Interstitial granulomatous dermatitis with plaques

We report on the clinical and histopathologic findings of four patients who had asymptomatic, erythematous to violaceous plaques symmetrically distributed on the upper aspect of the thighs, lateral chest, and in two cases also on the abdomen and flexor surface of the elbows. All of the patients were women; two of them had arthritis, which in one case was associated with an autoimmune disorder, and another had autoimmune thyroiditis. Histopathologically, all cases showed similar changes consisting of an interstitial granulomatous dermatitis involving mostly the lower reticular dermis. Histiocytes were the predominant cellular component, arranged interstitially and in small palisades around foci of degenerated collagen bundles in concert with large numbers of neutrophils and eosinophils. Interstitial granulomatous dermatitis can present different clinical expressions, including linear cords, papules, and, as in our cases, plaques. This peculiar histopathologic pattern falls into the spectrum of cutaneous extravascular necrotizing granuloma, a condition that is often associated with systemic autoimmune disease.