Objective: To asses the role of transcranial sonography in suspected drug-induced parkinsonism.

Background: Differential diagnosis between drug-induced parkinsonism (DIP) and Parkinson’s disease (PD) is challenging, as 15% of suspected DIP are actually PD unmasked by drug exposure. Substantia nigra hyperechogenicity (SN+) as detected with transcranial sonography (TCS) has proved useful for PD diagnosis. In a previous study (n:60), we assessed the role of TCS in suspected DIP, obtaining a positive predictive value (PPV) of SN+ of 49.9% for underlying PD. We hypothesized a longer follow-up could increase the PPV if more incidental PD cases were registered.

Method: At the end of the previous study 16 patients had PD diagnosis, and 44 DIP (7 SN+, 37 SN-), being clinical resolution after drug withdrawal the diagnostic gold standard. 44 DIP patient’s records were analysed 5 years after the completion of the study.

Results: After a mean follow up of 2.1 years (0-5), incidental PD diagnosis occurred in 2 SN+ patients (28.6%) and 1 (2.7%) SN-. Ten patients died (1 SN+, 9 SN-). Accuracy of SN+ to distinguish PD from DIP improved in terms of sensitivity 88% (82.4%), specificity 88 % (previous 85.4%) and PPV 54.5% (49.9%); with similar negative predictive value 96.2% (96.5%), area-under-the-curve 0.83.The hazard ratio for final PD diagnosis in SN+ subjects with suspected DIP was 11.4 (95% confidence interval 3.7-34.8, p<0.0002).

Conclusion: This study strengthens the role of TCS in the assessment of suspected DIP, not only for differential diagnosis but also as a prognostic tool. In our study, PPV of SN+ improved by 5%, even if follow-up was potentially insufficient in some patients

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MDS Abstracts - https://www.mdsabstracts.org/abstract/substantia-nigra-echogenicity-as-a-predictor-of-drug-withdrawal-response-in-suspected-drug-induced-parkinsonism-a-five-year-follow-up-study/