erythema elevatum diutinum
a rare chronic symmetrical eruption of flattened nodules of a pinkish or purplish color, occurring in plaques on the buttocks; Achilles tendons; and extensors of wrists, elbows, and knees, becoming fibrotic and finally scarring. Early lesions show necrotizing vasculitis with fibrinoid or lipid deposits in vessel walls.
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Examples: glitazone, GI cocktail, etc.