ABNORMAL Score for the Etiologic Triage of Parkinsonism: Development and Apparent Diagnostic Performance

Background: Etiologic differentiation of Parkinson disease (PD) from non-PD parkinsonism remains challenging early in the disease course.Movement disorder specialists integrate age at onset, clinical context, tempo, systemic manifestations, family history, neuroimaging, dopaminergic response, and early evolution, but this reasoning is not usually represented in a single bedside framework.We developed the ABNORMAL score to structure these eight diagnostic domains into an unweighted heuristic tool and evaluated its preliminary diagnostic performance.Methods: We conducted a retrospective cross-sectional derivation study including 102 patients evaluated in 2025 at a tertiary movement disorders clinic in Mexico City, whose etiologic diagnoses were assigned based on longitudinal clinical follow-up.Each domain was scored from 0 to 2 (total score range: 0-16).Prespecified probability zones were defined as 0-3 (probable PD), 4-6 (diagnostic gray zone), and ≥7 (probable non-PD parkinsonism).Receiver operating characteristic (ROC) curve analysis was performed to evaluate diagnostic discrimination.Results: The cohort comprised 73 patients (71.6%) with PD and 29 (28.4%) with non-PD parkinsonism.Mean ABNORMAL scores were 1.60±1.1 (range: 0-4) in PD and 6.69±1.4(range: 4-9) in non-PD cases.The apparent area under the ROC curve (AUC) was 0.994 (95% CI: 0.986-0.999).In this derivation cohort, the threshold of ≥4, selected using the Youden index in the same dataset to identify non-PD parkinsonism, yielded an apparent sensitivity of 100%, a specificity of 91.8%, a positive predictive value of 82.9%, a negative predictive value of 100%, and an overall accuracy of 94.1%.All six patients with PD who were classified as positive for non-PD parkinsonism scored exactly 4, within the proposed exploratory gray zone; no non-PD patient scored below 4.These same-cohort estimates may be subject to optimism bias and require external validation.Conclusions: The ABNORMAL score translates expert clinical reasoning into a reproducible, unweighted heuristic tool that suggests high preliminary diagnostic accuracy for differentiating PD from non-PD parkinsonism.It serves as a bedside decision-support tool to guide targeted investigation and longitudinal triage, pending prospective external validation.