Granulomatosus

Abstract

The disease entities in the group of granulomatous disorders share some histological commonalities, however the etiology of most remain largely unknown. In previous editions, the authors offered a schematic by which to classify granulomatous inflammation based on appearance, precipitating factors, and degree of lymphocytic infiltration ('non-immunologic vs. immunologic') but warned us that the distinctions are more apparent than real. More than a decade later, this caveat holds true. Granulomatosus represents a distinctive reactive process in the spectrum of inflammation where the histiocyte is the key involved cell. A granuloma is a focal collection of activated and modified histiocytes, sometimes 'epithelioid' in appearance, usually surrounded by a rim of leukocytes. While histiocytes are now firmly established as monocyte/macrophage-derived cells based on surface immunohistochemical markers, past reliance solely on cell morphology has led to confusion as numerous diverse, reactive, and neoplastic cell populations can aggregate in the cutaneous microenvironment resembling histiocytes, commonly referred as 'histiocytoid'.