Localized muscle wasting as an initial symptom of skeletal muscle lymphoma.

A 25-year-old man who developed painless muscle wasting and weakness of only the right thigh, was eventually shown to have systemic lymphoma with muscle infiltration. The patient was initially misdiagnosed as focal inflammatory myopathy, and he had a partial response to steroid therapy. Immunohistochemical analysis of the biopsied muscle and the subcutaneous tumor revealed the infiltrating cells with a positive macrophage-associated marker (CD68) and negative T- or B-cell-associated antigens, leading to the final diagnosis of true histiocytic lymphoma. Although skeletal muscle lymphoma is extremely rare, it should be considered in the differential diagnosis of localized muscle wasting.