Hyperechogenicity of substantia nigra for differential diagnosis of Parkinson's disease: A meta-analysis

Studies have suggested that the majority of patients with Parkinson's disease have abnormal ultrasound hyperechogenicity of the substantia nigra, and that this may be useful in diagnosis. We performed a systematic review and meta-analysis to evaluate diagnostic value of substantia nigra ultrasound to differentiate Parkinson's disease from atypical parkinsonism and from essential tremor. We systematically searched PubMed and EMBASE for relevant studies published until November 2016. Eligible articles were screened, data were extracted and study quality was scored by two independent reviewers. We applied random effect models to calculate pooled estimates for the prevalence of hyperechogenicity in each condition. For final meta-analysis, 71 articles with a total number of 5730 participants (idiopathic Parkinson's disease: 4494, atypical parkinsonism: 594, essential tremor: 642) were included. The pooled prevalence rate of hyperechogenicity was 84% (95 %CI 80-87%) in idiopathic Parkinson's disease, 28% (95% CI 20-36%) in atypical parkinsonism and 15% (95% CI 7-23%) in essential tremor. Based on our meta-analysis, substantia nigra hyperechogenecity has 75% (95% CI: 60-86%) sensitivity and 70% (95% CI: 55-81%) specificity to differentiate idiopathic Parkinson's disease from atypical parkinsonism. Sensitivity and specificity to distinguish idiopathic Parkinson's disease from essential tremor was calculated as 78% (95% CI: 69-85%) and 85% (95% CI: 77-91%), respectively. Findings from our meta-analysis showed that transcranial sonography can provide useful information to differentiate idiopathic Parkinson's disease from mimicking movement disorders, although sensitivity and specificity are suboptimal, particularly for differentiating from atypical parkinsonism.