The patient was diagnosed with granuloma annulare on the basis of history and clinical exam. A potassium hydroxide prep of skin scrapings was performed to rule out tinea corporis, and did not show evidence of fungal elements. The patient was treated with topical betamethasone with partial improvement.
First described as a “ringed eruption of the fingers” by Thomas Colcott Fox in 1895, granuloma annulare (GA) is a relatively common, benign, and self-limited condition whose precise etiology remains unclear. It is characterized commonly by pink to violaceous aciform or annular plaques on clinical examination. In some cases of GA, annular lesions are not present, or may be formed of grouped papules.
GA is characterized histologically by patchy interstitial lymphocytes and histiocytes palisading around mucin. Deep GA, an unusual subtype observed only in children, features a fibrin rather than a mucin core. This granulomatous picture is consistent with a Th1-mediated inflammatory process, and indeed, macrophage tumor necrosis factor production, as well as interleukin-2 and interferon-gamma production have been observed in GA. The reason for this exaggerated Th1 response is unknown, although in susceptible individuals trauma3 (an example of the Koebner phenomenon), arthropod assault,4 and herpes simplex infection5 (an example of Wolf isotopic response) all have been observed to trigger localized and/or generalized GA. Generalized GA has been associated with hyperlipidemia and the human leukocyte antigen–BW35 allele. GA has been described as a paraneoplastic eruption; atypical features such as associated pain or appearance in an uncharacteristic location often are present in such cases.6,7
Diagnosis of typical GA is clinical. If unusual features make you suspect tinea, leprosy, mycosis fungoides, or other annular lesions, then biopsy showing features typical of GA can reveal the correct diagnosis. Biopsy also can help to distinguish papular GA from warts or molluscum contagiosum. If extensive GA are present, then serum lipid testing for hypercholesterolemia or hypertriglyceridemia should be considered.
Other annular and raised lesions are on the differential for GA, but careful attention to the patient’s history and examination can clarify the diagnosis. Urticaria multiforme, a variant of annular urticaria, presents with numerous annular and polycyclic wheals, sometimes with central darkening that may be mistaken for necrosis. This patient did not present with polycyclic wheals. Furthermore, the lesions in urticaria multiforme are typically transient, with individual lesions lasting less than 24 hours, which was not the case with this patient. Wells syndrome, also known as eosinophilic cellulitis, is a condition marked by recurrent episodes of pruritus followed by appearance of edematous, painful, indurated, or edematous papules or plaques, although bullae and vesicles also may be present. The face and extremities are frequently involved and spontaneous resolution typically occurs in 2 months. Annular lesions are possible but papules, plaques, and nodules are more common in Wells syndrome. Annular elastolytic giant cell granuloma (AEGCG), also known as actinic granuloma and Miescher granuloma of the face, is an entity characterized clinically by chronic, persistent, sun-distributed, annular plaques typically seen in older women with significant sun damage. AEGCG is considered by some to be a variant of GA, but if this is the case, it is a distinct subtype with different epidemiologic, clinical, and histopathologic characteristics from GA. Interstitial granulomatous dermatitis is histologically and clinically distinct from GA, presenting as subtly erythematous cords or extensive annular or serpiginous plaques in the axilla, groin, buttocks, or chest, typically in adult patients with rheumatoid arthritis, reactive arthritis, psoriatic arthritis, or ankylosing spondylitis. Tinea corporis, the clinical manifestation of cutaneous dermatophyte infection, may be mistaken for granuloma annulare. However, tinea corporis lesions are scaly, whereas GA does not scale. Histologic examination of tinea corporis reveals hyphae, which are not present in GA.
GA is a relatively common, idiopathic, benign skin disease with numerous annular and papular mimics. Absence of scale, pain, and significant pruritus are important clues to the diagnosis, and biopsy can be helpful when the diagnosis is unclear. Treatment, although not necessary, may be offered using any of a number of modalities. The most consistent and effective healer of GA, however, is time.