The histologic spectrum of cutaneous sarcoidosis: a study of twenty-eight cases.

Background: Naked sarcoidal granulomas (NSGs) are the characteristic histologic finding in sarcoidosis. This descriptive study was designed to identify the frequency of other histologic changes in cutaneous sarcoidosis.
Methods: The slides from 28 sequential biopsies previously diagnosed as sarcoidosis in patients with known systemic sarcoidosis were reviewed.
Results: Classic NSGs were identified in 25 biopsies (89%). Four biopsies contained tuberculoid granulomas, two with neutrophils suggesting infection (cultures negative). Five biopsies contained interstitial granulomas that resembled granuloma annulare and necrobiosis lipoidica in one case each. Additional histologic findings included birefringent foreign material in 14 biopsies (50%), focal necrosis (43%), elastophagocytosis (39%), linear peri-neural granulomas resembling leprosy (25%), increased dermal mucin (18%) and lichenoid inflammation (14%) [two with plasma cells resembling syphilis (7%)]. In all but three cases, the clinical morphology of the lesions suggested sarcoidosis. Special stains for mycobacteria and fungi were negative.
Conclusions: The histologic changes in cutaneous sarcoidosis are more diverse than previously recognized. In sarcoidosis, foreign material may be a frequent nidus for cutaneous granuloma formation. Histologic examination without the clinical history could lead to a misdiagnosis of leprosy, syphilis, other infectious granulomas, rosacea, granuloma annulare, necrobiosis lipoidica, and foreign body reaction in selected cases from this series.