Olfaction and apathy in early idiopathic Parkinson's disease

Background: Apathy remains a disabling symptom in Parkinson's disease (PD) with limited therapeutic success. Processing of emotions and smell share neuroanatomical and evolutionary pathways. Objectives: To explore the association of apathy with smell dysfunction (SD) in early PD. Methods: We analyzed patients with de-novo PD, with follow-up of at least 5 years from the Parkinson's Progression Markers Initiative. SD and apathy were defined using University of Pennsylvania Smell Identification Test and MDS-UPDRS part 1A. Odds ratios were calculated between apathy and olfaction groups. Kaplan-Meier survival analysis was grouped by presence/ absence of smell dysfunction. The Log Rank test was used to compare time to apathy. Results: We found no association between presence of apathy in patients with and without SD (OR 1.01 [0.49–2.08]). There was no significant difference between PD patients with and without SD in time to apathy (p = 0.72). Conclusions: SD does not portend greater risk of apathy in PD.