The diagnostic value of transcranial sonography in Swedish parkinsonism patients: A retrospective cohort study with long-term follow-up.

Introduction: Although transcranial sonography (TCS) assessing hyperechogenic substantia nigra (SN+) as biomarker for Parkinsońs disease (PD) has been introduced elsewhere, the clinical relevance and accuracy in a Swedish population is still unknown. Methods: This retrospective single-center study included 74 patients with predominantly early-stage parkinsonism at first visit who had been examined by TCS from 2013 to 2017 to determine the SN+ biomarker status in relation to PD, atypical parkinsonian disorders (APS), essential tremor (ET) and vascular/secondary/ unspecified parkinsonism, with the aim of long-term follow-up to confirm the clinical diagnosis. The cut-off value for SN+ was regarded as the 90 % percentile of SN echogenicity in a local healthy cohort (here, 0.23 cm2). Results: In 2024, the mean follow-up time was 95 months. Three patients (4 %) without transcranial bone were excluded. SN+ was found in 38/51 patients with finally diagnosed PD and 4/20 patients with other final clinical diagnoses (p < 0.001). Sensitivity was moderate (75 %) whereas specificity and the positive predictive value were higher (80 % and 90 %, respectively). SN area measurements (most abnormal side) were significantly different in PD-patients compared to non-PD patients (n = 63; 0.28 ± 0.09 [95 % CI: 0.25-0.30] cm2 vs. 0.23 ± 0.10 [0.18-0.29] cm2, p 0.035). Conclusion: After a follow-up of up to 8 years, to maximize diagnostic certainty, our findings support the use of TCS as a valuable add-on tool in PD diagnostics in a Swedish patient population, already in the early stage of disease but not for screening.