Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a disabling chronic illness. People with ME/CFS experience profound fatigue that does not go away with rest, as well as problems with sleep and memory or concentration. The hallmark symptom is post-exertional malaise (PEM), a worsening of the illness that can start immediately or up to days after even minor physical or mental activity. This "crash" can last hours, days or several months. Further common symptoms include orthostatic intolerance—dizziness or faintness when upright—and pain.
The cause of the disease is unknown. ME/CFS often starts after an infection, such as infectious mononucleosis. Studies find impairment in the nervous and immune systems, as well as in energy production. A diagnosis is established with the presence of clinical symptoms and systematic differential diagnosis, as there is no verified diagnostic laboratory test or imaging procedure available.
ME/CFS symptoms can improve or worsen over time, but a full recovery is uncommon. No therapies or medications are approved to treat the cause of the condition, and treatment or management is aimed at relieving symptoms. Pacing of activities can help avoid PEM which can worsen symptoms for extended periods, and counselling may help in coping with the illness. Before the COVID-19 pandemic, ME/CFS affected two to nine out of every 1,000 people, depending on the diagnostic criteria. Since the pandemic began, with the similarity of long COVID, many more people fit a diagnosis of ME/CFS. It occurs more often in women than in men and is more common in middle age, but can occur at all ages, including childhood.
The societal and economic impact of the disease is large, and the symptoms can be socially isolating. About a quarter of those affected are unable to leave their bed or home. People with ME/CFS often face stigma in healthcare settings, and care is complicated by controversies around the cause and treatments of the illness. Doctors may be unfamiliar with diagnosing the illness, as it is often not fully covered in medical school. Historically, research funding for ME/CFS has been far below that of diseases with comparable impact.
Classification and terminology ME/CFS has been classified as a neurological disease by the World Health Organization (WHO) since 1969, initially under the name benign myalgic encephalomyelitis. The classification as a neurological disease is based on symptoms that indicate a central role of the nervous system. Alternatively, on the basis of abnormalities in immune cells, ME/CFS is labelled a neuroimmune condition. The disease can further be regarded as a post-acute infection syndrome (PAIS) or an infection-associated chronic condition. PAISes such as long COVID and post-treatment Lyme disease syndrome share many symptoms with ME/CFS and are suspected to have a similar cause.
Many names for the illness have been proposed. The most commonly used are myalgic encephalomyelitis, chronic fatigue syndrome, and the combined umbrella term myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Agreement on a name has been difficult because the cause and pathology remain unknown. In the WHO's recent classification, the ICD-11, chronic fatigue syndrome and myalgic encephalomyelitis are named under post-viral fatigue syndrome. The term post-infectious fatigue syndrome was initially proposed as a subset of "chronic fatigue syndrome" with a documented triggering infection, but is also used as a synonym of ME/CFS, or for a broader set of fatigue conditions after infection.
Most individuals with ME/CFS object to the name "chronic fatigue syndrome", which was formalised in 1988. They consider the term simplistic, and that it trivialises the debilitating symptoms, preventing the illness from being taken seriously. There are also issues with the previous term used since 1956, "myalgic encephalomyelitis", as there is limited evidence of brain inflammation (myalgia means 'muscle pain' and encephalomyelitis means 'brain and spinal cord inflammation'). The umbrella term ME/CFS retains the often used phrase CFS without trivialising the disease, but some object to this name too, because they believe previous dissimilar diagnostic criteria for ME and CFS identify separate illnesses.
A 2015 report from the US Institute of Medicine recommended the illness be renamed systemic exertion intolerance disease (SEID) and suggested new diagnostic criteria. While the new name was not widely used, the diagnostic criteria were adopted by the Centers for Disease Control and Prevention (CDC). Like CFS, the name SEID only focuses on a single symptom, and opinion from those affected was generally negative.
Signs and symptoms ME/CFS causes debilitating fatigue, sleep problems, and post-exertional malaise (PEM, overall symptoms getting worse after mild activity). In addition, cognitive issues, orthostatic intolerance (dizziness or nausea when upright) or other physical symptoms may be present (see also ). Symptoms significantly reduce the ability to function and typically last for three to six months before a diagnosis can be confirmed. ME/CFS usually starts after an infection. Onset can be sudden or more gradual over weeks to months.
