Objective: Determine the neural basis of olfactory impairment in akinetic-rigid (PDAR) and tremor predominant (PDT) Parkinson’s disease subtypes. Methods: We combined resting-state fMRI (rs-fMRI) with seed based functional connectivity (FC) in order to delineate the olfactory network’s functional connectivity (ON FC) between PDAR and PDT patients. We then contrasted their ON FC patterns with cognitively normal (CN) subjects. All three groups were closely matched in age, demographic variables, and adjusted for relative cognitive performance. Olfactory function was measured using the University of Pennsylvania Smell Identification Test (UPSIT). Results: UPSIT scores were lower in akinetic-rigid vs tremor subtypes; ON FC values were lower in PDAR compared to PDT and CN, and followed the trend observed in UPSIT scores. UPSIT scores and ON FC values were significantly correlated, reflecting the effects of PD pathologies. Conclusions: The results show that olfactory function differs between PDAR and PDT suggesting a correlation between PD-related motor symptoms and olfactory deficits. ON FC differences accounts for the impaired olfactory functions observed between PDAR and PDT. PDAR is known to have worse clinical outcomes and faster cognitive decline compared to PDT; therefore, PD-related olfactory dysfunction may serve as a novel metric for enhancing PD prognosis.
bioRxiv Subject Collection: Neuroscience