Objectives: Substantia nigra hyperechogenicity (SN+) detected by transcranial ultrasound (TUS) is useful for Parkinson's disease (PD) diagnosis. Approximately 15% false negative results of unknown significance are reported. However, most TUS studies are transversal, and diagnosis of PD may change during follow-up.
Methods: Analysis of our prospective registry of TUS in clinical practice, selecting patients with sufficient bone window, to whom TUS was performed because of suspected PD, and a minimum of 3-year follow-up. Subjects were classified regarding SN echogenicity (SN+/SN-).
Results: 172 patients (122 SN+, 50 SN-), mean age 71 years (25-90), were included. At the end of follow-up, PD diagnosis was retained by 91% SN+ vs. 54% SN- subjects (p < 0.0001), while final diagnosis of atypical parkinsonism (3%SN+ vs. 16%SN-, p:0.0059) was more frequent in SN-. Dopaminergic therapy response was associated with SN+ (88% SN+ vs. 50% SN-, p < 0.0001), as were abnormal DaTSCANs (90%SN+ vs. 56%SN-, p 0.0027). SN echogenicity had 80% sensitivity and 68% specificity for PD diagnosis, while SPECT had 91% and 73%, respectively. SN+ was the only baseline predictor of keeping PD diagnosis at the end of follow-up, with an odds ratio of 12 (95% CI 3-42) (p < 0.001).
Conclusions: In our sample of patients with suspected PD, SN hyperechogenicity predicted PD diagnosis in the long term with a high odds ratio. Conversely, a baseline normal SN echogenicity was associated with a poorer response to PD therapy and change to a different diagnosis from PD. Normal SN appears to be a caveat for clinicians to check for atypical parkinsonism features during follow-up.
Keywords: Atypical Parkinsonism; Diagnosis; Essential tremor; Non-motor symptoms; Parkinson’s disease; Substantia nigra echogenicity; Transcranial ultrasound.