Myalgic encephalomyelitis

Myalgic encephalomyelitis (ME) is a chronic, inflammatory, physically and neurological and immune-mediated disease that presents with symptoms involving multiple bodily systems. It is frequently triggered by a viral infection or a flu-like illness. ME presents with symptoms in the central nervous system (CNS), autonomic nervous system (ANS), immune system, cardiovascular system, endocrine system, digestive system, and musculoskeletal system.

Myalgic encephalomyelitis was first classified as a neurological disease by the World Health Organization (WHO) in 1969, with the publication of the ICD-8 manual.

ME has occurred in both epidemic and sporadic forms.

The hallmark symptom of myalglc encephalomyelitis is post-exertional malaise (PEM), which is the result of intolerance to previously achievable cognitive or physical exertion. Other key symptoms include muscle weakness and easy muscle fatigability, sleep disturbance, and cognitive dysfunction. ANS dysfunction is frequent, although specific symptoms vary from patient to patient and may include postural orthostatic tachycardia (POTS), reduced heart rate variability at night, and both cold and heat intolerance. Other common symptoms include myalgia (muscle pain), neuralgia (neuropathic pain), neck and spine stiffness, and sensory symptoms including sensitivity to light, sound, touch, paraesthesia (skin tingling or numbness) and hyperaesthesia (skin sensitivity and pain, and allodynia). There is a progressive form of ME, but it is rarer than the relapsing-remitting type.

Among adults, ME is more common in women than men. New onset has been observed in children and in adults usually between the ages of 40-60. Bakken et. al notes two age peaks for CFS/ME; age group 10 to 19 years and a second peak in the age group 30 to 39 years.

There are no approved pharmacological treatments for ME anywhere in the world except in Argentina, which has approved the immunomodulator Ampligen for severe ME/CFS as of August 23, 2016.



History
Myalgic encephalomyelitis was first classified as a neurological disease by the World Health Organization in 1969, with the publication of the ICD-8 manual. The ICD-8 did not include any alternative names for myalgic encephalomyelitis although postinfectious encephalomyelitis and all other encephalomyelitis diseases were classified under the same code; fatigue-related alternative names were not added in any later revisions. The alternative name chronic fatigue syndrome (CFS) was not in use at this time; it was proposed in 1987 by the Centers for Disease Control, which adopted new diagnostic criteria the following year.

In the ICD-9, which was published in 1989, the entry for myalglc encephalomyelitis is uses code 323.9:

ME has occurred in both epidemic and sporadic form since at least the 1930s, although it has likely been occurring much longer but was not formally named. The first recorded outbreak of epidemic myalgic encephalomyelitis was in 1934 in Los Angeles and was thought to be an outbreak of atypical polio. After the outbreak in Akureyri, Iceland in 1946, the disease came to be called 'Akureyri Disease' or Icelandic disease through much of the 1940s and 1950s. It was named ME after London's Royal Free Hospital outbreak in 1955. Other names included benign myalgic encephalomyelitis and epidemic neuromyasthenia.

After the Incline Village outbreak in Nevada in 1984, the disease came to be called and redefined as chronic fatigue syndrome (CFS). The most recent putative outbreak was in Arizona in 1996.

Disease name

 * Myalgic - of or relating to myalgia (muscle pain).


 * Encephalo: Refers to the brain.


 * -myel: relating to the spinal cord.

The name myalgic encephalomyelitis was first used in 1956 in an article in the Lancet medical journal to describ findings from the 1955 Royal Free Hospital outbreak in London, UK. The term myalgic encephalomyelitis is a portmanteau of several of the key signs and symptoms of the disease: myalgic (muscle pain), encephalo (brain), myel (spinal cord), itis (inflammation). The central nervous system (brain and spinal cord) are inflamed.
 * -itis: Inflammation.

