Objective: To characterize olfaction in a cohort of PD patients and to investigate the relationship between olfactory impairment with both motor and non-motor features and other clinical characteristics (duration, stage and severity).

Background: Olfactory dysfunction is one of the earliest and most frequent non-motor symptoms (prevalence>90%) in PD. However, hyposmia correlation with motor or other non-motor symptoms still lacks a full characterization[1].

Method: One-hundred fifty-four patients with idiopathic PD without dementia (Mini-Mental State Examination score >25) were included. Odor identification ability was tested using the validated Italian Olfactory Identification Test (33-testers), specifically designed for the Italian population[2]. A comprehensive spectrum of motor (tremor, bradykinesia, rigidity, postural stability, gait, masked face, speech, voice, posture) and non-motor features (urinary symptoms, depression, sleep disorders, constipation) was assessed. Patients were divided into 3 clinical phenotypes: tremor-dominant type (TDT), akinetic-rigid type (ART) and mixed type (MXT)[3].

Results: Hyposmia was found in 141/154 (93%) patients (mean Hoehn&Yahr (H&Y):1.99±0.6, mean Unified Parkinson’s Disease Rating Scale part III:23.4±11.56, mean age 66.96±9.2 years, mean disease duration 5.57±4.9 years). Hyposmic patients were older than those with normal olfaction (p=0.012). H&Y score≥2 was associated with a higher probability of being hyposmic (OR=1.18, p=0.01). IOIT score did not significantly differ between TDT, ART and MXT PD patients. IOIT score directly correlated with patients’ age (p<0.001), disease duration (p=0.01) and H&Y score≥2 (p<0.05). Clinical features associated with higher IOIT score were freezing of gait (FOG) (+2.38, p=0.027) and camptocormia (+2.31, p=0.022).

Conclusion: In our cohort, IOIT scores showed a correlation between hyposmia severity and axial motor signs, but not with non-motor symptoms. Assessing olfactory dysfunction through IOIT may help identify PD patients at higher risk of developing severe motor features (camptocormia and FOG). Overall, IOIT may be a useful tool not only for supporting PD diagnosis but also for providing prognostic information about motor function. Follow-up studies are warranted to confirm IOIT’s ability to predict motor symptoms progression in PD patients.

References: 1. Roos DS, Twisk JWR, Raijmakers P, Doty RL, Berendse HW. Hyposmia as a marker of (non-)motor disease severity in Parkinson’s disease. J Neural Transm (Vienna). 2019;126(11):1471-8.
2. Maremmani C, Rossi G, Tambasco N, Fattori B, Pieroni A, Ramat S, et al. The validity and reliability of the Italian Olfactory Identification Test (IOIT) in healthy subjects and in Parkinson’s disease patients. Parkinsonism Relat Disord. 2012;18(6):788-93.
3. M.C. Schiess, H. Zheng, V.M. Soukup, J.G. Bonnen, H.J.W. Nauta, Parkinson’s disease subtypes: clinical classification and ventricular cerebrospinal fluid analysis, Parkinsonism Relat. Disord., 6 (2) (2000), pp. 69-76

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MDS Abstracts - https://www.mdsabstracts.org/abstract/motor-and-non-motor-correlates-of-hyposmia-detected-by-the-italian-olfactory-identification-test-ioit-in-an-italian-cohort-of-parkinsons-disease-patients/