Combined Transcranial Sonography of the Substantia Nigra and 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in the Diagnosis of Parkinson's Disease and Atypical Parkinsonian Syndromes.

BACKGROUND: Accurate differentiation between Parkinson's disease (PD) and atypical parkinsonian syndromes (APS) remains challenging where dual-tracer (11C-2β-carbomethoxy-3β-(4-fluorophenyl) tropane [[11C]CFT] and 18F-fluorodeoxyglucose [[18F]FDG]) positron emission tomography/computed tomography (PET/CT) access is limited. OBJECTIVE: The aim was to investigate whether transcranial sonography (TCS) of the substantia nigra (SN) can replace [11C]CFT PET when combined with [18F]FDG PET for diagnosing early PD and differentiating PD from APS. METHODS: Totally 160 patients with suspected PD or APS underwent clinical assessment, SN-TCS, and PET/CT. PET/CT images were evaluated by visual assessment based on predetermined disease-specific patterns. Diagnoses of TCS-SN were performed according to predefined criteria. Diagnostic performance was evaluated using 2 binary comparisons: PD versus non-PD and APS versus non-APS. RESULTS: After a median follow-up period of 23 months, the final clinical diagnoses were PD (n = 72), APS (n = 50), and parkinsonian syndromes other than PD or APS (n = 33). For diagnosis of PD, combined SN-TCS with [18F]FDG PET/CT strategy exhibited comparable specificity to dual-tracer PET/CT (90.4% vs. 95.2%, P = 0.344) but significantly lower sensitivity (34.7% vs. 84.7%, P < 0.001). Compared to TCS alone, the combined approach yielded similar sensitivity (34.7% vs. 36.1%, P = 1.000) and higher specificity (90.4% vs. 72.3%, P < 0.001). For APS diagnosis, this combined approach achieved comparable sensitivity (76.0% vs. 86.0%, P = 0.180), specificity (86.7% vs. 86.7%, P = 1.000), accuracy (83.2% vs. 86.5%, P = 0.302), and the area under the curve (0.81 vs. 0.86, P = 0.115) relative to dual-tracer PET/CT. CONCLUSION: The combination of SN-TCS and [18F]FDG PET/CT may serve as an effective triage tool for PD with high specificity. For APS, this combined strategy may provide a feasible diagnostic option in settings with limited access to dual-tracer PET/CT.