Prospective Randomized Controlled Trial of the Impact of Olfactory Training on Cognitive and Emotional Function in Individuals with Parkinson Disease

To investigate the clinical effects of olfactory training (OT) on olfactory function and related nonmotor symptoms in patients with Parkinson disease (PD).

Randomized controlled trial with a duration of 6 months of follow-up.

A tertiary hospital providing neurology rehabilitation services in China.

Of 81 initially recruited PD patients, 70 completed the study (N=70, 35 per group after randomization: OT group n=35, control n=35). All participants met inclusion criteria and received standard medical care. No dropouts were because of adverse effects.

The intervention group received OT using a standardized protocol. The training involved daily exposure to specific odorants for 6 months. The control group did not receive OT.

Primary outcomes included changes in olfactory test scores, memory and cognition scores (assessed using neuropsychological tests), and depressive and anxiety scale scores. These were measured before and after the 6-month intervention.

After 6 months, the intervention group exhibited significant improvements in olfactory test scores (threshold-discrimination-identification score: t=3.839, P<.01, Cohen's d=0.649), memory (memory quotient: t=2.597, P<.05, Cohen's d=0.439) and cognition scores (Mini-Mental State Examination: z=-2.791, P<.01, rank-biserial correlation (r)=-0.330 and Montreal Cognitive Assessment: t=2.626, P<.05, Cohen's d=0.444), depressive (Hamilton Depression Scale: z=-3.601, P<.001, r=-0.425 and Patient Health Questionnaire-9: z=-2.396, P<.05, r=-0.29) and anxiety (Hamilton Anxiety Scale: z=-3.049, P<.01, r=-0.36 and Generalized Anxiety Disorder-7: z=-2.849, P<.01, r=0.336) scale scores compared to the control group, showing moderate effects, respectively. The increase in memory scale scores was positively correlated with the increase in olfactory scores (Spearman r=0.415, P<.05). Statistical analysis was performed using SPSS 27.0 software, with P values indicating significance.

The OT has beneficial effects on olfactory function and related nonmotor symptoms in patients with PD. The 6-month training led to significant improvements in memory, cognition, depression, and anxiety. Further studies are needed to determine the long-term effects and optimal duration of OT for patients with PD.