The International Consensus Criteria (ICC-ME), developed in 2011 by an International Consensus Panel consisting of clinicians and researchers, provides the most definitive formalized classification of myalgic encephalomyelitis (ME) symptoms.
These criteria are, incidentally, the only criteria consistent with the neurological classification of ME in the World Health Organization’s International Classification of Diseases (ICD G93.3).
Less specific symptom classifications, with a greater focus on fatigue and biopsychosocial-related illness are provided by the 2003 Canadian Consensus Criteria (CCC) for ME/CFS and by the 1994 Fukuda Definition for CFS.
A comprehensive symptom checklist for CFS, with less specificity, has been developed by Dr Katrina Berne.
ME symptoms in detail
The ICC-ME defines ME as an acquired neurological disease with complex global dysfunctions. Pathological dysregulation of the nervous, immune and endocrine systems, with impaired cellular energy metabolism and ion transport are prominent features.
A patient will meet the criteria for postexertional neuroimmune exhaustion (A), at least one symptom from three neurological impairment categories (B), at least one symptom from three immune/gastro-intestinal/genitourinary impairment categories (C), and at least one symptom from energy metabolism/transport impairments (D).
- Postexertional neuroimmune exhaustion (PENE pen’-e): Compulsory
This cardinal feature is a pathological inability to produce sufficient energy on demand with prominent symptoms primarily in the neuroimmune regions. Characteristics are as follows:
- Marked, rapid physical and/or cognitive fatigability in response to exertion, which may be minimal such as activities of daily living or simple mental tasks, can be debilitating and cause a relapse.
- Postexertional symptom exacerbation:e.g.acute flu-like symptoms, pain and worsening of other symptoms.
- Postexertional exhaustion may occur immediately after activity or be delayed by hours or days.
- Recovery period is prolonged, usually taking 24 h or longer. A relapse can last days, weeks or longer.
- Low threshold of physical and mental fatigability (lack of stamina) results in a substantial reduction in pre-illness activity level.
Operational notes: For a diagnosis of ME, symptom severity must result in a significant reduction of a patient’s premorbid activity level.Mild(an approximate 50% reduction in pre-illness activity level),moderate(mostly housebound),severe(mostly bedridden) or very severe(totally bedridden and need help with basic functions). There may be marked fluctuation of symptom severity and hierarchy from day to day or hour to hour. Consider activity, context and interactive effects.
Recovery time: e.g. Regardless of a patient’s recovery time from reading for ½ hour, it will take much longer to recover from grocery shopping for ½ hour and even longer if repeated the next day – if able. Those who rest before an activity or have adjusted their activity level to their limited energy may have shorter recovery periods than those who do not pace their activities adequately.Impact: e.g. An outstanding athlete could have a 50% reduction in his/her pre-illness activity level and is still more active than a sedentary person.
- Neurological impairments
At least one symptom from three of the following four symptom categories
- Neurocognitive impairments
- Difficulty processing information: slowed thought, impaired concentration e.g. confusion, disorientation, cognitive overload, difficulty with making decisions, slowed speech, acquired or exertional dyslexia
- Short-term memory loss:e.g. difficulty remembering what one wanted to say, what one was saying, retrieving words, recalling information, poor working memory
- Headaches:e.g. chronic, generalized headaches often involve aching of the eyes, behind the eyes or back of the head that may be associated with cervical muscle tension; migraine; tension headaches
- Significant pain can be experienced in muscles, muscle-tendon junctions, joints, abdomen or chest. It is noninflammatory in nature and often migrates. e.g. generalized hyperalgesia, widespread pain (may meet fibromyalgia criteria), myofascial or radiating pain
- Sleep disturbance
- Disturbed sleep patterns:e.g. insomnia, prolonged sleep including naps, sleeping most of the day and being awake most of the night, frequent awakenings, awaking much earlier than before illness onset, vivid dreams/nightmares
- Unrefreshed sleep:e.g. awaken feeling exhausted regardless of duration of sleep, day-time sleepiness
- Neurosensory, perceptual and motor disturbances
- Neurosensory and perceptual:e.g. inability to focus vision, sensitivity to light, noise, vibration, odour, taste and touch; impaired depth perception
- Motor:e.g. muscle weakness, twitching, poor coordination, feeling unsteady on feet, ataxia
Notes: Neurocognitive impairments, reported or observed, become more pronounced with fatigue. Overload phenomena may be evident when two tasks are performed simultaneously. Abnormal accommodation responses of the pupils are common. Sleep disturbances are typically expressed by prolonged sleep, sometimes extreme, in the acute phase and often evolve into marked sleep reversal in the chronic stage. Motor disturbances may not be evident in mild or moderate cases but abnormal tandem gait and positive Romberg test may be observed in severe cases.
