The contribution of trapezius and sternocleidomastoideus motor evoked potentials in the diagnosis of amyotrophic lateral sclerosis.

OBJECTIVE

We aimed to evaluate the role of corticobulbar motor evoked potentials (MEPs) as an objective electrophysiological measure to support clinical assessment of upper motor neurons in amyotrophic lateral sclerosis (ALS).

METHODS

Seventy-three patients with ALS and 44 healthy individuals with similar age and sex underwent transcranial magnetic stimulation with MEP recordings from the sternocleidomastoideus (SCM), trapezius, and abductor pollicis brevis muscles. Corticobulbar involvement was defined by prolonged cortical MEP latency or central motor conduction time (CMCT) or absence of MEP responses. Awaji-Shima diagnostic categories were evaluated before and after the incorporation of corticobulbar MEP abnormalities.

RESULTS

Corticobulbar MEP abnormalities were significantly more frequent in patients with ALS than in controls. Prolonged SCM-MEP latency and CMCT were the most sensitive electrophysiological markers of corticobulbar involvement. When interpreted alongside clinical upper motor neuron signs, corticobulbar MEP abnormalities facilitated upward diagnostic reclassification within the Awaji-Shima framework. One-fifth of patients who were initially classified as possible or probable ALS were reclassified as probable ALS and definite ALS, respectively, following inclusion of SCM- and trapezius-MEP abnormalities.

CONCLUSIONS

Corticobulbar MEP assessment provides objective electrophysiological support for upper motor neuron dysfunction and enhances diagnostic sensitivity when used in conjunction with the Awaji-Shima diagnostic framework.

SIGNIFICANCE: This study demonstrates that electrophysiological assessment of the corticobulbar pathway using SCM- and trapezius-MEPs provides objective evidence of upper motor neuron dysfunction in ALS.