Transcranial magnetic stimulation in amyotrophic and primary lateral sclerosis

Conduction of the central motor pathways after transcranial magnetic stimulation (TMS) was investigated in 7 patients with amyotrophic lateral sclerosis (ALS) and 1 case with primary lateral sclerosis (PLS). Threshold intensity, central motor conduction time (CMCT) and amplitude of the motor evoked potentials (MEPs) were evaluated. Threshold was abnormal in 85% of tested limbs, and CMCT prolonged and amplitude of the MEPs attenuated in 28.5% of patients with ALS. Abnormal CMCT was asymmetric and related to clinical score. MEPs were absent in lower limbs in PLS, with prolonged or attenuated amplitude of the MEPs in upper limbs. EMG showed widespread signs of lower motor neuron involvement in ALS, but not in PLS. Cranial MRI showed frontoparietal cortical atrophy, more marked in pre-central gyrus, and SPECT there was lower tracer uptake in the perirolandic area in the PLS patient. EMG examination, TMS, cranial MRI and SPECT can help in the diagnosis of PLS.