Dermatomyositis, lobar panniculitis and inflammatory myopathy with abundant macrophages

Dermatomyositis (DM) is a rare treatable muscle disorder with a reported favorable outcome in most patients. A localized skin/muscle involvement in a DM patient raises questions of definition and causes such as lymphoma, or relapse. We describe here a young treated DM patient who presented a focal biopsy-proven destructive myositis and dermatitis restricted to the left thigh 15 months after the onset of a treated dermatomyositis. There was evidence of subcutaneous lobular panniculitis, somewhat resembling cytophagic histocytic panniculitis associated with a focal inflammatory myopathy with abundant macrophages that destroyed the sartorius muscle. Mild signs of hemophagocytosis and T-CD3 lymphocytosis were present in the bone marrow, but no monoclonal T-lymphocyte expansion was observed, as searched by autoradiography of the totality of TcR Vγ families. The patient improved with prednisone and azathioprine. We conclude that this focal complication suggests a continuum between dermatomyositis, CHP, and IMAM, the three syndromes where T-cell activation plays an important role.