Fibromyalgia (FM or FMS) is characterized by chronic widespread pain and allodynia (a heightened and painful response to pressure). Its exact cause is unknown but is believed to involve psychological, genetic, neurobiological and environmental factors. Fibromyalgia symptoms are not restricted to pain, leading to the use of the alternative term fibromyalgia syndrome for the condition. Other symptoms include debilitating fatigue, sleep disturbance, and joint stiffness. Some patients also report difficulty with swallowing, bowel and bladder abnormalities, numbness and tingling, and cognitive dysfunction. Fibromyalgia is frequently comorbid with psychiatric conditions such as depression and anxiety and stress-related disorders such as posttraumatic stress disorder. Not all fibromyalgia patients experience all associated symptoms
The cause of fibromyalgia is unknown. However, several hypotheses have been developed including "central sensitization". This theory proposes that fibromyalgia patients have a lower threshold for pain because of increased reactivity of pain-sensitive nerve cells in the spinal cord or brain. Neuropathic pain and major depressive disorder often co-occur with fibromyalgia – the reason for this comorbidity appears to be due to shared genetic abnormalities, which leads to impairments in monoaminergic, glutamatergic, neurotrophic, opioid and proinflammatory cytokine signaling. In these vulnerable individuals psychological stress or illness can cause abnormalities in inflammatory and stress pathways which regulate mood and pain. Eventually a sensitization and kindling effect occurs in certain neurones leading to the establishment of fibromyalgia and sometimes a mood disorder. The evidence suggests that the pain in fibromyalgia results primarily from pain processing pathways functioning abnormally. In simple terms it can be described as the volume of the neurones being set too high and this hyper-excitability of pain processing pathways and under-activity of inhibitory pain pathways in the brain results in the affected individual experiencing pain. Some of the neurochemical abnormalities that occur in fibromyalgia also regulate mood, sleep and energy, thus explaining why mood, sleep and fatigue problems are commonly co-morbid with fibromyalgia
Exercise improves fitness and sleep and may reduce pain and fatigue in some people with fibromyalgia. In particular, there is strong evidence that cardiovascular exercise is effective for some patients.