PROFILES OF NEUROMUSCULAR DISEASES - SPINAL MUSCULAR-ATROPHY

Forty-five individuals with spinal muscular atrophy (SMA) types II and III were evaluated prospectively over a 10-yr period to develop an im pairment and disability profile. SMA II subjects showed marked weaknes s and progressive decline of strength. Mean manual muscle test (MMT) s core for all muscles combined was 2.3 +/- 0.6, with a decline in stren gth of -0.24 MMT units per decade. SMA III individuals had a relativel y static or very slowly progressive course and were far stronger. Mean MMT score for all muscles combined was 3.8 +/- 0.7, and the decline i n strength per decade was not significant. In both types proximal weak ness was greater than distal, but there was greater involvement of the lower extremities and the extensor muscle groups only in SMA II. Cont ractures, progressive scoliosis, and restrictive lung disease (RLD) we re present in most of the SMA II individuals, but these complications were rare in SMA III. Maximal expiratory pressures were affected earli er and to a greater degree than vital capacity. Seventy-eight percent of those with SMA II had scoliosis with a mean Cobb angle of the prima ry curve of 62 +/- 37 degrees. Forty-one percent had severe RLD, and 1 7% had moderate RLD. In both types, 63% had abnormal electrocardiogram s although most had minor findings. Timed motor performance and functi onal evaluations indicated that muscle weakness translated to substant ial disability in both SMA II and III, with more severe impairment not ed in SMA II. Neither type was associated with abnormal mean scores on intellectual and neuropsychologic test batteries.