Swallow Tail Sign on MRI—Is It Useful in a Diagnostic Workup in Drug‐Naïve Parkinson's Disease?

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ABSTRACT Background and Purpose To evaluate the diagnostic value of the Swallow Tail Sign (STS) on MRI as a paraclinical marker to support the initial diagnosis of early Parkinson's disease (PD). The STS is a hyperintense area in the substantia nigra pars compacta, observable in the healthy population, but absent in advanced PD. To our knowledge, no studies have investigated the STS presence in newly diagnosed, drug‐naïve PD. Methods Axial 3D gradient echo susceptibility‐weighted angiography 3‐T sequences of 35 patients with clinically confirmed drug‐naïve PD and 35 age‐matched healthy controls were independently reviewed by an experienced neurologist and a neuroradiologist. Unilateral or bilateral STS absence constituted a PD rating. Accuracy was assessed against clinical diagnosis as the gold standard. Results The inter‐rater agreement was substantial across all subjects (Cohen's kappa = 0.63). The association between the clinical diagnosis and the raters’ assessment was statistically significant ( p < 0.0001). The average diagnostic accuracy between the raters was 80.1% (sensitivity 82.4% and specificity 77.9%). The same 22 healthy controls and 24 PD patients were correctly classified in independent assessments without a joint consensus reading. Conclusions We observed the STS appearance of the healthy nigrosome‐1 in the healthy controls, and its predominant absence in the PD cohort. Due to the presence of false positives, we cautiously advocate its potential as a clinically useful additional tool, which, in conjunction with other biomarkers, can improve the diagnostic workup of early PD. The methodology allows for replication in clinics with no access to nuclear medicine facilities or high‐resolution 7‐T scanners.

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