G.P.33 - Clinical and pathological features in SMA patients, confirmed by genetic analysis

Abstract

Spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by degeneration of the anterior horn cells of the spinal cord, resulting in symmetrical limb muscle atrophy and weakness. It is difficult to diagnose SMA patients in some cases, because of its clinical presentations mimicking muscular dystrophies. We aimed to describe clinical and pathologic characteristics of SMA patients, confirmed by genetic test. We reviewed clinical and pathological features of 14 patients, who were completely done with electrodiagnostic study (EDX) and muscle biopsy, and diagnosed as SMA with genetic study from November 1, 2005 to December 31, 2013. Among 14 patients, 8 patients (57.1%) were male. The mean age of symptom onset was 35 months old. Mean age at final genetic diagnosis was 21.1 years old and mean duration between clinical and genetic diagnosis was 7.3 years. All patients showed proximal dominant weakness and their most common first symptoms were both leg weakness. With clinical, EDX and muscle biopsy findings, 10 patients (71.4%) were diagnosed as SMA, but other 4 patients (28.6%) were diagnosed as myopathy. Those 4 patients showed proximal dominant weakness and their first symptoms were both leg weakness, meaning their CK levels were 395 U/L, higher than clinical and pathologically SMA group (45 U/L). Among them (9 patients), EDX showed chronic neurogenic process of 3 patients and myopathic change in 1 patient. Muscle biopsy presented myopathic change with 3 patients, no pathologic diagnosis with 1 patient and neurogenic change in 1 patient. Even though the results of muscle biopsy and electrodiagnostic study show ‘myopathic change’, genetic study of SMN1 gene may show ‘exon 7, 8 deletions’. It is helpful to consider the genetic test for SMN1 gene when we diagnose patients with unspecified neuromuscular disease.