Papular sarcoidosis of the knees: a clue for the diagnosis of erythema nodosum-associated sarcoidosis

BACKGROUND: In recent years we have systematically explored the skin whenever sarcoidosis was suggested and we have observed with increasing frequency the presence of granulomatous cutaneous lesions of sarcoidosis involving the knees. OBJECTIVE: We sought to evaluate the specific cutaneous lesions of sarcoidosis involving the knees. METHODS: A total of 18 patients with biopsy-proven specific cutaneous sarcoidosis predominantly involving the knees were included in the study. Biopsy specimens were evaluated under polarized light. RESULTS: Of these cases, 4 corresponded to scar-sarcoidosis, 1 to plaque-type sarcoidosis, and 13 were an admixture of papules and minute scars frequently associated with erythema nodosum (papular sarcoidosis of the knees). Foreign particles were observed in 10 of 13 patients with papular sarcoidosis. CONCLUSION: Papular sarcoidosis of the knees can be considered a frequent form of cutaneous sarcoidosis, mainly observed in acute forms of the disease, and frequently associated with erythema nodosum.