Benign myalgic encephalomyelitis
Benign myalgic encephalomyelitis was the term used by the World Health Organization from 1969, with the prefix "benign" used to denote that M.E. was not fatal, the prefix benign was later dropped since M.E. can cause death, for example the deaths of Merryn Crofts and Sophia Mirza. Merryn Crofts had very severe ME, was bedbound and unable to eat. She weighed six stone (84 lbs) at her death; her autopsy revealed inflammation of the dorsal root ganglia. Merryn's death certificate was the second in the UK to attribute a death to ME.

Disease of a thousand names
Myalgic Encephalomyelitis has been referred to as the "disease of a thousand names". Other names used or proposed in the history of the myalgic encephalomyelitis include atypical polio, Icelandic disease, benign ME, epidemic neuromyasthenia, chronic fatigue syndrome, Chronic Fatigue Immune Dysfunction Syndrome (CFIDS), and systemic exertion intolerance disease (SEID). This has lead to much confusion as a variety of names have been used at different times to describe discrete outbreaks as well as a larger and potentially more heterogenous population of sporadic cases, defined by a wide variety of diagnostic criteria. Some names have emphasized particular symptoms or pathology, including chronic fatigue syndrome and myalgic encephalomyelitis.

A survey by The MEAction Network in 2016 found that the majority of patients prefer the name ME to other names including chronic fatigue syndrome.

Myalgic encephalomyelitis (ME) was the original name for chronic fatigue syndrome (CFS); the names are used interchangeably or with the acronym ME/CFS.

Onset
According to Dr Byron Hyde, after an incubation period of 4 to 7 days, the prodromal phase generally involve a flu-like illness with low-grade fever. In the majority but not all cases, an infection or infectious process is evident. Two to seven days later, a chronic phase commences, characterized by a measurable diffuse change in the function of the CNS. It is this second phase, persistent phase that most characterizes ME.

Signs and symptoms
Myalgic encephalomyelitis is a neurological disease that affects multiple bodily systems, causing a widespread combination of symptoms. Symptoms can range from mild to very severe and can include:


 * ataxia (coordination difficulties)
 * cognitive dysfunction
 * fatigability
 * gastrointestinal symptoms
 * headache
 * low-grade fever, temperature instability
 * muscle weakness and fatiguability
 * myalgia (muscle pain)
 * neck and back or spinal cord stiffness
 * neuralgia (nerve pain)
 * othostatic intolerance
 * post-exertional malaise
 * sensitivity to heat or cold
 * sensitivity to light, sound and/or touch
 * sleep dysfunction

Symptom presentation and severity can vary considerably day to day and even hour to hour. Overexertion can exacerbate all symptoms, and post-exertional malaise often delayed by 24 hours or more. The US National Institutes of Health (NIH) notes that sensitivity to noise, light and chemicals may force patients to withdraw from society.

Post-exertional malaise
A core symptom, post-exertional malaise (PEM), is intolerance to previously trivial mental or physical effort such as attending a child's school event, running an errand or grocery shopping, taking a shower or brushing teeth; this causes a worsening of symptoms, and deterioration of health from persistent or repeated exertion. The severity of a patient's symptoms often depends on the time period since the disease was contacted and rate of progression of each patient. The rate of progression can be accelerated by physical or cognitive activity beyond a patient's limits over long periods, which typically entails anaerobic activity.

Clinical findings
Although there is no definitive biomarker, several signs and findings have been frequently observed in clinical settings:
 * high antibody titers to specific infections (including EBV, HHV-6, and Coxsackie B among others)
 * Hormone imbalance
 * immunological abnormalities
 * low natural killer cell function
 * low red blood cell magnesium
 * postural orthostatic tachychardia (POTS)
 * physical and mental exertion, sensory input cause relapse (PEM)

Diagnosis


There are several proposed criteria for diagnosing ME including the International Consensus Criteria (ICC) and the Canadian Consensus Criteria (CCC). The original criteria developed by Melvin Ramsay, the Ramsay definition, is not used for diagnosing ME today.

