Granuloma Annulare-Like Lesions in a Patient With Sarcoidosis: Case Report and Review of Literature.

Sarcoidosis and granuloma annulare (GA) are two granulomatous skin conditions with significant clinical and histopathologic overlap, whose diagnosis may be further complicated by their potential to co-exist within a similar patient. Evolving literature supports the utility of special staining and immunohistochemistry (IHC) to aid in distinguishing these and other granulomatous skin disorders. Herein we report an interesting case of GA-like lesions in a patient with sarcoidosis, the elucidation of which was aided by immunohistochemical analysis. A 50-year-old man with an established history of sarcoidosis presented to the clinic with erythematous papules and plaques on his left elbow. Skin biopsy showed a granulomatous infiltrate consisting of histiocytes palisading around necrobiotic collagen with an accompanying perivascular lymphohistiocytic infiltrate. Staining with colloidal iron (increased mucin), CD123 (clusters of plasmacytoid dendritic cells), and adipophilin (highlighting histiocytes and necrobiosis), along with the histologic features supported a diagnosis of GA. The distinction between these two entities is important, as sarcoidosis may manifest systemically. Our case adds to the limited existing literature on GA-like lesions in sarcoidosis, underscoring the utility of special stains and IHC to help render the most accurate diagnosis for the patient.