Biphasic (Subtherapeutic) Levodopa-induced Respiratory Dysfunction in Parkinson Disease

ABSTRACT Objective To evaluated three 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 three 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 (MEP), peak cough flow (PCF), and Forced Expiratory Volume in 1 second (FEV1). 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 non-motor phenomenon in PD. Management requires increasing the levodopa dose, shortening the interdose interval, or implementing a program of continuous dopaminergic stimulation.