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 .