Adult spinal muscular atrophy. A report of four cases

Four cases of spinal muscular atrophy (SMA) are reported, 3 with detailed autopsy findings. These are compared with 2 cases of typical amyotrophic lateral sclerosis (ALS) with neuropathological data. The 3 autopsy cases of SMA only showed decreased numbers of anterior horn cells in the spinal cord, with no change in the cortical pyramidal cells, including the Betz cells, and no degeneration of the pyramidal tracts, while the ALS cases showed loss both of lower and upper motor neurons and degeneration of the pyramidal tracts. In our opinion, the infantile, juvenile, adult, and late-life forms of SMA are really a single disease entity that occurs at varying ages and is separate from ALS. The term lower motor neuron disease would be preferable because the lesions are not limited to the spinal cord, but also occur in the brain stem.