Central Motor Physiology in Polio Survivors

Many persons who survive poliomyelitis develop pain, weakness, and fatigue many decades later. It is not known why some persons develop this syndrome and others do not. One possibility is that polio caused subclinical damage to the motor cortex. Autopsies in some polio patients have found damage to the brainstem and motor cortex as well as to spinal motor neurons. Alternatively, polio may have spared the motor cortex, but the cortex reorganized in different ways to compensate for the loss of spinal motor neurons. This study will first assess the integrity of central motor pathways in polio survivors with and without postpolio syndrome. The second goal will be to investigate differences in the intracortical mechanisms for controlling muscles affected and unaffected by polio.

STUDY POPULATION: 60 patients who survived polio in childhood. Only patients with an unequivocal history of polio will be referred to this study. Half of the patients will have the post-polio syndrome. 30 normal volunteers, aged 21-80.

DESIGN: Patients will be screened at the collaborating institution, the Uniformed Services University of the Health Sciences, which will also perform sensory evoked potential testing. At NIH, motor evoked potentials will be elicited from all four limbs using transcranial magnetic stimulation to assess central motor conduction time and threshold. MRI scans of the brain or spine will be performed in patients with abnormal evoked potentials. Intracortical facilitation will be assessed using paired-pulse magnetic stimulation. Two muscles will be tested in each patient, one affected by polio and one unaffected by polio. In the affected muscle, intracortical facilitation will be assessed again after exercises it until it fatigues.

OUTCOME PARAMETERS: Cortical thresholds and central motor conduction times to all four limbs will be measured in patients and compared to normal subjects. The mean intracortical facilitation at rest will be compared in affected and unaffected muscles in polio patients with and without post-polio syndrome.