Granuloma annulare induced by scabies.

Abstract

Sir, Granuloma annulare (GA), a granulomatous disease of unknown aetiology, is characterized by small papules that are often fused into annular arrangements. Several variants are known: localized GA, generalized GA, subcutaneous GA, perforating GA and arcuate dermal erythema. Localized GA is the most common of the subtypes; 9 – 15% are afflicted with the generalized variant. The other subtypes are rare. Children and young adults are those predominantly affected – women twice as often as men. Human leucocyte antigen (HLA)-B8 has been reported to be increased in localized GA, while HLA-A31 and HLA-BW35 are reported to be increased in the generalized GA. Proposed pathogenic mechanisms of GA include cellmediated immunity (type IV), immune complex vasculitis and abnormalities of tissue monocytes, diabetes mellitus, thyroid disease, HIV and hepatitis C infection appear to be predisposing factors. Aside from these predisposing factors, trigger factors seem to play an important role in the development of the disease. GA may appear following other disease at the same site: mycobacterial and fungal infections, herpes simplex infection, herpes zoster, erythema multiforme minor and insect bites can lead to the manifestation of GA. An isomorphic phenomenon (Koebner reaction) is the assumed pathophysiologic mechanism for these observations. However, to the best of our knowledge a case of GA induced by scabies infection has not been described previously.