Olfactory dysfunction occurrence, undetected hazards, and relationships in Parkinson’s disease: a multicentre study

Background The study sought to quantify and stratify olfactory dysfunction (OD) in Parkinson's disease (PD) using a brief multi-item tool and to explore demographic and clinical patterns in a broad cohort from Egypt. We conducted a multicentre cross-sectional study across neurology clinics. OD was assessed using Vernetti’s Hyposmia Rating Scale, which was translated into Egyptian, integrated into the study survey, piloted, and psychometrically tested. Analyses included multivariable adjusted models. Results We enrolled 434 patients with PD. Median age at diagnosis was 55 years (IQR 45 to 62), and two thirds were diagnosed within 1 year of motor symptom onset. Family history of PD (20%) was associated with motor symptoms appearing years earlier. Smoking, however, was associated with a later age. More than half of all patients had OD (58.5%), which was typically gradual and either persistent or worsening. The six-item scale identified 34.3% of OD cases that a single global question would have missed ( p < 0.001). In adjusted models, OD showed only a small association with education. A quarter of patients reported never detecting nearby gas leaks even when alerted. Loss of food-smell distinction closely tracked OD status ( p < 0.001). Most had at least one other non-motor symptom (NMS). Conclusions A majority of patients had OD. It was the prevailing NMS and correlated with overall burden. PD patients in this cohort had a younger age at disease onset and a high rate of family history linked to an even earlier onset. The interval from initial motor complaints to diagnosis appeared comparable to that reported in advanced healthcare settings worldwide. For hyposmia assessment, the brief scale improved identification and flagged safety risks and quality-of-life implications. The hyposmia-related hazards warrant further investigation to objectively test hazard detection and risk-reduction measures.