Objective: To investigate whether the absence of the swallow tail sign can be applied for distinguishing PD patients from healthy individuals.

Background: With conventional MRI, no Parkinson’s disease (PD)-specific abnormalities can be detected. However, there is a critical need for accompanying neuroimaging markers to guide diagnosis.
With high-resolution susceptibility-weighted MRI sequences, the imaging of nigrosome-1 is possible. In healthy individuals, the hyperintense nigrosome-1 is located in the posterior third of the substantia nigra corresponds to a linear shape and is surrounded by hypointense areas at frontal and lateral portions. This configuration is reminiscent of a swallow-tail, which is why it is also referred to as the swallow-tail sign.

Method: Thirty-seven PD patients (female/male: .54; mean age: 70 ± 7.2 years) and 35 age- and gender-matched healthy controls (female/male: .46; mean age: 70 ± 6.6 years) were investigated using a 3T MRI scanner (Siemens Skyra, 64 channel head coil). MR images were acquired with a magnetization transfer prepared dual-echo gradient-echo sequence. A trained neuroradiologist blind-rated the images and evaluated whether the swallow tail sign was absent on (i) both or at least (ii) one side of the participant’s midbrain.

Results: Contingency tables and chi-square tests were calculated as implemented in SPSS 26. Neither for condition (i) (X² (1, n=72) = .326, p=.568) nor for condition (ii) X² (1, n=72) = 1.595, p=.154) any relevant group difference between PD patients and healthy controls were present. Sensitivity for condition (i) is 37.8% and for condition (ii) 45.9%. Specificity for condition (i) is 68.6% and for condition (ii) 68.6%. In summary, the area under the receiver operating characteristics curve for condition (i) is .532, and for condition (ii) .573.

Conclusion: Even though previously stated by other research groups, our study does not provide evidence for the potential use of the swallow-tail sign as a supportive neuroimaging marker for the diagnosis of Parkinson’s disease. In conclusion, there is a critical need for improvements of substantia nigra targeted MRI sequences and the development of advanced segmentation algorithms.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-clinical-significance-of-the-swallow-tail-sign-in-distinguishing-parkinsons-disease-patients-from-healthy-individuals/