Central and peripheral mechanisms of pain in fibromyalgia: scoping review protocol.

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Fibromyalgia is characterised by widespread musculoskeletal pain, which may present with fatigue, depression, anxiety, sleep and cognitive disturbances. It is the second most prevalent rheumatic disease. An accurate diagnosis is challenging, since its symptoms may resemble diverse conditions such as carpal tunnel syndrome, Raynaud syndrome, Sjögren syndrome, amongst others. Neuropathic pain and autonomic dysfunction in fibromyalgia suggest the involvement of the nervous system. Ion channels, neurotransmitters and neuromodulators may play a role. Small fibre neuropathy (SFN) may also cause chronic widespread pain. SFN may occur in 50% of fibromyalgia patients, but its role in the disease is unknown. Despite several efforts to synthesise the evidence on the mechanisms for pain in fibromyalgia, there are few studies applying an integrative perspective of neurochemical, immunological, and neuroanatomical characteristics, and their relevance to the disease. This protocol aims to clarify the mechanisms of the central and peripheral nervous system associated with pain in fibromyalgia. We will retrieve published studies from Web of Science, MEDLINE, Scopus, EBSCOhost, Ovid and Google Scholar. All clinical studies or experimental models of fibromyalgia reporting imaging, neurophysiological, anatomical, structural, neurochemical, or immunological characteristics of the central or peripheral nervous systems associated with pain will be included. Exclusion criteria will eliminate studies evaluating pain without a standardised measure, studies written in languages different from Spanish or English that could not be appropriately translated, and studies whose full-text files could not be retrieved after all efforts made. A narrative synthesis will be performed.