Diffuse plane xanthomatosis associated with a monoclonal band displaying anti-smooth muscle antibody activity

We report a patient with diffuse planar xanthomatous lesions associated with a benign monoclonal gammopathy. This patient has a very high titre of anti-smooth muscle antibody (1:10,240), but normal liver function tests and a normal liver biopsy. The paraprotein band displays anti-smooth muscle antibody activity. There is no evidence of any other underlying disease process. The findings are consistent with a diagnosis of diffuse plane xanthomatosis, but the mechanism of xanthoma formation remains unclear.