Axonal excitability and motor propagation velocity of peripheral nerves in patients with acute vascular lesions of the brain

The physiological functional loss of single thenar motor units in the stroke patients: when does it occur? Does it progress?

OBJECTIVE

We examined the time at which loss of functioning motor units occurs on the hemiparetic side, the relationship between that loss and hemiparetic severity, and how long that loss continues.

METHODS

Sample surface motor unit action potentials (S-MUAPs) were evoked in F-waves. They entirely represent the activity of the relative numbers of different shape S-MUAPs for each abductor pollicis brevis muscle. S-MUAPs from selected population of F-waves were averaged after aligning onset latency. Motor unit number was obtained by dividing the maximum M-potential negative peak amplitude by the averaged S-MUAP one.

RESULTS

The motor unit number on the hemiparetic side was significantly lower than that on the unaffected side in stroke patients who had suffered hemiparesis for more than 9 days. This motor unit loss was greater in patients with severe hemiparesis. One year after onset, the chronic stroke patients showed the same motor unit loss on hemiparetic side as they had 3-4 months after onset.

CONCLUSIONS

Motor unit loss on the hemiparetic side is present as early as the second week after onset and is correlated with hemiparesis severity, and this loss continues out to 1 year. This may be due to trans-synaptic degeneration that occurs secondarily to upper motor neuron lesion.

Physiologic decrease of single thenar motor units in the F-response in stroke patients

OBJECTIVE

To investigate the left-right difference and the reproducibility by the F-wave motor unit number estimation and to compare the motor unit number between the hemiplegic and unaffected side in stroke patients.

SETTING

A referral center and institutional practice providing outpatient care.

SUBJECTS

Seven healthy volunteers and 15 consecutive stroke patients.

DESIGN

Diagnostic statistical test and correlational study.

METHOD

Submaximal stimuli were used to evoke a sample of surface motor unit action potentials (S-MUAPs) in the F-waves that are entirely representative of the relative numbers of detected S-MUAPs of different sizes. The average S-MUAP amplitude was calculated from a selected population of F-wave responses for each abductor pollicis brevis (APB) muscle. The motor unit number was calculated by dividing the maximum M-potential negative peak amplitude by the average S-MUAP negative peak amplitude.

RESULT

There was no statistical difference between motor unit numbers on either side and between test and retest in this motor unit number estimation method among normal subjects. The motor unit number on the hemiplegic side was significantly lower than on the unaffected side (p < .05, Mann-Whitney test) among stroke patients.

CONCLUSION

The motor unit could decrease in the hemiplegic side after a moderate-to-severe hemiplegic stroke and this decrement might be due to the transsynaptic degeneration secondary to an upper motor neuron lesion.

Amplitude desynchronisation of evoked compound muscle action potentials in normal and uraemic subjects

Compound muscle action potentials of the extensor digitorum brevis were obtained in two groups of normal and uraemic subjects by stimulating the deep peroneal nerve at the ankle and at the capitulum fibulae. Particular attention was drawn to the index of desynchronisation supplied by the amplitude change in the muscle potential evoked by distal and proximal stimulation of the same nerve. Statistical studied confirmed the soundness of this index in the normal and in the pathological condition, and showed a significant increase of the values found in uraemic patients. The complex of the data pointed out the advantage of integrating the usual motor conduction velocity determination with the mentioned desynchronisation index.

Vincristine polyneuropathy in man. A clinical and electrophysiological study

A clinical and electrophysiological follow up study of 14 cases of hemopathic patients patients undergoing VCR therapy showed evidence that the drug has a direct action on the motor and sensory axon but not on the propagation velocity. Sensory nerves seem to be affected earlier and more than motor ones. Correlation was good between clinical and electrophysiological findings for both functions. The findings in man correspond with the animal data and therefore lead to the conclusion that VCR polyneuropathy is due to an involvement of the nerve axon.