Sarcoid granulomas on scars.

Whereas visceral sarcoid granulomas are often clinically silent, skin lesions can provide useful clues to the clinician. Sarcoid granulomas can develop on old scars. Inflammation, infiltration and induration of the scar are the typical manifestations. Because these changes can occur at any time during the course of the disease, scars in patients with suspected or known sarcoidosis should be examined periodically. The pathogenesis of sarcoidosis remains obscure. In practice, changes in an old scar should lead to a biopsy aimed at detecting sarcoidosis. Because of the close similarities between sarcoid granulomas and silicotic granulomas, specimens should be examined carefully under a polarized light microscope. Demonstration of crystalline inclusions within the granuloma cells suggests silicosis but does not rule out sarcoidosis. Investigations for systemic involvement should be done. The presence of sarcoid granulomas at other sites establishes the diagnosis. In patients with negative investigations, only long-term follow-up can tell whether sarcoidosis is the cause of the scar lesions.