Parkinson's disease is the second most common neurodegenerative disease, after Alzheimer's. It tends to present in patients older than 60, but there has been an increasing incidence in younger people, with up to 20% of patients being younger than 60 at diagnosis.
Studies have shown that Parkinson's effects begin years before clinical symptoms appear, but even when they do appear, they can be mistaken for other syndromes such as essential tremor or psychogenic movement disorders. In fact, misdiagnosis rates for Parkinson's have been estimated to be as high as 20% to 30%.
Traditionally, CT and PET have been used to diagnose and monitor Parkinson's disease, but these exams can be invasive and expensive and may not always be available. But in 1995, researchers using transcranial sonography discovered that hyperechogenicity of the substantia nigra -- a midbrain basal ganglia structure -- appeared in 90% of Parkinson's patients compared with 10% of healthy patients. This finding suggested a new way to identify Parkinson's even before clinical symptoms manifest, wrote the team led by Dr. Anyu Tao of Huazhong University of Science and Technology in Wuhan, China (Ultrasound Med Biol, March 2019, Vol. 45:3, pp 628-641).
"Since the first description of substantia nigra hyperechogenicity in Parkinson's disease patients ... transcranial sonography has now been widely accepted for the assessment of Parkinson's disease," the group wrote.
Transcranial sonography's benefits include its low cost, wide availability, noninvasiveness, and repeatability, the researchers noted. But the technique does have limitations, such as operator dependence and insufficient temporal bone window, which can occur in 5% to 20% of patients.
Tao and colleagues sought to explore the diagnostic accuracy of transcranial ultrasound in the detection of Parkinson's disease by conducting a systematic review and meta-analysis of literature published in the past 10 years. The researchers searched PubMed, Embase, and Cochrane Library databases from their inception to 2018, using appropriate keywords; 39 studies that included 6,641 patients met their inclusion criteria.
From their analysis, the researchers found that transcranial sonography had a sensitivity of 84% and a specificity of 85% for detecting Parkinson's when substantia nigra hyperechogenicity was used as the reference standard for the disease. In addition, in a subgroup analysis, the modality had a sensitivity of 85% and a specificity of 89% in differentiating Parkinson's disease patients from normal controls. Finally, transcranial sonography had a sensitivity of 82% and a specificity of 74% when it came to distinguishing Parkinson's from other syndromes.
Because substantia nigra hyperechogenicity is detectable in the early stages of Parkinson's, identifying it using transcranial sonography could give clinicians and their patients more options for dealing with the disease, according to Tao's group.
"We believe that transcranial sonography imaging should be the initial noninvasive assessment method for the diagnosis of Parkinson's disease," the researchers concluded.
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