Population-Based and Routinely Collected Health Data Studies of Immunobullous Diseases: A Scoping Review

BACKGROUND: Validated case definitions are essential for reliable epidemiological research using routinely collected health data. The extent to which population-based studies on autoimmune blistering diseases (AIBDs) use validated case definitions is uncertain, and variability in definitions may limit the generalizability of findings. OBJECTIVE: To describe definitions of AIBDs used in population-based epidemiologic studies and whether these definitions have been validated. METHODS: MEDLINE and Embase were searched for epidemiologic studies on pemphigoid, pemphigus and their variants, dermatitis herpetiformis (DH), epidermolysis bullosa acquisita (EBA), and linear IgA bullous dermatosis (LABD). Eligible studies reported case definitions using routinely collected data. Two reviewers independently screened studies and extracted data, with discrepancies resolved by consensus. RESULTS: Ninety-two studies met the inclusion criteria. Among 63 pemphigoid studies, the majority used International Classification of Diseases (ICD) codes, and 26 studies validated case definitions using combinations of clinical diagnosis, histopathology, and direct or indirect immunofluorescence, often with scoring systems. The majority of 39 pemphigus studies used ICD codes or electronic medical records to identify cases; of the 5 studies that validated cases, most used chart review requiring 2 or more confirmatory clinical or laboratory findings. Two of 6 DH studies used validated definitions with clinical and immunopathological criteria. Among 8 EBA studies, none reported formal validation. One LABD study was included without case validation. CONCLUSION: Most population-based studies of AIBDs rely on administrative coding or electronic medical records, but few use formally validated case definitions. Improving and standardizing validation practices is important to enhance the accuracy and comparability of epidemiological findings in AIBDs.