Name That Rash!

A healthy young adult presents with an asymptomatic lesion on their skin (below are various pictures of the same lesion in different patients, all on extremities). What is it? What causes it? Is it contagious? And how do we treat it?

Sources: Wikipedia, Primary Care Dermatology Society

Granuloma annulare (GA) classically presents as a localized papule that evolves into an annular plaque, which lacks peripheral scale.

The cause of GA is unknown, although multiple etiologies have been suggested (e.g., viral-induced, drug-induced, etc); regardless, it is not contagious.

Approximately 75% of patients with GA have a single localized lesion, as pictured above; 15% have generalized GA, which typically presents with numerous papules/plaques on the trunk and extremities. Localized GA is self-limited but slow to resolve (often 2-4 years); treatment with intralesional steroids or high-intensity topical steroids (e.g., topical clobetasol) may speed resolution.

GA may be confused with other conditions such as tinea corporis, pityriasis rosea, or nummular eczema. The lack of any surface changes to the skin is the key feature that distinguishes GA from these other conditions. Specifically, there is no scale or associated vesicles or pustules with GA; the skin surface is smooth. Other key differences:

  • Tinea lesions have scale and +KOH prep
  • Pityriasis rosea more often appears on the trunk, initially as a herald patch followed by multiple similar lesions
  • Nummular eczema lesions are very itchy and lack central clearing
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