Granuloma annulare (GA) is a benign, typically selflimited, cutaneous disorder that is classically described as papules coalescing into annular plaques. There is a female predominance of 2.5:1, and the majority of patients are first affected prior to age 30. Localized GA is the most common clinical presentation, though clinical variations include generalized, subcutaneous, patch, and perforating forms. The most well-accepted hypothesis regarding pathogenesis involves a delayed-type hypersensitivity reaction. Other postulated mechanisms include vasculitis, trauma, and lysosomal enzyme release from monocytes induced by sensitized lymphocytes. Reported triggers include tuberculin skin tests, insect bites, sun exposure, and viral infections. GA has occurred in siblings and twins, and generalized GA has been associated with HLA Bw35, suggesting a genetic link. Lymphoma, solid organ malignancy, and leukemia have been reported in older patients with atypical GA lesions, but no definitive correlation exists. Similarly, the relationship between GA and diabetes mellitus has been debated for decades, and data remain inconclusive. A recent case-controlled study revealed a higher prevalence of dyslipidemia in GA patients, especially those with generalized GA.

The lesions of GA are asymptomatic or mildly pruritic and most commonly present on the extremities, occasionally on the trunk, and rarely on the face. The subtypes differ in morphology, distribution, and age of those affected. While lesions may remit, reoccurrence is not uncommon (Table 17-1).

Localized GA is the most common subtype and presents as flesh-colored, arciform, or annular plaques on the extremities in limited quantity (Fig. 17-1). Plaque diameter ranges, and some lesions can measure upward of 5 cm. The age of onset is usually prior to 30, but localized GA can occur in older individuals. Approximately half of cases self-resolve; however, resolution can take years and recurrence at the same anatomic sites is common.

Generalized GA occurs in approximately 15% of GA patients, presents in a disseminated fashion on the trunk and extremities, and typically excludes mucous membranes, face, palms, and soles (Fig. 17-2). The lesions vary in color (skin-toned, red, tan, or yellow) and morphology (patches and papules) and can present as individual lesions or form reticulate or circinate patterns. Unlike the localized form, the age of onset for generalized GA is bimodal— either younger than 10 years or older than 40 years, and spontaneous resolution is less likely.

Perforating GA, subcutaneous GA, and patch GA are more rare (Figs. 17-3 and 17-4). Perforating GA affects both children and young adults and presents on dorsal hands and fingers. Lesions are primarily papules with a pustular-like,
umbilicated, or crusted component that may eventually develop into scars. Subcutaneous GA exists as deep-seated nodules or superficial papules on the hands, palms, feet, shins, and periocular region, more often in children than adults. Patch GA more commonly affects adults with red patches distributed on the trunk and extremities. Annular lesions may be seen.