Clinical utility of DaTscan in clinically uncertain parkinsonian syndromes: a systematic review and meta‑analysis.

BACKGROUND: Clinically uncertain parkinsonian syndromes (CUPS) pose diagnostic challenges, particularly in distinguishing degenerative from non‑degenerative etiologies. DaTscan (123I-ioflupane SPECT) is frequently used to clarify ambiguity, but the magnitude of its diagnostic impact across different initial clinical suspicions remains unclear. METHODS: A systematic review of MEDLINE, EMBASE, PsycINFO, and the Cochrane Library was conducted from January 2002 to February 2026, with no language restrictions. Studies reporting a diagnostic change after DaTscan were included. Two reviewers independently performed screening, data extraction, and quality assessment using ROBINS‑I tool. Proportions were pooled using a random‑effects model with Restricted Maximum Likelihood. Exact Clopper-Pearson intervals were calculated. RESULTS: Seventy‑five observations comprising 2,232 patients were included. The pooled proportion of diagnostic revision was 0.32 (95 % CI 0.26-0.38; I2 = 80 %). Diagnostic changes were most frequent among patients initially suspected of vascular parkinsonism (0.53; 95 % CI 0.37-0.69; I2 = 55 %) and drug‑induced parkinsonism (0.38; 95 % CI 0.28-0.49; I2 = 38 %). Revisions also occurred in cases initially labeled as functional movement disorder (0.35; 95 % CI 0.23-0.49; I2 = 0 %), essential tremor (0.27; 95 % CI 0.18-0.38; I2 = 62 %), and Parkinson's disease (0.22; 95 % CI 0.17-0.33; I2 = 92 %). CONCLUSIONS: DaTscan was associated with diagnostic revision in approximately one‑third of patients with CUPS, with the greatest impact in vascular and drug‑induced parkinsonism. These findings support a role for DaTscan as an adjunct to clinical assessment when diagnostic uncertainty persists.