Selective umami taste impairment in anosmic Parkinson's disease: associations with non-motor symptoms.

BACKGROUND AND PURPOSE: Olfactory dysfunction (OD) is a well-established prodromal feature of Parkinson's disease (PD). However, the association between olfactory loss and gustatory alterations - particularly umami perception - and their relationship with non-motor symptoms (NMS), affective status, reward-related eating behavior, and quality of life (QoL) remain incompletely characterized. The purpose of this study was to investigate the relationship between objectively defined anosmia and taste perception, NMS, mood disturbances, reward-driven eating behavior, and QoL in patients with PD.

METHODS: This cross-sectional study included 150 patients with idiopathic PD. Olfactory function was assessed using the Brief Smell Identification Test (BSIT). Patients with self-reported complete olfactory loss and BSIT scores ≤8 were classified as anosmic (n = 75), while the remaining patients were classified as non-anosmic (n = 75). Gustatory perception of the five basic tastes (sweet, sour, salty, bitter, and umami) was evaluated using visual analogue scales (VAS). Reward-related eating behavior was assessed using the Palatable Eating Motives Scale (PEMS), Food Cravings Questionnaire-Trait (FCQ-T), and Power of Food Scale (PFS). Non-motor symptom burden was evaluated using an olfaction-adjusted Non-Motor Symptoms Scale (NMSS Total*). Mood, anxiety, and QoL were assessed using the Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), and Parkinson's Disease Questionnaire-39 (PDQ-39).

RESULTS: Anosmic patients demonstrated significantly lower umami VAS scores compared with non-anosmic patients (p = 0.018), while no significant differences were observed for the other basic taste modalities. NMSS Total* scores were numerically higher in the anosmic group, with significantly greater impairment in the Mood/Cognition and Sexual domains. Depressive symptom severity was significantly higher in anosmic patients (p = 0.023). Although total PDQ-39 scores did not differ between groups, the Mobility and Cognition subdomains were significantly more impaired in anosmic patients. A weak negative correlation was observed between salty taste perception and depressive symptom severity.

CONCLUSION: The findings indicate that anosmia in PD is selectively associated with impaired umami taste perception and increased involvement of specific non-motor symptom domains, particularly affective and motivational features, suggesting a distinct chemosensory-related non-motor symptom profile. In PD, objectively defined anosmia is associated with selective umami taste impairment and increased depressive and non-motor symptom burden, indicating that chemosensory dysfunction reflects a clinically relevant non-motor symptom profile.