Generally accepted criteria for diagnosing ME/CFS and ME

 * Canadian Consensus Criteria (CCC) A diagnosis of moderate and severe forms of ME/CFS are accurately made using this criterion. Adults can be diagnosed at 6 months while pediatric cases are diagnosed at three months.
 * International Consensus Criteria (ICC)  This criteria will accurately diagnose myalgic encephalomyelitis (ME). There is no requirement that the individual have symptoms for a specified period of time for diagnosis, as opposed to CCC, Fukuda, and SEID, which all require 6 months in adults.
 * Systemic Exertion Intolerance Disease (SEID)

ME/CFS (SEID) is accurately diagnosed when the core symptoms are met. The Institute of Medicine report is a whole is a comprehensive review of the medical literature available at time of publication (2015). Adults can be diagnosed at 6 months while pediatric cases are diagnosed at three months.

Other diagnostic criteria
Several, overly broad criteria have been proposed and are in use. These criteria likely capture some patients with the disease characterized in the medical literature on epidemic ME, exclude others, and also include patients with a wide range of other undiagnosed conditions including cancer, depression, and a range of autoimmune diseases. The United Kingdom's Oxford criteria for chronic fatigue syndrome is the broadest and likely least discerning definition. (The US Institute of Medicine report called for its complete retirement.) The US Centers for Disease Control's (CDC) Fukuda criteria, in use since 1994, is also overly broad. The Institute of Medicine report developed the criteria of Systemic Exertion Intolerance Disease (SEID) and although it can diagnose ME patients with the minimum core symptoms, it does not describe the array of symptoms those suffering with ME experience. Symptoms such as neurological, immune/gastrointestinal/genitourinary impairment, and energy metabolism/ion transport impairment; these symptoms are necessary for a diagnosis under the ICC. The CCC requires neurological, autonomic, neuroendocrine, immune system, and myalgia symptoms to meet its ME/CFS diagnostic criteria.

Differential diagnosis
The signs and symptoms of ME can be similar to other medical problems, "such as cancer, multiple sclerosis, lupus, brucellosis, or another condition." Additional testing may be needed to help distinguish ME from these other problems.

Pathophysiology


ME is a multi-system disease. Numerous biological abnormalities have been found in multiple bodily system, however no common, central cause or mechanism has yet been elucidated.

Sex differences


A Norwegian CFS/ME study shows that the disease affects all ages, with two peak ages of 10-19 years and 30-39 years; it is more common in women than in men. Research by the Open Medicine Foundation cited in its paper, Metabolic features of chronic fatigue syndrome which studied severe CFS, found that the disease is different in men and women but this is not related to testosterone or estrogen. Michael VanElzakker notes there are male and female differences in neuropathic pain. A study of UK and Dutch cohorts found "younger children had a more equal gender balance compared to adolescents and adults."

Genetic risks
Myalgic encephalomyelitis and chronic fatigue syndrome have been reported to run in families, although ME and CFS are not considered inherited illnesses, there is evidence of a genetic predisposition.

Potential causes
Although risk factors for myalgic encephalomyelitis have been identified, no single definitive virus has been found in all cases, which has led to the claim that ME is a common end path of a variety of infectious insults. It is still possible ME involves some combination of both environmental and genetic factors. Various theories try to combine the known data into plausible explanations. Several theories suggest that ME is an inappropriate immune response to an infection, a theory bolstered by the observation that there is sometimes a family history of autoimmune disease. There is also a shift from the Th1 type of helper T cells, which fight infection, to the Th2 type, which are more active in allergy and more likely to attack the body.



Viruses
Other theories describe ME as an immune response to a chronic infection. The association between ME and the Coxsackie B, HHV-6, and HHV-7 viruses  suggests a potential viral contribution in at least some individuals. Evidence from epidemic myalgic encephalomyelitis strongly point to an enterovirus, however, in most outbreaks, no virus was successfully isolated.

