Motor evoked potentials in motor neuron disease: parameters of evaluation and its relation to disease severity

ABSTRACT

Transcranial magnetic stimulation [TMS] is a technique that can activate cortical motor areas and the corticospinal tract without causing discomfort to the patients. To evaluate the parameters of MEP induced by TMS in MND and its relation to the severity of the disease. Twenty five subjects with motor neuron disease [MND] who had been diagnosed as MND using the standard clinical and electrophysiological studies [nerve conduction studies, EMG and the somatosensory evoked potential studies] had been subjected to TMS and the MEP parameters [threshold, central motor conduction time [CMCT], amplitude percentage quotient, phases and duration of the MEPs] were determined. Matched healthy persons were selected as control. Functional evaluation and disease severity assessment had been scored using the ALS Functional Rating Scale [ALSFRS] and the ALS Severity Score [ALSSS] respectively and compared to the control group. A statistical significant difference of all the motor evoked potentials [MEP] parameters of the studied patients and the scale measurements were present when compared with the control group. The mean central conduction time [CMCT] was correlated with the severity of the disease while the amplitude changes were evident in late stages especially when associated with bulbar manifestations whereas there was no correlation between MEP parameters and the functional rating scale. From these findings it would be recommended to use the TMS as a useful tool to determine the extent of the disease as well as to predict severity of motor neuron disease [MND]