Common functional pain syndromes

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### Key points When a patient presents with pain of no obvious organic origin, they are often labelled as having ‘functional’ pain. The exact diagnosis is derived from the organ system displaying the predominant symptoms e.g. musculoskeletal pain in fibromyalgia (FM) or visceral pain in irritable bowel syndrome (IBS). The worldwide prevalence of all functional pain syndromes (FPS) is 15–20%. World Health Organization (WHO) surveys reveal that ∼10% of primary care patients develop a chronic pain condition within 12 months of initial registration. Of these, at least 50% continue to have symptoms beyond 1 yr. FPS cause enormous economic burden on society with concurrent ramifications for the individual's family in particular and society in general. FM alone has been estimated to cost around £4000 per patient per year. There has been a paradigm shift in the understanding of FPS. The old model of multiple discrete chronic pain conditions is being replaced by a more overarching, although no less complex, state of central sensitivity syndrome (CSS). Evidence is being accrued that FPS represent the phenotypic output of a complex interplay between genetic susceptibility, gene–environment interactions, and environmental triggers. Four common FPS will be reviewed in this article: FM, IBS, temporomandibular dysfunction (TMD), and chronic cardiac chest pain (CCCP). The pathophysiology and management of each will be examined and the case presented for a shared underlying mechanism called CSS. Once this new mechanism is adopted more widely, it will allow for future novel management options to be …