Diagnosis: Granuloma annulare
The diagnosis was granuloma annulare (GA), a common, benign skin condition with asymptomatic skin-colored to violaceous papules that typically coalesce to form arciform or annular plaques. Solitary umbilicated papules and nodules may also be seen, especially on the fingers. Most GA patients are younger than 30 years; the female-to-male ratio is approximately 2:1. While lesions of GA may occur anywhere on the body, they most commonly arise at acral sites; 60% of cases are localized to the hands and arms and 20% to the legs and feet.
A generalized form of the disease, which can occur in 15% of GA patients, is characterized by innumerable small skin-colored papules or annular plaques on the trunk and extremities. This type of GA has a later age of onset and poorer response to therapy. Other less common variants are deep dermal or subcutaneous GA, which presents as large painless, skin-colored, pseudorheumatoid nodules, and patch GA, which features erythematous patches on the trunk and extremities.
The etiology of GA is unknown. Histologically, GA is a granulomatous dermatitis characterized by interstitial lymphohistiocytic infiltrates, mucin deposition, and focal degeneration of collagen and elastic fibers. In 25% of cases, well-formed palisaded granulomas consist of a rim of histiocytes and lymphocytes surrounding a central zone of degenerated connective tissue and mucin.
The condition has been theorized to be a T helper cell (Th1) inflammatory reaction, like TB, i.e., lymphocytes that produce interferon-a orchestrate an inflammatory response that recruits histiocytes to the dermis, where the subsequent release of lysosomal enzymes results in damage to the surrounding connective tissue. The exact cause of this response is not known. Most cases of GA have no identifiable cause, although trauma, insect-bite reactions, tuberculin skin testing, and viral infections are some of the various inciting factors that have been implicated.
An association between GA and diabetes mellitus has been proposed though not confirmed; a number of reports and retrospective studies exist to support or refute the association. GA has also been reported as a rare paraneoplastic, granulomatous reaction to solid-organ tumors, Hodgkin’s disease, non-Hodgkin’s lymphoma, and granulomatous mycosis fungoides.
The duration of untreated lesions ranges from a few weeks to several decades, but on average, spontaneous resolution is seen in 50% of cases within two years. The recurrence rate of GA is approximately 40%; lesions often recur at the original site. Recurrent lesions tend to resolve more rapidly than primary lesions (80% within two years).
Given the self-limited and benign nature of the condition, treatment for a patient such as ours—with localized asymptomatic disease—generally consists of reassurance and observation. If therapy is desired, high-potency topical steroids (with or without occlusion) or intralesional steroid injections are considered first-line agents. Cryosurgery, psoralen-UVA phototherapy, and carbon dioxide laser treatment have also been used. A variety of systemic agents, including niacinamide, isotretinoin (Accutane), antimalarials, cyclosporin A, chlorambucil (Leukeran), dapsone, and pentoxyfylline (Trental), have been reported anecdotally as effective, but these are generally reserved for severe, refractory, and generalized cases.