Sweet or Bland Dreams? Taste Loss in Isolated REM‐Sleep Behavior Disorder and Parkinson's Disease

Background Hyposmia and isolated REM sleep behavior disorder are well‐established features of prodromal Parkinson's disease (PD). Objectives The objective of the present study was to evaluate whether taste loss (reported in PD and possibly suggesting brain stem involvement) is present at the isolated REM sleep behavior disorder stage. Methods We assessed taste function using the Taste Strip Test (evaluating 4 concentrations of bitter, sweet, sour, and salty) in 44 participants with isolated REM sleep behavior disorder, 19 with PD, and 29 controls. All participants underwent video‐polysomnography, standardized questionnaires, and clinical examination, including olfactory assessment. Results Participants with isolated REM sleep behavior disorder and PD had lower taste scores than controls. There was no difference between isolated REM sleep behavior disorder and PD cohorts, nor was there any correlation between taste and olfaction, age, disease duration, cognition, or autonomic function. Conclusion This study demonstrates for the first time the presence of taste impairment in isolated REM sleep behavior disorder that is independent of olfactory dysfunction and comparable to participants with PD. © 2021 International Parkinson and Movement Disorder Society