Focal myositis associated with S-1 radiculopathy: report of two cases.

Two cases are described of pseudotumoral calf hypertrophy after laminectomy for a compressive S-1 radiculopathy. The serum creatine kinase (CK) level was normal or mildly elevated. T2-weighted magnetic resonance imaging (MRI) showed calf enlargement, with an increased signal of the medial head of the gastrocnemius muscle. Electromyography revealed fibrillation potentials and positive sharp waves, but no complex repetitive discharges in the affected gastrocnemius muscle, with motor unit potentials having mixed neurogenic and myopathic features. Muscle biopsy revealed a focal myositis associated with some features of denervation. A brief course of corticosteroids was followed by remission clinically and improvement in the MRI findings.