Adipophilin expression in necrobiosis lipoidica, granuloma annulare, and sarcoidosis.

Necrobiosis lipoidica (NL), granuloma annulare (GA), and sarcoidosis usually are distinguished by clinical presentation and routine microscopy, but their distinction can sometimes be challenging. Historically, a clue to diagnosing NL or GA has been the identification of lipid droplets in the areas of altered collagen, but such studies have required fresh frozen tissue, making them impractical. Here, we present the first report of immunohistochemical staining to detect adipophilin, a membrane protein in lipid droplets, in NL (n = 12), GA (n = 19), sarcoidosis (n = 12), and, as a control for nonspecific tissue damage, nongranulomatous cutaneous necrosis (n = 13). Four patterns of labeling were identified: (1) extracellular, within zones of altered collagen; (2) both intracellular and extracellular, after the distribution of palisaded or scattered histiocytes; (3) intracellular, within clustered histiocytes; and (4) periadnexal. All cases of NL demonstrated pattern 1; nearly all cases of GA (18/19) demonstrated pattern 2; most sarcoidosis (10/12) demonstrated pattern 3; and nongranulomatous necrosis demonstrated either pattern 4 (6/13) or did not stain (6/13), confirming that the antibody to adipophilin did not adhere nonspecifically to the damaged tissue. An additional set of 3 biopsies with overlapping or partially sampled features of NL, GA, and/or sarcoidosis subsequently confirmed the potential utility of adipophilin staining in diagnostically challenging cases. We conclude that the pattern of adipophilin expression is a useful adjunct in the evaluation of granulomatous dermatitis.