Relation between Olfactory Dysfunction and Episodic Verbal Memory in Early Parkinson's Disease

Abstract

Introduction: Olfactory dysfunction is an early and common symptom in idiopathic Parkinson's disease (IPD). Recently, the relation between olfactory dysfunction and cognitive loss in IPD has been reported. In our study, we aimed to investigate the relation between olfactory dysfunction and cognitive impairments in early IPD related with this theory.

Methods: In this study, we included 28 patients with stage 1 and stage 2 IPD according to the Hoehn-Yahr (H-Y) scale and 19 healthy participants. The University of Pennsylvania Smell Identification Test (UPSIT) was performed for evaluating olfactory function. For cognitive investigation in participants, the clock drawing test, Stroop test, verbal fluency test, Benton face recognition test (BFR), Benton line judgment orientation test (BLO), and Auditory Verbal Learning Test (AVLT) were performed.

Results: We found significantly lower UPSIT scores in the patient group compared to controls (p=0.018). In the neuropsychological investigation, only Stroop test and BLOT test scores were significantly lower in the patient group compared to controls (p=0.003, p=0.002, respectively). We found a negative correlation between UPSIT scores and Stroop time (p=0.033) and Stroop error (p=0.037) and a positive correlation between UPSIT scores and SBST long-term memory scores (p=0.016) in patients.

Conclusion: In our study, we found mild cognitive impairment related with visuospatial and executive functions in early-stage IPD compared to controls. But, in the patient group, we detected a different impairment pattern of memory and frontal functions that correlated with hyposmia. This different pattern might be indicating a subgroup of IPD characterized by low performance in episodic verbal memory, with accompanying olfactory dysfunction in the early stage.