A 54-Year-Old Man with Progressive Lower Limb Weakness and CK Elevation

Amyotrophic lateral sclerosis (ALS) caused by Cu/Zn superoxidase dismutase 1 (SOD1) gene mutations is a rare condition that accounts for about 20% of familial ALS (FALS) and up to 7% of sporadic ALS (SALS) cases. It is largely an autosomal dominant disease, which is characterized by progressive limb, bulbar, and respiratory muscle weakness from degeneration of upper and lower motor neurons. Although the SOD1 gene test is commercially available, the diagnosis of this disease is still quite challenging, requiring a high clinical suspicion and accurate interpretation of nerve conduction study and electromyogaphy, serum creatine kinase level, and muscle biopsy findings. Muscle biopsy typically shows prominent chronic active denervation with pseudomyopathic changes. Here we describe a patient with FALS caused by an SOD1 gene mutation. He had been misdiagnosed with lumbosacral polyradiculopathy and myopathy for 2 years.