Interstitial granulomatous drug reaction with a histological pattern of interstitial granulomatous dermatitis

The interstitial granulomatous drug reaction (IGDR) is a novel drug-associa ted entity, characterized by violaceous plaques With a predilection for ski n fold areas. Light microscopically, it resembles the incipient diffuse int erstitial phase of granuloma annulare. Differentiating light microscopic fe atures include the absence of complete collagen necrobiosis, the presence o f interface dermatitis, and variable lymphoid atypia. The lack of vasculiti s rules out the extravascular necrotizing granuloma (Winkelmarm granuloma) associated with systemic disease. The differential diagnosis with interstit ial granulomatous dermatitis with arthritis as defined by Ackerman et al. h as not been studied until now. Our aim was to determine the histologic crit eria allowing us to differentiate IGDR without interface dermatitis and lym phoid atypia from interstitial granulomatous dermatitis. We report three pa tients with IGDR triggered, in two cases by respectively angiotensin conver tin enzyme (ACE) inhibitors and furosemide, and in one case by the associat ion of an ACE inhibitor; furosemide, and fluindione. Histologic examination showed a histological pattern of interstitial granulomatous dermatitis. We found a dense, diffuse histiocytic infiltrate distributed interstitially a nd in palisaded array within the reticular dermis. Eosinophils and some neu trophils were scattered throughout the infiltrate. In some tiny foci, envel oped by histiocytes, thick collagen bundles associated with basophilic nucl ear debris or "flame figures" were seen. Vasculitis, interface dermatitis, or lymphoid atypia were absent. Our study allowed us to expand the histolog ical spectrum of IGDR including a histological pattern similar to interstit ial granulomatous dermatitis. The lack of degenerated collagen could be a s ubtle clue in favor of interstitial granulomatous dermatitis triggered by a drug.