MEP recruitment curves in multiple sclerosis and hereditary spastic paraplegia.

OBJECTIVE

Axons remodel at multiple levels after a single inflammatory lesion in the spinal cord, which can contribute to recovery. The primary aim of this study was to investigate whether the MEP response as function of the excitatory strength, here called recruitment curves, may be used in discriminating demyelination from compensated axonal loss. Multiple sclerosis (MS) represents both demyelination and axonal degeneration. Hereditary Spastic Paraplegia (HSP) was included as a model of pure axonal loss.

METHODS

To investigate both spinal and cortical recruitment, the methods used for gradual recruitment were two different test paradigms of voluntary pre-activation and stimulus intensity. The MEP-recruitment curves were obtained by means of transcranial magnetic stimulation (TMS) in 29 MS patients, 9 patients with HSP and in 30 healthy controls.

RESULTS

Saturated recruitment curves were obtained in all subject groups, muscles and paradigms and were generally found to be identical. The two groups of patients had clinical signs, CMCT changes and reduced MEP amplitude reflecting relevant cortico-spinal disorder.

CONCLUSIONS

We conclude that both demyelination and axonal degeneration in the CNS leads to diminished MEP amplitudes and CMCT changes. The recruitment curves of MS and HSP was identical to controls and may not be used for diagnostic or monitoring purposes.