Cortical magnetic stimulation in amyotrophic lateral sclerosis

Forty patients with ALS underwent cortical magnetic stimulation. Twelve had marked pseudobulbar signs; in these motor evoked potentials (MEPs) could not be elicited. Mean MEP latencies in the others, who had predominantnantly lower motor neuron signs, measured 23.3±2.1 msec (thenar), 18.7±5.3 msec (EDC), and 13.4±2.9 msec (biceps), respectively. These values were significantly longer (P > 0.001) compared with normal values (n=35), which measured 20.2±1.6, 14.2±1.7, and 9.4±1.7 msec, respectively. MEP amplitude was often markedly reduced (less than 15% of the M wave) compared with a normal mean of 39.5±13.0%. Overall abnormal MEPs (delayed, absent, or reduced in amplitude) approached 100%. It is argued that measuring central motor delay, which was not significantly different in the patients compared with normals, is subject to error in ALS.

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