Mental disorders in people with undiagnosed diseases presenting to German centres for rare diseases - prevalence, type and relevance.

People presenting to centres for rare diseases (CRD) for diagnostic work-up often suffer from mental disorders. The prevalence and distribution of these mental disorders and their relevance for care remain largely unclear and well-controlled multicentre studies are missing. The ZSE-DUO study was a multicentre, prospective, controlled cohort study involving 11 German CRD. In total, 662 adult patients with an unclear diagnosis were evaluated by an additional mental health specialist along with their usual CRD care. Mental disorders were assessed through a standardized clinical examination, including the Mini-DIPS interview. Prevalence of diagnosed mental disorders (ICD-10 coding) was assessed and compared to population prevalence. A total of 54.5 % (361 patients) of adults with unexplained symptoms presenting to a CRD had current mental disorders. Mental disorders were deemed the sole explanation for the entire symptomatology in 53.5 % of cases. In 36.2 % of cases, a combination of a mental disorder with a somatic disease was considered to explain the unexplained symptoms. In 8.3 % of cases, it was assessed that the mental disorder was not involved in explaining the unexplained symptoms. Assessing whether a mental disorder contributes to the patient's symptom complex is crucial for determining suitable treatment strategies in terms of a bio-psycho-social approach.