Motor neuron disease is generally regarded as different manifestations of the same disease. They show degeneration of the motor cells in the cord and brain stem with concomittant fasciculation, atrophy and paralysis. Degeneration of the corticospinal tracts may be the initial lesion in amyotroph colateral sclerosis, in which there are no sensory disturbances. The groups of progressive spinal muscular atrophies would included bulbar, palsy, amyotrophic lateral sclerosis, progressive spinal muscular atrophy, and peroneal muscular atrophy. Electromyography performed in muscles innervated by both the posterior and the anterior primary divisions of the spinal nerves may reveal abnormal findings. At rest there are potentials of denervation fibrillation and of fasciculation. These are found in greatest .a.undance in ,those muscles which show visible atrophy but can also be found to a lesser degree i i remote parts, reflecting - the-wide, spread character of involvement. The fasciculation potentials are usually polyphasic in shape and of long duration. Synchronization occurs with an incidence of 60 percent. In atrophies, caused by involvement of the anterior horn cells there is an increase in both a-meanduration and the amplitude of the action potentials. The more advanced the disease, the more pronounced is the increase of the action potentials. Normal motor units are also found in inverse relation to the severity of the lesion.
Some uninvolved muscles may exhibit electrical silence at rest and normal recruitment of motor unit activity during contraction. In the adult form of progressive spinal muscular atrophy pat ological, findings of denervation fibrillation. and fasciculation are found in greatest number in the small muscles of the hand. The rest of the arm, shoulder and trunk muscles reveal minimal findings except in the more advanced stage.
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