Bacteria
Others believe ME may sometimes result from a chronic infection with spirochetal bacteria, such as lyme disease. Another bacterium that has been implicated in ME is chlamydia pneumoniae. Protein findings relating to several infections have seen found in the oligoclonal bands ME of patients.

The vagus nerve infection hypothesis (VNIH) accounts for why so many different infectious onsets could be responsible. The vagus nerve runs from the brain stem and throughout the body and has an impact on many body systems.

Given the uncertainty regarding the cause, ME and CFS patients are barred from donating blood or organs in the United Kingdom, United States and New Zealand while symptoms persist.

Treatments


There is no cure for ME and no country has approved any pharmacological treatment for the disease except, Argentina which has approved Ampligen for the treatment of severe ME/CFS. However the effectiveness of Ampligen is under dispute. Other medications have been used off-label for ME with varying effectiveness in some patients.

Treatments for sleep problems, headaches, pain or other symptoms are utilized by some doctors for some patients although these are treating symptoms and not ME itself.

Success of treating symptoms of ME is not well researched or documented.

An immune system modulator drug called Rituximab has failed in a phase III clinical trial. The antiviral Valganciclovir failed in a controlled nine month study against ME patients positive for Herpes Simplex 6 and Epstein Barr viral infections.

Epidemiology
ME has been found world-wide, in at least 75 epidemics documented in published papers from the 1930s to the 1980s. Epidemics often occur in enclosed communities such as schools and hospitals.

As observed in many autoimmune disorders, ME is more common in females than males; the mean sex ratio is approximately 2-3 females for every male. In children the sex ratio is approximately equal.

Co-morbidities


Clinicians have observed several predisposing conditions, co-morbidities, overlapping conditions, and increased risks for secondary diseases in patients with ME. However, as no large-scale epidemiological studies, genetic studies, or family studies have been done, there is little that can be said definitively about the rate or underlying biological reasons for these potentially related conditions. Overlapping diagnostic criteria and the lack of a biomarker in many of these conditions add to the confusion and diagnostic uncertainty. Moreover, certain conditions such as postural orthostatic tachycardia syndrome (POTS) and neurally mediated hypotension (NMH) and idiopathic intracranial hypertension (IIH/IH) and fibromyalgia (FM/FMS) can occur in or be co-morbid with numerous conditions, including ME.

The following are some syndromes and diseases that have been associated with or misdiagnosed as ME:
 * fibromyalgia
 * Lyme disease and chronic Lyme disease
 * idiopathic intracranial hypertension
 * postural orthostatic tachychardia syndrome
 * irritable bowel syndrome
 * thyroid disease
 * Ehlers-Danlos syndrome
 * Sjögren's syndrome
 * multiple chemical sensitivity

A Swedish study of 234 ME/CFS patients meeting the Canadian Consensus Criteria found that 13.2% had tonsillar herniations severe enough to be considered a Chiari Malformation. 49% had hypermobility and 20% met criteria for hEDS (Ehlers-Danlos syndrome with hypermobility), while 96% had fibromyalgia trigger point pain, with 67% meeting the diagnostic criteria for fibromyalgia.

Notable studies
Due to lack of funding by governments around the world there has been little biological research into ME/CFS. There are studies which do reveal neurological involvement, metabolic features, and other abnormalities.
 * 2014, Brains of People With Chronic Fatigue Syndrome Offer Clues About Disorder
 * 2016, Metabolic features of chronic fatigue syndrome
 * 2016, CDC Multi-site Clinical Assessment of CFS
 * 2019, Evidence of widespread metabolite abnormalities in Myalgic encephalomyelitis/chronic fatigue syndrome: assessment with whole-brain magnetic resonance spectroscopy
 * List of abnormal findings in chronic fatigue syndrome and myalgic encephalomyelitis