Validity of First-Time Diagnoses of Darier’s Disease in the Danish National Patient Registry

PURPOSE: Darier's disease (DD) is a rare genetic skin disease, characterized by yellow-brown, scaly, crusted papules in seborrheic areas and specific nail changes. This study aimed to validate all first-time diagnoses of DD in Danish National Patient Registry (DNPR). The intent of the study is validation of DNPR for epidemiological and clinical studies on DD. PATIENTS AND METHODS: We identified all patients in DNPR who received their first-time diagnosis of DD between January 1, 1977 and December 31, 2018 (International Classification of Diseases [ICD]-8 code 75721 until the end of 1993: ICD-10 code Q828F thereafter). We restricted to diagnoses from departments of dermatology, where these patients are managed. We validated diagnoses against information from medical records, using predefined data extraction sheets and validation criteria. We classified diagnoses as probable when characteristic clinical features were present; confirmed when there was also genetic confirmation, histopathological confirmation and/or positive family history, or rejected (remaining patients). We estimated positive predictive values (PPVs) with 95% confidence intervals (CIs) for diagnoses overall and stratified by ICD classification, sex, age at diagnosis, year of diagnosis, type of diagnosis, and type of contact. RESULTS: We identified 277 first-time diagnoses of DD, of which 229 (82.7%) stemmed from departments of dermatology. Medical records were available for 196 (85.6%) of these. The overall PPVs for probable and confirmed DD were 89.3% (95% CI: 84.2–92.9) and 81.1% (95% CI: 75.1–86.0), respectively. The PPV for probable ICD-8 diagnosis (95.8% (95% CI: 82.1–99.5)) was slightly higher than that of probable ICD-10 diagnosis (88.4% (95% CI: 82.7–92.3)). CONCLUSION: The validity of first-time diagnoses of DD recorded by departments of dermatology in the DNPR is relatively high, making DNPR suitable for epidemiological studies on DD in Denmark, as well as a useful source for recruitment to clinical studies on DD.