Focal myositis (FM) is a rare disease characterized by focal inflammatory enlargement in a single skeletal muscle, and usually is cured without medication.1 It is important to distinguish FM from other diseases, especially localized nodular myositis, in which multiple nodular myositis could often develop into a generalized inflammatory disease, polymyositis.2
A healthy man, aged 43 years, experienced left femoral muscle pain and enlargement in November 1997. A muscle biopsy from his left quadriceps femoris revealed inflammatory myopathy. His symptoms gradually improved without medication. In January 2004, he recognized again the gradual left femoral swelling without other complaints. In April 2004, his left thigh became 5 cm thicker than his right one, with a mild pushing pain, and he was admitted to our hospital. He had no muscle weakness. The result of a blood test showed no particular abnormality, including serum creatine kinase level, erythrocyte sedimentation rate, and antinuclear antibody and anti-Jo1 antibody levels. T2-weighted magnetic resonance imaging revealed increased signal intensity within the left quadriceps femoris with gadolinium enhancement (Figure, A). The result of a second muscle biopsy from the left quadriceps femoris also showed infiltration of mononuclear cells and myopathic changes (Figure, B). Gallium citrate Ga 67 scintigraphy showed gallium uptake only in the left quadriceps femoris (Figure, C). The patient was diagnosed as having a relapse of FM, and his symptoms gradually improved without medication.