Detecting lower motor neuron dysfunction of the pharynx and larynx with electromyography

This study assessed the utility of clinical electromyography (EMG) for detecting lower motor neuron (LMN) or upper motor neuron (UMN) dysfunction affecting the intrinsic muscles of the larynx and pharynx. Twenty-nine subjects were examined; their clinical diagnoses included perioperative nerve injury, cerebral infarction, and lateral medullary infarction. Resting activity, motor unit action potential (MUAP) morphology, and MUAP recruitment were evaluated in every case. Medical records (excluding EMG data) were analyzed for clinical evidence of LMN or UMN dysfunction in the intrinsic muscles of the larynx and pharynx. The diagnosis of LMN dysfunction rested on clinical data consistent with cranial nerve injury, poliomyelitis, Wallenberg syndrome, or unilateral bulbar palsy. Criteria for UMN dysfunction included previous cerebral (not brainstem) infarction or mass lesion or the presence of hemiparesis. Electromyographic abnormalities were significantly associated with LMN dysfunction (p less than .05), but they were not significantly associated with UMN dysfunction. Of the parameters tested, MUAP recruitment was the most sensitive (82%) and specific (92%).