Effect of Levodopa + Carbidopa on the Laryngeal Electromyographic Pattern in Parkinson Disease

Summary Background Vocal impairment is one of the main debilitating symptoms of Parkinson disease (PD). The effect of levodopa on vocal function remains unclear. Objective This study aimed to determine the effect of levodopa on electromyographic patterns of the laryngeal muscle in patients with PD. Study design This is a prospective interventional trial. Methods Nineteen patients with PD—diagnosed by laryngeal electromyography—were enrolled. Cricothyroid and thyroarytenoid (TA) muscle activities were measured at rest and during muscle contraction (phonation), when participants were on and off medication (12 hours after the last levodopa dose). Results Prevalence of resting hypertonia in the cricothyroid muscle was similar in the off and on states (7 of 19, P  = 1.00). Eight patients off medication and four patients on medication had hypertonic TA muscle at rest ( P  = 0.289). No electromyographic alterations were observed during phonation for either medication states. Conclusion Despite a tendency for increased rest tracings in the TA muscle when participants were on medication, no association was found between laryngeal electromyography findings and levodopa + carbidopa administration.