Biological and psychosocial factors associated with the persistence of pruritus symptoms: protocol for a prospective, exploratory observational study in Germany (individual project of the Interdisciplinary SOMACROSS Research Unit [RU 5211])

INTRODUCTION: Chronic pruritus (CP) is a symptom of dermatologic, neurologic, systemic and psychosomatic diseases. CP has a prevalence of ~20% in the general population and is therefore a significant burden on society, but the transition from acute pruritus to CP is not well understood. It probably involves interactions between biological and psychosocial factors and pruritus-specific risk factors as well as mechanisms shared with other persistent somatic symptoms addressed in other projects of the SOMACROSS Research Unit (RU). Here we aim to identify psychosocial and biological factors and their interactions which might be associated with the persistence of CP with and without immunologic/inflammatory origin, that is, atopic dermatitis and pruritus on non-inflamed skin. We expect that psychosocial factors relevant to the persistence of symptoms such as fatigue and pain may also show associations to CP. METHODS AND ANALYSIS: In this prospective, exploratory observational study situated in Germany, three cohorts of 40 patients each with acute exacerbation of atopic dermatitis and chronic atopic dermatitis and 40 CP patients with unaffected skin will be recruited for a comprehensive translational investigation including pruritus-specific and the shared psychosocial assessments of the RU SOMACROSS. Pruritus-specific measures will include questionnaires, quantitative sensory testing, cutaneous nerve fibre morphology, skin barrier morphology, epidermal metabolism and pruritogen blood levels. Within 1 year, patients and 80 age-matched and sex-matched healthy controls will be examined at three time points, allowing cross-sectional comparison and a longitudinal investigation of predictive outcome factors in patients under treatment according to existing guidelines. ETHICS AND DISSEMINATION: The study has been approved by the ethics committees of Hamburg (2020-10200-BO-ff) and Münster (2020-676 f-S), Germany. All participants are required to provide written informed consent. Findings will be disseminated through peer-reviewed publications, scientific conferences and involvement of relevant stakeholders, patients and the lay public. TRIAL REGISTRATION NUMBER: DRKS00026646.