Core symptoms People with ME/CFS experience persistent debilitating fatigue. It is made worse by normal physical, mental, emotional, and social activity, and is not a result of ongoing overexertion. Rest provides limited relief from fatigue. Particularly in the initial period of illness, this fatigue is described as "flu-like". Individuals may feel "physically drained" and unable to start or finish activities. They may also feel restless while fatigued, describing their experience as "wired but tired". When starting an activity, muscle strength may drop rapidly, which can lead to difficulty with coordination, clumsiness or sudden weakness. Mental fatigue may also make cognitive efforts difficult. The fatigue experienced in ME/CFS is of a longer duration and greater severity than in other conditions characterised by fatigue. The hallmark feature of ME/CFS is a worsening of symptoms after exertion, known as post-exertional malaise or post-exertional symptom exacerbation. PEM involves increased fatigue and is disabling. It can also include flu-like symptoms, pain, cognitive difficulties, gastrointestinal issues, nausea, and sleep problems. All types of activities that require energy, whether physical, cognitive, social, or emotional, can trigger PEM. Examples include attending a school event, food shopping, or even taking a shower. For some, just being in a stimulating environment can be a sufficient trigger. PEM usually starts 12 to 48 hours after the activity, but can also follow immediately after. PEM can last hours, days, weeks, or months. Extended periods of PEM, commonly referred to as "crashes" or "flare-ups" by people with the illness, can lead to a prolonged relapse.
Unrefreshing sleep is a further core symptom. People wake up exhausted and stiff rather than restored after a night's sleep. This can be caused by a pattern of sleeping during the day and being awake at night, shallow sleep, or broken sleep. However, even a full night's sleep is typically non-restorative. Some individuals experience insomnia, hypersomnia (excessive sleepiness), or vivid nightmares.
Cognitive dysfunction in ME/CFS can be as disabling as physical symptoms, leading to difficulties at work or school, as well as in social interactions. People with ME/CFS sometimes describe it as "brain fog", and report a slowdown in information processing. Individuals may have difficulty speaking, struggling to find words and names. They may have trouble concentrating or multitasking, or may have difficulties with short-term memory. Tests often show problems with short-term visual memory, reaction time and reading speed. There may also be problems with attention and verbal memory.
People with ME/CFS often experience orthostatic intolerance, symptoms that start or worsen with standing or sitting. Symptoms, which include nausea, lightheadedness, and cognitive impairment, often improve again after lying down. Weakness and vision changes may also be triggered by the upright posture. Some have postural orthostatic tachycardia syndrome (POTS), an excessive increase in heart rate after standing up, which can result in fainting. Additionally, individuals may experience orthostatic hypotension, a drop in blood pressure after standing.
Other common symptoms Pain and hyperalgesia (an abnormally increased sensitivity to pain) are common in ME/CFS. The pain is not accompanied by swelling or redness. The pain can be present in muscles (myalgia) and joints. Individuals with ME/CFS may have chronic pain behind the eyes and in the neck, as well as neuropathic pain (related to disorders of the nervous system). Headaches and migraines that were not present before the illness can occur as well. However, chronic daily headaches may indicate an alternative diagnosis.
Additional common symptoms include irritable bowel syndrome or other problems with digestion, chills and night sweats, shortness of breath or an irregular heartbeat. Some experience sore lymph nodes and a sore throat. People may also develop allergies or become sensitive to foods, lights, noise, smells or chemicals.
Illness severity ME/CFS often leads to serious disability, but the degree varies considerably. The illness severity is generally classified into four categories: People with mild ME/CFS can usually still work and care for themselves, but they will need their free time to recover from these activities rather than engage in social and leisure activities. Moderate severity impedes activities of daily living (self-care activities, such as making a meal). People are usually unable to work and require frequent rest. Those with severe ME/CFS are homebound and can do only limited activities of daily living, for instance brushing their teeth. They may be wheelchair-dependent and spend the majority of their time in bed. With very severe ME/CFS, people are mostly bed-bound and cannot care for themselves.
Roughly a quarter of those living with ME/CFS fall into the mild category, and half fall into the moderate or moderate-to-severe categories. The final quarter falls into the severe or very severe category. Severity may change over time. Symptoms might get worse, improve, or the illness may go into remission for a period of time. People who feel better for a period of time may overextend their activities, triggering PEM and a worsening of symptoms.
Those with severe and very severe illness experience more extreme and diverse symptoms. They may face severe weakness and greatly limited ability to move. They can lose the ability to speak, swallow, or communicate completely due to cognitive issues. They can further experience severe pain and hypersensitivities to touch, light, sound, and smells. Minor day-to-day activities can be sufficient to trigger PEM.
Individuals with ME/CFS have decreased quality of life when evaluated by the SF-36 questionnaire, especially in the domains of physical and social functioning, general health, and vitality. However, their emotional functioning and mental health are not much lower than those of healthy individuals. Functional impairment in those affected can be greater than multiple sclerosis, heart disease, or lung cancer. Fewer than half of people with ME/CFS are employed, and roughly one in five have a full-time job.
Causes