Specificity and sensitivity of transcranial sonography of the substantia nigra in the diagnosis of Parkinson's disease: prospective cohort study in 196 patients

Objective Numerous ultrasound studies have suggested that a typical enlarged area of echogenicity in the substantia nigra (SN+) can help diagnose idiopathic Parkinson's disease (IPD). Almost all these studies were retrospective and involved patients with well-established diagnoses and long-disease duration. In this study the diagnostic accuracy of transcranial sonography (TCS) of the substantia nigra in the patient with an undiagnosed parkinsonian syndrome of recent onset has been evaluated. Design Prospective cohort study for diagnostic accuracy. Setting Neurology outpatient clinics of two teaching hospitals in the Netherlands. Patients 196 consecutive patients, who were referred to two neurology outpatient clinics for analysis of clinically unclear parkinsonism. Within 2 weeks of inclusion all patients also underwent a TCS and a 123I-ioflupane Single Photon Emission CT (FP-CIT SPECT) scan of the brain (n=176). Outcome measures After 2 years, patients were re-examined by two movement disorder specialist neurologists for a final clinical diagnosis, that served as a surrogate gold standard for our study. Results Temporal acoustic windows were insufficient in 45 of 241 patients (18.67%). The final clinical diagnosis was IPD in 102 (52.0%) patients. Twenty-four (12.3%) patients were diagnosed with atypical parkinsonisms (APS) of which 8 (4.0%) multisystem atrophy (MSA), 6 (3.1%) progressive supranuclear palsy (PSP), 6 (3.1%) Lewy body dementia and 4 (2%) corticobasal degeneration. Twenty-one (10.7%) patients had a diagnosis of vascular parkinsonism, 20 (10.2%) essential tremor, 7 (3.6%) drug-induced parkinsonism and 22 (11.2%) patients had no parkinsonism but an alternative diagnosis. The sensitivity of a SN+ for the diagnosis IPD was 0.40 (CI 0.30 to 0.50) and the specificity 0.61 (CI 0.52 to 0.70). Hereby the positive predictive value (PPV) was 0.53 and the negative predictive value (NPV) 0.48. The sensitivity and specificity of FP-CIT SPECT scans for diagnosing IPD was 0.88 (CI 0.1 to 0.95) and 0.68 (CI 0.58 to 0.76) with a PPV of 0.75 and an NPV of 0.84. Conclusions The diagnostic accuracy of TCS in early stage Parkinson's disease is not sufficient for routine clinical use. Clinicaltrials.gov identifier NCT0036819