Spontaneous resolution of focal eosinophilic myositis of the adductor pollicis complicated by lung lesions.

Eosinophilic myositis is characterised by peripheral blood eosinophilia and eosinophilic infiltration in muscles, and is comprised three subtypes: focal eosinophilic myositis (FEM), eosinophilic polymyositis, and eosinophilic perimyositis. Muscle involvement of FEM is usually limited to the lower legs, and pulmonary complications have not been reported. We report a rare case of FEM in the left adductor pollicis complicated by lung lesions. A 37-year-old woman developed swelling of the first web space in the left hand. Magnetic resonance imaging (MRI) of the left hand demonstrated increased signal on fat-suppressed T2-weighted imaging in the left adductor pollicis. A muscle biopsy specimen demonstrated perimysial and endomysial infiltration of mononuclear cells and eosinophils, and necrosis and regeneration of muscle fibres. Chest computed tomography (CT) revealed upper-lobe-dominant ground-glass opacities (GGO). Both focal myositis and pulmonary lesions improved without treatment. This case suggests that FEM could involve adductor pollicis and have pulmonary lesions. In this case, myositis and GGO resolved spontaneously. Some FEM cases treated with glucocorticoids were reported in the past. Further studies are required to determine whether patients with FEM require therapeutic intervention.