Assessing the validity of diagnostic criteria, predictors, and consequences of receiving a diagnostic label for functional disorders (FD)

In the general population, 80% of people experience one or more somatic symptoms such as pain, fatigue, diarrhoea in any given month(1). The symptoms are wide ranging and can be classified under many medical specialties from neurological to sensory to digestive. Some of these symptoms can be attributed to a biomedical disease, however, many cannot. It is these symptoms that cannot be explained by biomedical pathology that we call “functional somatic symptoms”. Some of these symptoms can persist and clusters of these symptoms can be classified under the term “Functional Disorders (FD)”(2). Many Functional disorders exists, the most common ones are Fibromyalgia, Chronic Fatigue Syndrome (CFS) and Irritable Bowel Syndrome (IBS).
These disorders represent substantial burden for patients and lead to poorer quality of life, increased sick leave from work and disability(3). In addition, repeated investigations to confirm a diagnosis and treatments can result in high costs to healthcare systems. Therefore, it is important to have a valid and reliable diagnostic criterion to recognise patients’ conditions and refer them to suitable treatment as soon as possible.

Publication 1

Diagnostic labels are usually given by healthcare professionals to identify and categorize groups of patients. These labels can have a major impact on the lives of patients who receive them(4). Having a diagnostic label allows patients to develop a sense of identity by validating their experiences, which can also lead to support and understanding from their surrounding social environment(5). Conversely, diagnostic labels may carry negative impacts for patients. Previous research has linked receiving diagnostic labels to patients experiencing stigma(6, 7) and discrimination(8). 
Considering the impact of receiving a diagnostic label, it is important to comprehensively study the predicting factors of receiving these labels and to systematically analyze their impact on patient lives.

Publication 2a and 2b
This is an important research field because currently diagnostic practices vary between countries and scientific fields and different concepts of functional somatic disorder have important consequences for patients because it determines their future in the medical system – particularly regarding treatment. However, despite recent revisions, the current classifications remain complex and there is variation on how the various concepts are implemented in research and clinic. To address these limitations, an international research group in this area (EURONET-SOMA) proposed a new classification of Functional Somatic Disorder (FSD) (Burton et al. 2020). This classification aims to give an overview of how current criteria work together and to give a more accurate picture of patient experience. However, this concept need to be clarified and tested to ensure we are using the most accurate, reliable and valid criteria to assess and categorise patients with functional somatic symptoms. Publications 2a and 2b will focus on empirically testing a new diagnostic proposal in large-scale population-based samples with follow-up assessments such as Lifelines.