Pattern of denervation in clinically uninvolved limbs in patients with prior poliomyelitis

In most cases of poliomyelitis, motor neuron death is extensive. In mild cases primarily involving one limb, the pattern of neuron death has not been fully determined. Nine mildly affected patients were studied systematically for electrophysiologic evidence of denervation by sampling one muscle in each limb. Fiber density was found to be increased in all but one muscle. Needle electromyography and turns and amplitude plots of the interference pattern were abnormal in all muscles in weak limbs and the majority of muscles in unaffected limbs. Turns: amplitude ratios were lower in muscles in weak limbs and greater in muscles in unaffected limbs in a pattern suggesting a horizontal gradation of motor neuron death across the spinal cord. This may be attributed to axonal transport of the virus. The horizontal pattern of sub clinical involvement in mild cases of poliomyelitis was compared and found to be similar to reported patterns of progression of limb weakness in amyotrophic lateral sclerosis type motor neuron disease.