Following the use of a modified version of the original London Criteria for ME in the PACE Trial, there have been questions about what the London Criteria is and how it is defined.
Below is the version that appeared in the 1994 Task Force Report on ME, CFS and PVFS, followed by some notes.
Dr Charles Shepherd
Hon Medical Adviser, ME Association
21 February 2011
LONDON CRITERIA FOR M.E.
Authors: Dowsett EG, Goudsmit E, Macintyre A, Shepherd CB.
In: Report from The National Task Force on Chronic Fatigue Syndrome (CFS), Post Viral Fatigue Syndrome (PVFS), Myalgic Encephalomyelitis (ME). Westcare, 1994. pp. 96-98.
All three criteria must be present for a diagnosis of ME/PVFS to be made:
1. Exercise-induced fatigue precipitated by trivially small exertion (physical or mental) relative to the patient's previous exercise tolerance.
2. Impairment of short-term memory and loss of powers of concentration, usually coupled with other neurological and psychological disturbances such as emotional lability (= being upset by things that would not normally cause distress), nominal dysphasia (= difficulty finding the right word), disturbed sleep patterns, dysequilibrium (= imbalance or unsteadiness rather than vertigo/spinning round) or tinnitus (= noises in the ear).
3. Fluctuation of symptoms, usually precipitated by either physical or mental exercise.
These symptoms should have been present for at least 6 months and should be ongoing.
Although ME/PVFS typically follows an infection, usually a viral illness (which may be subclinical) in a previously fit and active person, it has also been observed to be triggered by other factors such as immunisations, life traumas and exposure to chemicals. Furthermore, in a minority of patients, ME/PVFS has a gradual onset with no apparent triggering factor. For these reasons proof of a preceding viral illness is not a prerequisite for diagnosis.
Many symptoms are experienced by people suffering from ME/PVFS and in the right symptomatic context they contribute to the validity of the diagnosis.
Nevertheless, not all people suffering from ME/PVFS experience all these symptoms and their absence does not exclude the condition.
These symptoms can be subdivided into the following two categories:
> bouts of inappropriate night or day-time sweating
> Raynaud's phenomenon (= cold extremities)
> postural hypotension (= lowered blood pressure on standing)
> disturbance of bowel motility manifesting as recurrent diarrhoea or occasionally constipation (these symptoms are frequently indistinguishable from those of irritable bowel syndrome)
> photophobia (= sensitivity to bright light); blurred vision due to disturbed accommodation
> hyperacusis (= sensitivity to loud noise)
> frequency of micturition (= passing urine more often than normal); nocturia (= passing urine at night)
Immunological (symptoms suggesting persistent viral infection):
> episodes of low-grade fever (not exceeding an oral temperature of 38.6C) combined with feeling feverish, (i.e. a down-regulated ‘thermostat')
> sore throat which may be persistent or recurrent (i.e. present for at least one week per month)
> arthralgia (pain but not swelling in the joints) – fixed or migratory
This list is by no means exhaustive.
Headaches, nausea and bloating, for instance are common symptoms in many patients but are not sufficiently discriminative because of their widespread occurrence in many other disorders. The curious intolerance to alcohol and hypersensitivity to drugs are highly specific in this context. It should also be emphasised that the symptoms of ME tend to vary capriciously from hour to hour and day to day. Nevertheless it is absolutely characteristic that they tend to be exacerbated by physical or mental exertion and the association should always be sought whilst taking the history.
• The London Criteria was produced at a time when clinicians, researchers and scientific journals were becoming increasingly reluctant to use the term ME in a research context – preferring the term CFS instead. Consequently, there was very little research into ME taking place. The London Criteria, which were designed for research purposes, are based on Dr Melvin Ramsay's clinical description of ME as can be found on pages 30 – 31 of the second edition of his book Postviral fatigue syndrome – The saga of Royal Free disease (re-published by and available from The ME Association). Dr Ramsay was not involved in the process to develop the London Criteria because he died in 1990.
• The London Criteria was published in 1994 in the Task Force Report and was subsequently made use of in a small number of research studies – the most important one being the research carried out by Costa et al which demonstrated brain stem hypoperfusion. (ref: Costa D et al. Brainstem perfusion is impaired in patients with myalgic encephalomyelitis/chronic fatigue syndrome. Quarterly Journal of Medicine, 1995, 88, 767 – 773. Abstract: http://www.ncbi.nlm.nih.gov/pubmed/8542261
• The London Criteria do not require the presence of pain – because pain is not always present in ME and, while Dr Melvin Ramsay includes the possible presence of muscle twitching and tenderness, his clinical description of ME it does not require pain to be present to make the diagnosis. The emphasis is on exercise-induced muscle fatigue.
• The London Criteria now requires updating to take account of developments in our understanding of the illness since 1993 (when it was prepared) and current requirements for research criteria. Some proposals were recently put forward in a paper: Goudsmit E; Shepherd C; Dancey P, Howes S. ME; Chronic fatigue syndrome or distinct clinical entity. Health Psychology Update, 2009, 18, 26 – 33. Relevant investigations and conditions that should be excluded, as in the various research criteria for CFS, also need to be added.
• The MEA was not involved in the decision to use a modified version of the London Criteria in the PACE trial.
• MEA statement on the PACE trial: https://meassociation.org.uk/?p=4607