Does the motor cortex influence denervation in ALS? EMG studies of muscles with both contralateral and bilateral corticospinal innervation

Objectives: To evaluate the pattern of degeneration of lower motor neuron progression in ALS in relation to the contralateral and ipsilateral corticospinal innervation of the tested muscles. Methods: EMG evaluation of the sternomastoid and trapezius muscles on one or both sides, and transcranial magnetic stimulation to record motor evoked responses from these muscles after ipsilateral and contralateral cortical stimulation. The sternomastoid muscle receives corticospinal input from both hemispheres, but the trapezius only a contralateral corticospinal innervation; however the power motor innervation of both these muscles is derived from the same spinal nucleus, and the same motor nerve. Seventy-five patients with ALS were studied at the time of diagnosis, and 54 control subjects, consisting of normal subjects and disease control subjects. MUP analysis and spontaneous activity were assessed. Results: We confirmed that the sternomastoid receives both contralateral and ipsilateral corticospinal innervation, and the trapezius usually only contralateral innervation. The MUP analysis revealed symmetric changes in sternomastoid and trapezius muscles, and both muscles were equally affected. Conclusions: Our findings are in accord with the concept that LMN degeneration in ALS is related to local factors in the spinal cord. Significance: Our findings suggest that local factors in the spinal grey matter are important in causing LMN degeneration in ALS, but they do not rule out a corticomotoneuronal contribution.