Interstitial Granulomatous Dermatitis: A Clinicopathological Study.

INTRODUCTION: Interstitial granulomatous dermatitis (IGD) is an uncommon granulomatous dermatitis occurring in the setting of highly reactive immune states, with a polymorphic clinical presentation. Because there is overlap with other entities [namely palisading neutrophilic granulomatous dermatitis (PNGD)], controversy exists regarding its classification. OBJECTIVE: To understand if there are features allowing clear-cut distinction between IGD and PNGD. MATERIAL AND METHODS: Retrospective analysis of 10 cases previously diagnosed as IGD or PNGD, from 2000 to 2013, with review of the histopathologic findings and clinical correlation. RESULTS: Six females and 4 males presented mostly with erythematous papules/nodules (n = 7) but also with erythematous annular plaques (n = 3). In 2 patients, the lesions coexisted. They were mostly distributed symmetrically on the limbs. Associated disease was observed in 6 patients. Regarding histopathology, an inflammatory infiltrate occupying the superficial and mid dermis was present in 40% of cases, with an interstitial component in all biopsies and a palisaded arrangement in 60%. Neutrophils and mononuclear cells were present in all cases in varying proportions. Necrobiosis was found in 70%, and leukocytoclasia was observed in 80% of biopsies. CONCLUSIONS: Coexistence of the interstitial and palisaded inflammatory patterns occurred in 90% of cases, with no correlation between tissue neutrophilia and the predominant pattern of the infiltrate. There was also no clear-cut correlation between the infiltrate pattern and semiologic aspect of the lesions. Therefore, the features described in our study suggest that IGD and PNGD belong to the same clinicopathological spectrum.