Olfactory Impairment Predicts Underlying Dopaminergic Deficit in Presumed Drug-Induced Parkinsonism

Drug-induced parkinsonism (DIP) is common, and the motor symptoms can be indistinguishable from Parkinson's disease (PD). When symptoms persist after drug withdrawal, this may represent "unmasking" of underlying PD. We previously reported that hyposmia, a common nonmotor feature of PD, was associated with persistent DIP. Here, we report on a series of 33 consecutive patients who underwent dopamine transporter imaging to evaluate DIP. We examined the clinical correlates of underlying dopaminergic denervation by comparing subjects with normal and abnormal scans. Imaging was abnormal in 7 of 33 (21%) cases. Motor features were similar in patients with normal and abnormal scans. Olfactory testing was available for 30 subjects and was concordant with imaging in 27 of 30 (odds ratio = 63; 95% confidence interval: 4.8-820; P = 0.002). Olfactory testing may be a simple screen to help identify DIP patients with underlying dopaminergic denervation, consistent with unmasking of incipient PD.