Biphasic (Subtherapeutic) Levodopa-Induced Respiratory Dysfunction in Parkinson Disease.

ABSTRACT

OBJECTIVE: To evaluate 3 cases illustrating a rarely recognized phenotype of Parkinson disease (PD), namely, biphasic levodopa-induced respiratory dysfunction manifesting as dyspnea. METHODS: To appreciate the nature of the fluctuations of respiratory function in response to levodopa, we measured changes in respiratory muscle control before and after the best therapeutic response to levodopa in 3 PD patients with fluctuating dyspnea. RESULTS: Episodes of breathlessness were accompanied by shallow tachypnea and reduced respiratory muscle control, as measured by maximal expiratory pressure, peak cough flow, and forced expiratory volume in 1 second. CONCLUSIONS: The spectrum of respiratory dysfunction in PD includes a biphasic reduced respiratory muscle control accompanying periods when the effect of levodopa is subtherapeutic. This biphasic levodopa-related complication represents a rarely recognized nonmotor phenomenon in PD. Management requires increasing the levodopa dose, shortening the interdose interval, or implementing a program of continuous dopaminergic stimulation.