[A case of spinal muscular atrophy with marked calf hypertrophy and adolescent onset]

We report on a 41-year-old male patient with spinal muscular atrophy (SMA). He had slowly progressive muscular weakness and hypertrophic calves since 14 years of age. The upper arms were slightly, and the thighs moderately atrophic, but the calves were remarkably hypertrophic. There was muscle weakness of both the upper and lower limbs, being more proximal in distribution. He had a positive Gowers' sign and his gait was slightly waddling. Serum creatine kinase level was elevated (518IU/l). Electromyogram revealed a neurogenic pattern. Muscle biopsy of the left biceps brachii showed chronic neurogenic changes. Immunohistochemical examination and Western blot analysis using anti-dystrophin antibodies showed no abnormality. DNA analysis with multiplex PCR proved no deletion in the dystrophin gene, while deletions of exons 7 and 8 of the telomeric copy of survival motor neuron gene were detected. In 1978, Pearn et al. described a new variant syndrome of SMA, characterized by adolescent onset, gross hypertrophy of calves, and a slowly progressive clinical course. The present case is compatible with this syndrome. Therefore, it is suggested that this syndrome, mimicking Becker muscular dystrophy, is not an independent clinical entity, although the phenotype of this syndrome is different from that of typical SMA.