confirmation of fungal infection. A potassium hydroxide preparation or fungal culture can be used to confirm fungal infection. (See 'Diagnosis' above.)
●Tinea nigra responds rapidly to appropriate therapy. We suggest treating with topical rather than systemic agents (Grade 2C). Topical antifungal mediations and topical keratolytics are common effective treatments. (See 'Treatment' above.)
