Movement-related cortical potentials in primary lateral sclerosis

OBJECTIVE: Some patients with primary lateral sclerosis (PLS) have a clinical course suggestive of a length-dependent dying-back of corticospinal axons. We measured movement-related cortical potentials (MRCPs) in these patients to determine whether cortical functions that are generated through short, intracortical connections were preserved when functions conducted by longer corticospinal projections were impaired. METHODS: An electroencephalogram was recorded from scalp electrodes of 10 PLS patients and 7 age-matched healthy control subjects as they made individual finger-tap movements on a keypad. MRCPs were derived from back-averaging the electroencephalogram to the movement. RESULTS: MRCPs produced by finger taps were markedly reduced in PLS patients, including components generated by premotor areas of the cortex as well as the primary motor cortex. In contrast, the beta-band event-related desynchronization from the motor cortex was preserved. INTERPRETATION: These findings suggest that impairment in PLS is not limited to the distal axons of corticospinal neurons, but also affects neurons within the primary motor cortex and premotor cortical areas. The loss of the MRCP may serve as a useful marker of upper motor neuron dysfunction. Preservation of event-related desynchronization suggests that the cells of origin differ from the large pyramidal cells that generate the MRCP.