- Neurocognitive impairments
- Immune, gastro-intestinal and genitourinary Impairments
At least one symptom from three of the following five symptom categories
- Flu-like symptoms may be recurrent or chronic and typically activate or worsen with exertion.e.g. sore throat, sinusitis, cervical and/or axillary lymph nodes may enlarge or be tender on palpitation
- Susceptibility to viral infections with prolonged recovery periods
- Gastro-intestinal tract:e.g. nausea, abdominal pain, bloating, irritable bowel syndrome
- Genitourinary: e.g. urinary urgency or frequency, nocturia
- Sensitivities to food, medications, odours or chemicals
Notes: Sore throat, tender lymph nodes, and flu-like symptoms obviously are not specific to ME but their activation in reaction to exertion is abnormal. The throat may feel sore, dry and scratchy. Faucial injection and crimson crescents may be seen in the tonsillar fossae, which are an indication of immune activation.
- Energy production/transportation impairments: At least one symptom
- Cardiovascular: e.g. inability to tolerate an upright position – orthostatic intolerance, neurally mediated hypotension, postural orthostatic tachycardia syndrome, palpitations with or without cardiac arrhythmias, light-headedness/dizziness
- Respiratory: e.g. air hunger, laboured breathing, fatigue of chest wall muscles
- Loss of thermostatic stability: e.g. subnormal body temperature, marked diurnal fluctuations; sweating episodes, recurrent feelings of feverishness with or without low grade fever, cold extremities
- Intolerance of extremes of temperature
Notes: Orthostatic intolerance may be delayed by several minutes. Patients who have orthostatic intolerance may exhibit mottling of extremities, extreme pallor or Raynaud’s Phenomenon. In the chronic phase, moons of finger nails may recede.
Symptoms may progress more slowly in children than in teenagers or adults. In addition to postexertional neuroimmune exhaustion, the most prominent symptoms tend to be neurological: headaches, cognitive impairments, and sleep disturbances.
- Headaches: Severe or chronic headaches are often debilitating. Migraine may be accompanied by a rapid drop in temperature, shaking, vomiting, diarrhoea and severe weakness.
- Neurocognitive impairments: Difficulty focusing eyes and reading are common. Children may become dyslexic, which may only be evident when fatigued. Slow processing of information makes it difficult to follow auditory instructions or take notes. All cognitive impairments worsen with physical or mental exertion. Young people will not be able to maintain a full school programme.
- Pain may seem erratic and migrate quickly. Joint hypermobility is common.
Notes: Fluctuation and severity hierarchy of numerous prominent symptoms tend to vary more rapidly and dramatically than in adults.
——— Myalgic encephalomyelitis
——— Atypical myalgic encephalomyelitis: meets criteria for postexertional neuroimmune exhaustion but has a limit of two less than required of the remaining criterial symptoms. Pain or sleep disturbance may be absent in rare cases.
Exclusions: As in all diagnoses, exclusion of alternate explanatory diagnoses is achieved by the patient’s history, physical examination, and laboratory/biomarker testing as indicated. It is possible to have more than one disease but it is important that each one is identified and treated.
Primary psychiatric disorders, somatoform disorder and substance abuse are excluded. Paediatric:‘primary’ school phobia.
Comorbid entities: Fibromyalgia, myofascial pain syndrome, temporomandibular joint syndrome, irritable bowel syndrome, interstitial cystitis, Raynaud’s phenomenon, prolapsed mitral valve, migraines, allergies, multiple chemical sensitivities, Hashimoto’s thyroiditis, Sicca syndrome, reactive depression. Migraine and irritable bowel syndrome may precede ME but then become associated with it. Fibromyalgia overlaps.