F wave measurements detecting changes in motor neuron excitability after ischaemic stroke.

OBJECTIVE

To study mechanisms that are involved in the hyperexcitability of spinal motor neurons in upper motor neuron lesion, by means of F-wave measurements.

METHODS

F waves from 44 hospitalized stroke patients and 35 healthy controls were recorded from abductor pollicis brevis muscles in the course of two experiments: (1) single stimuli following high-intensity ipsilateral cutaneous conditioning were used to stimulate the median nerve; (2) paired stimuli were given to the median nerve at gradually increasing interstimulus intervals to assess recovery curves. Mean F-wave amplitudes elicited by the conditioning stimuli were compared with mean F-wave amplitudes elicited by the test stimuli on both the hemiparetic and the unaffected side.

RESULTS

There was no reduction on the hemiparetic side of mean F-wave amplitudes elicited following high-intensity ipsilateral cutaneous stimulation. The recovery of mean F-wave amplitude was completed at longer interstimulus intervals on the hemiparetic side than on the unaffected side and in controls. A correlation was found between this delay of recovery and hemiparetic severity.

CONCLUSIONS

The results of our study support the role of changes in lower motor neuron membrane excitability in the enhancement of F wave amplitudes after stroke.