Demographics, characteristics and medical treatment among adults with hand eczema in Denmark. A cross-sectional validation and registry-based study

<bold>Background: </bold>The international classification of diseases, 10th revision (ICD-10) includes several unvalidated diagnostic codes for hand eczema (HE). Knowledge is sparse on HE patient characteristics.<bold>Objectives: </bold>To validate selected HE ICD-10 codes in the Danish National Patient Registry (DNPR) and describe disease characteristics, lifestyle factors and medication use in adult HE patients.<bold>Methods: </bold>Nineteen HE ICD-10 codes were selected and validated based on patient charts. Five cohorts were constructed based on the diagnostic code, DL30.8H (HE unspecified), in the DNPR: (i) patients with DL30.8H code (n = 8386), (ii) patients with DL30.8H code, but without atopic dermatitis (AD) (n = 7406), (iii) sex- and age-matched general population (n = 8386) without HE. Two additional cohorts nested in the DNPR included participants from the Danish Skin Cohort, (iv) patients with DL30.8H code but without AD (n = 1340) and (v) general population cohort (n = 9876).<bold>Results: </bold>ICD-10 codes revealed positive predictive values >= 90% except irritant contact dermatitis (unspecified) (79.7%) and hyperkeratotic hand and foot eczema (84.1%). HE patients were most often women, middle-aged or older, of Danish ethnicity, had an atopic medical history and were smokers. Topical corticosteroid prescriptions were almost doubled in HE cohorts compared to general populations.<bold>Conclusion: </bold>We validated several HE ICD-10 codes and identified important HE patient characteristics.