Case Definitions and Data Sources for NNCSS Parkinson Disease Surveillance: A Systematic Review

The National Neurological Conditions Surveillance System (NNCSS) is congressionally mandated to track the epidemiology of neurological conditions in the United States. Parkinson disease (PD) was selected as an initial condition, but methods for conducting PD surveillance are limited.

To review evidence for, evaluate the performance of, and select data source types and case definitions for national PD surveillance.

Medline, Embase, PsycInfo, CINAHL, and Scopus were searched from January 1980 through November 2023; expert-identified and bibliographically mined references were included. Articles were screened and reviewed for eligibility from April 2020 to May 2024. Eligible articles included case definitions to produce population-based estimates and used data sources appropriate for population-level analyses. Study quality was assessed using Methodological Evaluation of Observational Research and Quality Assessment of Diagnostic Accuracy Studies-2. Case definitions and data source types were evaluated using key attributes of public health surveillance systems (hereafter key attributes).

A total of 156 articles, published between 2001 and 2023, were included. These articles largely used administrative data (140 [90%]), especially claims (102 [65%]). The 163 included case definitions varied substantially and were allocated into 6 groups along a spectrum according to likely inclusion and/or exclusion of other parkinsonisms (OP) and resulting misclassification bias. At one end, "PD probable" definitions (15 of 163 [9%]) removed most OP, maximizing specificity but likely missing some PD cases with limited or conflicting claims evidence. Alternatively, "PD possible" definitions (11 of 163 [7%]) captured PD cases with limited or conflicting evidence, maximizing sensitivity but likely including some OP. Case definitions' performance on key attributes varied widely. Claims performed best on key attributes.

In this systematic review of PD case definitions for national surveillance, no single definition provided a precise estimate due to potential diagnostic uncertainty in PD's early stages and International Classification of Disease (ICD) coding limitations that preclude definitively distinguishing PD from OP in population-based data sources. The best-performing PD probable and PD possible case definitions were selected to use to establish an estimate range. The probable definition provides high diagnostic certainty of PD. The possible definition avoids missing PD cases with limited or conflicting evidence. This work demonstrated NNCSS's methods for selecting and reappraising case definitions and data source types, providing a foundation for NNCSS's PD surveillance and expansion to other neurological conditions.