Idiopathic Papular Dermatitis in the Spectrum of Chronic Papular Eruptions (Subacute Prurigo): Reappraisal and Diagnostic Algorithm

Background: The clinical diagnosis of papular eruptions is common but poorly characterized in the literature and the etiology is often unknown. Objective: To characterize the entity of idiopathic papular dermatitis in the spectrum of chronic papular eruptions. Methods: The cohort consisted of patients who presented at a tertiary medical center in 2005–2014 with a papular eruption of at least 4 months’ duration. Findings on histological analysis and thorough clinical investigation, performed in all cases, were collected. The patients completed a questionnaire on disease course and outcome. Results: Sixty-five patients were included. Sixteen patients showed morphological changes over time and were excluded. Investigations in the remaining 49 patients with a consistent papular morphology yielded a well-defined diagnosis in 23 (46%). Twenty-six patients (54%; 14 male) were diagnosed with idiopathic papular dermatitis. Their mean age at onset was 61.6 ± 14.4 years and the mean duration of disease 3.11 ± 2.726 years. In 60%, the rash resolved with conservative treatment during follow-up (mean 4.35 ± 2.53 years). Conclusions: Chronic papular eruptions encompass a wide range of skin diseases. In more than half of the cases, the etiopathogenesis remains unclear. On the basis of our results, we propose a diagnostic algorithm for idiopathic papular dermatitis.