Objective: To evaluate the diagnostic validity of PD identification in a national drug reimbursement registry requiring neurologist-confirmed diagnoses.

Background: Administrative healthcare databases are widely used in PD epidemiology and health services research, but their reliability depends on diagnostic accuracy. Previous validation studies of register-based PD identification have shown considerable variability, and few have assessed both sensitivity and specificity against long-term clinical diagnoses. In Finland, reimbursement for antiparkinsonian medication requires a neurologist-certified PD diagnosis and a formal statement submitted to the national insurer, creating a structured framework for registry-based case identification.

Method: We analyzed the Turku PD Cohort including 1626 patients diagnosed with PD between 2006 and 2020 in specialist care. Diagnoses were re-evaluated through detailed chart review after a median follow-up of approximately 10 years. Two movement disorder specialists independently classified final diagnoses based on clinical records, imaging, and treatment data. Registry linkage identified patients granted reimbursement for antiparkinsonian medications under ICD-10 code G20. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated using the final clinical diagnosis as the reference.

Results: Of the 1626 patients, 1550 (95.3%) had received reimbursement for PD medications. After long-term follow-up, 1314 were confirmed as PD and 236 reclassified to alternative diagnoses. Registry identification showed high sensitivity (98.2%) and PPV (84.8%). Only 24 confirmed PD cases (1.8%) were not captured. Diagnostic revisions most commonly reflected atypical or secondary parkinsonian syndromes. Specificity was lower (18.1%), reflecting diagnostic evolution during follow-up rather than systematic miscoding. The median delay between diagnosis and registry entry was 24 days.

Conclusion: A reimbursement registry requiring neurologist-confirmed diagnoses enables highly sensitive PD case identification with good PPV for epidemiological research. However, diagnostic evolution in early parkinsonism limits specificity in cross-sectional register data. Registry studies should therefore apply follow-up exclusion algorithms for alternative parkinsonian diagnoses.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/diagnostic-validity-of-pd-identification-in-a-neurologist-certified-national-drug-reimbursement-registry/