Granuloma annulare (GA) is a common, benign inflammatory disorder classically characterized by asymptomatic, flesh-colored to pink or violaceous, nonscaly, annular plaques.
PATHOGENESIS AND EPIDEMIOLOGY
The pathogenesis remains unknown, although a delayed-type hypersensitivity to an unknown antigen has been hypothesized. Viral infections, autoimmune disease, trauma, and exposure to ultraviolet radiation have all been reported as inciting factors. Although GA may occur at any age, school-aged children are most commonly affected.
Common locations for GA include the lateral or dorsal hands, feet, wrists, and ankles (Fig. 354-1). Due to their annular (ie, ring-like) appearance, lesions are often misdiagnosed as tinea corporis (Fig. 354-2). However, unlike tinea infections, the lesions of GA have a smooth, sometimes firm border, without scale. This is because the histopathology of GA predominates in the dermis or sometimes the subcutaneous tissues, sparing the epidermis. The 4 main clinical variants include localized (which occurs in 75% of cases), generalized, perforating, and subcutaneous GA. Lesions of subcutaneous GA appear as asymptomatic to slightly tender, flesh-colored nodules that can occur anywhere, although they are often on the anterior lower legs and scalp. Atypical locations, including the palmar surfaces and eyelids, have been reported (Fig. 354-3). Adults who develop generalized GA may be more likely to have diabetes, but this association has not been established in children.
Dorsal hand with granuloma annulare. Note the annular pink plaque with smooth raised borders and no scale.
Annular pink plaque mimicking tinea corporis.
Firm, tender erythematous papule on ventral surface of finger.
The clinical differential diagnosis of GA includes tinea corporis, NL, rheumatoid nodules, cutaneous sarcoidosis, and mycobacterial infections including leprosy.
Skin biopsy is usually diagnostic in uncertain clinical cases. Histologically, GA displays altered collagen and mucin surrounded by distinctive “palisading” histiocytes. There are also interstitial variants where the collagen alteration is less obvious. In subcutaneous GA, the inflammatory process primarily involves the fat. Rarely, the malignant tumor epithelioid sarcoma, which can present as a slow-growing nodule on the upper extremity, may mimic GA on low-power histology. In such cases, immunohistochemical staining for cytokeratins, vimentin, and epithelial membrane antigen will support the diagnosis of sarcoma and rule out benign GA.
Evidence for treatment is limited to case reports and small case series. Topical steroids or intralesional steroids have been used to limit progression and may be modestly helpful. Systemic steroids, isotretinoin, hydroxychloroquine, dapsone, ...