Association of severe hyposmia and frontal lobe dysfunction in patients with Parkinson's disease.

BACKGROUNDS AND OBJECTIVES: Severe hyposmia (SH) is a prodromal symptom of dementia associated with Parkinson's disease (PD) caused by Lewy bodies deposited in the limbic regions that connect the frontal and temporal lobes. We aimed to clarify the association between hyposmia and frontal lobe dysfunction (FLD) among patients with PD.

METHODS: Patients with PD and Hoehn & Yahr stage 1-3 at on-periods without apparent dementia were screened. FLD was defined as a score of ≤14 on the Frontal Assessment Battery (FAB). SH was defined as an average recognition threshold >4 in the T&T Olfactometer. For each subscore, a recognition score of ≥4 was defined as SH. We examined whether SH and its subscores were associated with FLD and evaluated which FAB subscore might be lower in PD patients with SH using Poisson regression analysis with a robust variance estimator.

RESULTS: We included 189 patients (median age, 68 years; 107 [57 %] male). FLD was observed in 53 (28 %) patients. Multivariable analysis showed that SH (PR 1.789, 95 % confidence intervals (CI) 1.115-2.872, p = 0.016) was associated with FLD. Regarding odor domains, only SH for fruity smells was associated with FLD (PR 1.970, 95 % CI 1.306-2.972, p = 0.001). Patients with SH had a higher subscore only for FAB-1 (similarity [conceptualization], p = 0.030), indicating linguistically mediated executive dysfunction.

CONCLUSION: In patients with PD, SH is associated with FLD, especially with linguistically mediated executive dysfunction. Particularly, SH for fruity smells may be a sensitive indicator of FLD.