Diagnostic performance of the SASIT kit for Parkinson’s disease patients in Thailand

Abstract

Olfactory dysfunction is found in 75-90% of patients in the early stages of Parkinson's disease (PD). Despite its widespread occurrence in PD, many patients remain unaware of their olfactory dysfunction until they undergo standardized smell testing. The self-administered smell identification test kit (SASIT kit) was developed for use in diagnosing olfactory dysfunction in Thai individuals. This study aims to evaluate the diagnostic performance of the SASIT kit in differentiating PD patients from healthy individuals. This observational, cross-sectional diagnostic accuracy study was conducted at the outpatient departments of Pattani Hospital and Songkhla Hospital. Age-matched healthy volunteers who could perceive the normal n-butanol threshold, and Parkinson’s disease patients with Hoehn & Yahr Stage (H&Y stage) 1-3, aged 50 years and older, were included. The study was conducted between January and October 2024. Participants were screened using PHQ-2/PHQ-9, MMSE-Thai 2002, and anterior rhinoscopy. Subsequently, they performed the self-administered smell identification test (SASIT), and the SASIT scores were recorded.  Baseline clinical characteristics and SASIT scores (n, %, mean ±SD, or median [IQR]) were compared using a t-test. Diagnostic accuracy was assessed using the area under the receiver operating characteristic (ROC) curve. The optimal SASIT score cutoff for distinguishing PD patients from healthy volunteers was determined and presented with sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy. The study included 60 PD patients (mean age 67.6±7.9 years) and 60 healthy volunteers (mean age 69.5±10.9 years) with mean SASIT scores of 9.2±3.6 and 13.7±1.9, respectively (p<0.001). The SASIT kit showed an AuROC of 0.88 (95% CI: 0.82, 0.94). A cut-off score of ≤13 yielded 79.2% accuracy in differentiating PD patients from healthy individuals, with 90.0% sensitivity and 68.3% specificity. Therefore, the SASIT kit can be used as part of a multimodal diagnostic approach alongside clinical evaluation for diagnosing PD. Further studies with broader population samples are recommended to validate and expand upon the results gained by this study.