Reactive Granulomatous Dermatitis (Interstitial Granulomatous Dermatitis, Palisaded Neutrophilic and Granulomatous Dermatitis, and Variants)

Cutaneous granulomatous inflammation may arise in association with systemic diseases or medication exposure. These reactive processes have been the focus of a number of reports since first being described, with what has become a complex nomenclature with overlapping clinical and histologic descriptions. While distinctions have been proposed between “interstitial granulomatous dermatitis (IGD),” “palisaded neutrophilic and granulomatous dermatitis (PNGD),” “interstitial granulomatous drug reaction (IGDR),” and “drug-induced interstitial granulomatous dermatitis (D-IGD),” recent advances in understanding reactive granulomatous processes support efforts to reclassify these entities under a single umbrella term. In 2015, “reactive granulomatous dermatitis (RGD)” was proposed as an umbrella term highlighting the significant overlap of clinical and histologic features of PNGD, IGD, and IGDR and the commonly associated systemic associations. Rather than existing as distinct entities, PNGD, IGD, and IGDR can be thought of as variants or subtypes of RGD. In this chapter, we review RGD and variants with a focus on nomenclature, epidemiology, clinical features, and histology and review the suggested workup and treatment options.