A brief discussion of diagnostic criteria

The clinical features of ME were first clearly described by the late Dr. Melvin Ramsay MA MD (a physician at the Royal Free Hospital in London during an epidemic outbreak in 1955, and The ME Association's first President). Since then, in the light of there being no diagnostic tests, there have been several more attempts to define the illness by way of its symptoms, although never with all-round agreement.

In recent years there have been the American Center for Disease Control (CDC) definition, the "Oxford Criteria" and more recently the "Canadian Guidelines". Although the first two criteria tend to be used as a diagnostic aid by many clinicians, they were compiled primarily for researchers to identify particular sets of people for their studies. These earlier definitions (of "CFS" as opposed to "ME") give various physical and neurological symptoms; however, in these definitions, the cardinal features of "ME" - the muscle fatigability and pain, and post-exertional malaise - do not have to be present for such a diagnosis. This suggests that nowadays, not everyone with a diagnosis of "Chronic Fatigue Syndrome" necessarily has the disease "ME" as described by Dr Ramsay. It also seems that CFS can cover a spectrum of fatigue-prominent diseases, possibly including illness based in depression, stress or 'burn-out'. However the Canadian Guidelines were developed with clinicians more in mind.

Two other features of ME are first the fluctuation of symptoms from day to day, or within the day; and secondly the tendency for the condition to persist for several years.

Dr Ramsay's description included the following:

The onset of the disease may be sudden and without apparent cause... but usually there is a history of infection of the upper respiratory tract or, occasionally, the gastrointestinal tract with nausea and/or vomiting. Instead of an uneventful recovery, the patient is dogged by persistent and profound fatigue accompanied by a medley of symptoms such as headache, giddiness, muscle pain, cramps or twitchings, muscle tenderness and weakness, paraesthesiae, frequency of micturition, blurred vision and/or diplopia, hyperacusis, tinnitus and a general feeling of 'feeling awful'... the phenomenon of muscle fatigability is the dominant and most persistent feature of the disease and in my opinion a diagnosis should never be made without it. ...If muscle power is found to be satisfactory, a re-examination should be made after exercise; a walk of half a mile is sufficient, as very few ME cases can manage more... Restoration of muscle power can take three to five days or even longer.

From Post-viral Fatigue Syndrome by A. Melvin Ramsay MA MD.

The CDC criteria are broadly as follows:

• Clinically evaluated, unexplained persistent or relapsing chronic fatigue that is of new or definite onset (i.e., not lifelong), is not the result of ongoing exertion, is not substantially alleviated by rest, and results in substantial reduction in previous levels of occupational, educational, social, or personal activities.
• The concurrent occurrence of four or more of the following symptoms: substantial impairment in short-term memory or concentration; sore throat; tender lymph nodes; muscle pain; multi-joint pain without swelling or redness; headaches of a new type, pattern, or severity; unrefreshing sleep; and post-exertional malaise lasting more than 24 hours. These symptoms must have persisted or recurred during 6 or more consecutive months of illness and must not have predated the fatigue.

(Note that although post-exertional malaise is listed, it does not have to be present for this diagnosis to be given.)

The CDC's own website gives further details of the CDC definition.

The Oxford criteria identify two broad syndromes (remember these definitions are primarily for research purposes):

1. Chronic Fatigue Syndrome

• fatigue is the principal symptom: it is severe, disabling and affects physical and mental functioning; it should have been present for a minimum of 6 months during which it was present for more than 50% of the time.
• other symptoms may be present: particularly myalgia, mood swings and sleep disturbances.
• definite onset of symptoms, not life-long.
• exceptions: patients with established medical conditions known to produce chronic fatigue; also patients with a current diagnosis of schizophrenia, manic depressive illness, substance abuse, eating disorder or proven organic brain disease.

2. Post-infectious Fatigue Syndrome (PIFS)

• A sub-type of CFS which either follows an infection or is associated with a current infection (although whether such associated infection is of aetiological significance (i.e. whether it is the cause of the symptoms) is a topic for research).
• To meet the research criteria for PIFS patients must:

i. fulfil the criteria for CFS as defined above (i.e. the Oxford definition)

ii. should also fulfil the following additional criteria:

(a) There is definite evidence of infection at onset or presentation (a patient's self-report is unlikely to be sufficiently reliable).

(b) the syndrome is present for a minimum of 6 months after onset of infection.

(c) the infection has been corroborated by laboratory evidence.

The Canadian guidelines

The new Canadian Clinical Case Definition was written by U.S. and Canadian ME/CFS researchers.

In contrast to the 1994 CDC criteria, which make "fatigue" a compulsory symptom but downplay and make optional post-exertional sickness and other cardinal symptoms, the Canadian clinical case definition specifically selects patients whose condition gets worse with exercise. The clinical definition makes it clear that in order to meet the diagnostic criteria, the patient must become symptomatically ill after exercise, and must also have neurological, neurocognitive, neuroendocrine, dysautonomic (for example, orthostatic intolerance), and immune manifestations. So symptoms other than fatigue, must be present for a patient to meet the diagnostic criteria.

This case definition helps to distinguish ME/CFS patients from chronic fatigue patients, depressed patients, somatization, fibromyalgia, and other diseases with which ME/CFS has been confused, including those that improve with exercise. The Canadian definition specifically states that patients "become worse after exercise rather than better." The new case definition, much of which is backed by research and hard science, is a strong counterstatement to the view held by many psychologists and psychiatrists.