Epidemiology of prurigo nodularis in England: a retrospective database analysis.

Background: Prurigo nodularis is a debilitating skin condition that is classified as rare by the Genetic and Rare Diseases Information Center (GARD) and the National Organization for Rare Diseases (NORD). There are currently no estimates of the prevalence of prurigo nodularis in England.

Objectives: We aimed to address this data gap by describing the epidemiology of prurigo nodularis in a representative dataset derived from the English National Health Service.

Methods: The study utilized data from the Clinical Practice Research Datalink linked to Hospital Episode Statistics inpatient data. Patients with a diagnosis of prurigo nodularis were selected by clinical code in the primary care or inpatient datasets. Case definition was based on a minimum of two distinct diagnoses to maximize specificity. Point prevalence was calculated for the midpoint of 2018 and incidence rates from 2008 to 2018 were presented. For those classified as incident cases, demographic and clinical characteristics were reported. In sensitivity analyses the case definition was modified to relax the multiple diagnosis criteria and to restrict cases to those diagnosed within a maximum of 4 or 10 years of the midpoint prevalence date.

Results: Overall, 11 656 patients within the dataset had at least one prurigo nodularis diagnosis. Following application of the relevant inclusion criteria, 2743 patients formed the point prevalent cohort; the estimated prevalence was 3·27 patients per 10 000 population [95% confidence interval (CI) 3·15-3·40]. In sensitivity analyses the estimated prevalence ranged from 2·24 (95% CI 2·14-2·34) to 6·98 (95% CI 6·80-7·16). Incidence over the study period was 2·88 per 100 000 patient-years. Comorbidity was relatively high in this population, notably for atopic dermatitis (52·2%), depression (41·1%) and anxiety (35·4%).

Conclusions: This study supports the NORD/GARD classification of prurigo nodularis as a rare disease with a prevalence of 3·27 patients per 10 000 population, which equates to 18 471 patients living with the disease in England in 2018. The relatively high prevalence of comorbidity observed for these patients may increase the complexity of management.