Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating long-term medical condition. People with ME/CFS experience delayed worsening of the illness after minor physical or mental activity, which is the hallmark symptom of the illness.[10] Other core symptoms are a greatly reduced ability to do tasks that were previously routine, severe fatigue that does not improve much with rest, and sleep disturbances. Further common symptoms include dizziness or nausea when sitting or standing, along with memory and concentration issues and pain.[3]
The root cause(s) of the disease are unknown.[11] ME/CFS often starts after a flu-like infection, for instance, after mononucleosis.[12] In some people, physical trauma or psychological stress may also act as a trigger.[10]: 10 ME/CFS can run in families, though the genes that contribute to ME/CFS risk are not known.[13] ME/CFS is associated with changes in the nervous and immune systems, energy metabolism, and hormone production.[14] Diagnosis is based on symptoms because no diagnostic test is available.[7]
The severity of the illness can fluctuate over time, but full recovery is uncommon.[12] Treatment is aimed at relieving symptoms, as no therapies or medications are approved to treat the condition.[2]: 29 Pacing one's activities to avoid flare-ups may help manage symptoms, and counselling may aid in coping with the illness.[8] Before the COVID-19 pandemic, ME/CFS affected roughly one in every 150 people, although estimates varied widely.[9] However, many people with long COVID fit ME/CFS diagnostic criteria.[15] ME/CFS occurs more often in women as in men. It most commonly affects adults between ages 40 and 60 but can occur at other ages, including childhood.[16]
ME/CFS has a large social and economic impact. About a quarter of individuals are severely affected and unable to leave their bed or home.[10]: 3 The disease can also be socially isolating.[17] People with ME/CFS often face stigma in healthcare settings and care is complicated by controversies around the cause and potential treaments of the illness.[18] Clinicians may be unfamiliar with ME/CFS, as it is often not covered in medical school.[15] Historical research funding for ME/CFS has been far below that of diseases with comparable impact.[19]
ME/CFS has been classified as a neurological disease by the World Health Organization (WHO) since 1969, initially under the name benign myalgic encephalomyelitis.[20] In the ICD-10, the code for ME/CFS listed only (benign) ME, and there was no mention of CFS; clinicians often used diagnostic codes for fatigue and malaise, or fatigue syndrome, for people with CFS.[21] In the WHO's most recent classification, the ICD-11, both chronic fatigue syndrome and myalgic encephalomyelitis are named in the 8E49 code post-viral fatigue syndrome, classified under other disorders of the nervous system.[22]
The cause of the illness is unknown and the classification is based on symptoms which indicate a central role of the nervous system.[23] Alternatively, based on abnormalities in immune cells, ME/CFS may better fit into a classification of a neuroimmune condition.[24]