INTRODUCTION — Nummular headache is one of several relatively uncommon headache syndromes that may occur either as a primary headache or as a headache symptomatic of potentially malignant processes. Careful evaluation for underlying causes is important for these uncommon types of headache.
This topic will review nummular headache. Other types of uncommon primary headache disorders are discussed separately. (See "Primary stabbing headache" and "Primary cough headache" and "Exercise (exertional) headache" and "Primary headache associated with sexual activity" and "Overview of thunderclap headache" and "Hypnic headache".)
PATHOPHYSIOLOGY — Nummular headache may be neuralgia of a terminal branch of the trigeminal nerve [1], although its pathophysiology is uncertain. In one series of 23 patients with nummular headache, there was a high prevalence of serum markers of autoimmunity and autoimmune disorders [2], suggesting a possible relationship between autoimmunity and nummular headache.
CLINICAL FEATURES — Also called coin-shaped headache, nummular headache is characterized by small circumscribed areas of continuous pain on the head [3-5]. Nummular headaches are generally of mild to moderate intensity and confined to a round or elliptical unchanging area 2 to 6 cm in diameter. The pain is continuous or intermittent, although in a large minority of cases, spontaneous remissions lasting weeks to months may occur. Superimposed on the continuous pain, lancinating pain may occur that initially lasts seconds but may gradually increase in duration to minutes or hours [3,6,7]. The affected area may be allodynic, paresthetic, or hyperesthetic [5]. The parietal region is the area of scalp most often affected [4].
While nummular headache is typically unifocal, a few patients have been reported with focal head pain in two separate areas [7,8]. One series of 16 patients with nummular headache found a disproportionately high occurrence of comorbid migraine (56 percent) [9].
Nummular headache is not accompanied by nausea, vomiting, light or sound sensitivity, rhinorrhea, lacrimation, conjunctival injection, or focal neurologic symptoms.
Nummular headache is uncommon, with an estimated incidence of 6.4 per 100,000 [6].
DIFFERENTIAL DIAGNOSIS — The differential diagnosis includes primary (idiopathic) stabbing headache, which unlike nummular headache, tends to be multifocal and variable in location. (See "Primary stabbing headache".)
The differential also includes headache resulting from cranial bone lesions caused by metastatic cancer, multiple myeloma, Paget disease of bone, hemangiomas, osteomyelitis, or other cystic lesions [3,10]. In one case, a patient had symptoms typical of primary nummular headache that localized to the left posterior parietal region, where a protruding lesion about 1 cm long was identified on head MRI but not on CT [11]. The lesion ended in a point with the bone layer preserved, but its precise nature was unknown. Nummular headache has also been associated intracranial lesions including two cases with fusiform aneurysms of a superficial scalp vessel and one case of a cavernous malformation [10,12].
Although there is no clear consensus among experts, we suggest obtaining a head CT or MRI to evaluate for both neoplastic and infectious bone lesions in patients with suspected nummular headache. MRI may have a higher sensitivity than CT in this setting, but data are limited.
TREATMENT — Treatment with gabapentin (900 to 1800 mg daily) has been reported to be transiently effective and may be attempted [1,13]. A prospective, nonrandomized study evaluated 53 patients with nummular headache and found that treatment with onabotulinumtoxinA injections was associated with improvement; the mean a number of headache days per month decreased from 24.5 at baseline to 6.9 between weeks 20 and 24, and the 50 percent responder rate was 77 percent [14]. There is also a case report of successful treatment with indomethacin (25 mg twice daily) [15]. However, nummular headache often becomes refractory to all standard prophylactic and analgesic therapies [16].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Neuropathic pain" and "Society guideline links: Migraine and other primary headache disorders".)
SUMMARY AND RECOMMENDATIONS
●Clinical features – Also called coin-shaped headache, nummular headache is characterized by small circumscribed areas of continuous pain on the head, sometimes accompanied by superimposed lancinating pain. Spontaneous remissions lasting weeks to months may occur. (See 'Clinical features' above.)
●Imaging evaluation – For patients with suspected nummular headache, we suggest obtaining a head CT to evaluate for metastatic and infectious cranial bone lesions. (See 'Differential diagnosis' above.)
●Treatment – Treatment with gabapentin (900 to 1800 mg daily) or botulinum toxin injections may be transiently effective, but nummular headache often becomes refractory to all standard headache therapies. (See 'Treatment' above.)
