DEFINITION OF ME
Whereas CFS is based on a single symptom, defined as medically unexplained fatigue which has been present for at least six months (accompanied by recurrent sore throat and tender lymph glands, together with cognitive impairment), the cardinal features of ME are quite different.
Understanding of ME has been hampered by a lack of agreement on diagnostic criteria, yet there have been several attempts to characterise the illness, each accordingly closely with the others, all based on epidemiological observations.
Two classic definitions have been put forward:
The Wallis descriptive working definition
In 1955, A.L.Wallis devised the first working definition, albeit from observations of patients during one apparent outbreak in Cumberland, England, in 1955. The elements of this definition - applicable to adults (a definition for children was devised separately) -were: A systemic illness with relatively low fever or subnormal temperatures.
- Marked muscle fatigability.
- Mental changes with impairment of memory, changes in mood, sleep disorders and irritability or depression.
- Involvement of the autonomic nervous system resulting in orthostatic tachycardia, coldness of the extremities, episodes of sweating or profound pallor, sluggish pupils, bowel changes and frequency of micturition, possibly as a result of a lesion of the hypothalamus.
- Diffuse and variable involvement of the central nervous system, leading to ataxia, weakness and/or sensory changes in a limb, nerve root or a peripheral nerve.
- Muscular pain, tenderness and myalgia, and
- Recurrence in some patients over a period of several years.
However, the most-quoted definition was outlined by Dr Melvin Ramsay in 1988
Ramsay Definition 1988
In a review of 1988, Ramsay described the adoption of the following diagnostic criteria, based on his epidemiological experience on 700 patients seen in clinic, some 50% of whom had evidence of enteroviral infection, and 2,000 postal questionnaires (including 420 from patients ill for more than 10 years). a) A syndrome initiated by a viral infection commonly described as a respiratory/gastro intestinal illness, though a gradual or more dramatic onset following neurological, cardiac or endocrine disability is recognised. b) The cardinal features, in a patient who has previously been physically and mentally fit, with a good work record are:
Clearly, the illness ME is characterised principally by Generalised or localised muscle fatigue after minimal exertion, relapses, neurological disturbances and variable involvement of cardiac and other bodily systems.
- Generalised or localised muscle fatigue after minimal exertion with prolonged recovery time.
- Neurological disturbance, especially of cognitive, autonomic and sensory functions, often accompanied by marked emotional lability and sleep reversal.
- Variable involvement of cardiac and other bodily systems.
- An extended relapsing course with a tendency to chronicity.
- Marked variability of symptoms both within and between episodes.