Reasons why ME Does Not Belong to the MUS Category…and So Forth

By Norwegian ME Association

Invest in ME have translated this article which was kindly provided by the Norwegian ME Association


From the Journal of IiME Volume 2 Issue 2


1. ME does not belong to the description of Medically Unexplained Symptoms (MUS).

The classic presentation of ME is as an illness with its own diagnosis and diagnostic code, and as such, ME does not fulfill the criteria of the MUS category as “not fitting any known diagnosis”.  Contrast this with an invitation to a seminar in the Health Directorate 26. September 2008. Dr Wyller writes that the diagnosis of Chronic Fatigue Syndrome (CFS) is not in the WHO ICD publication (2008:8). This is incorrect information which has been pointed out earlier. CFS is in the index with a reference to the diagnostic code G93.3. As CFS refers to the same diagnostic code as ME, this means that the condition must be classified under the same code and not under a psychiatric illness (e.g. neurasthenia (chronic fatigue - is not the same as ME/CFS) with code F48.0)(ICD10, printed edition from 1992).

Many therefore refer to the description ME/CFS. See also KITH 2006. The illness and the illness presentation are not new, neither internationally or in Norway. According to infectious disease specialist and previously head of department at Ullevål University Hospital, Oddbjørn Brukbakk, the condition is described in classic, old medical literature in infectious diseases. The diagnosis myalgic encephalopathy/encephalomyelitis (ME)/Post-Viral fatigue syndrome does not belong to the umbrella term MUS for various reasons. This will be examined more closely below.

3.1  2. The WHO classification of ME/Post-Viral Fatigue Syndrome

The World Health Organisation (WHO) was established in 1948. Before 1965 the condition debility and undue fatigue in the international classification system was placed under code 790.1. The condition was not referred to as ME before 1965. So the first time the WHO referred to ME was in 1965 ICD-8. This was first officially published in 1969 9ICD-8: Vol I code 323, page 158; Vol II (Code Index) page 173). ICD-9 was approved in 1977, and ME was listed in the alphabetical index under code 323.9 in Volume II, page 182.

 The World Health Organisation (WHO) approved ME/Post-Viral Fatigue Syndrome as an illness in its own right in 1969 (Marshall, Williams and Hooper, 2001), and the illness was given the following code in the international classification of diseases: ICD-10, 93.3 in the chapter of neurological disorders. According to the taxonomic system of the WHO’s international classification system, it is not allowed to classify an illness in more than one category. The Norwegian healthcare officials have endorsed the classification system, something which legally binds the Norwegian doctors and healthcare officials into following  this system. The system does not allow individual doctors for their own good to classify the condition as F48.0 under mental disorders as long as the criteria for ME are met. It is clearly mentioned under the diagnostic code ICD-10, F48,0 (neurasthenia/chronic fatigue/psychosomatic conditions) that this diagnosis cannot be given until Postviral Fatigue Syndrome/Benign Myalgic Encephalomyelitis (ME,93.3)(ICD-10,1999) has been ruled out. It cannot be in anyone’s interest (clinicians, researchers, patients, healthcare officials) for doctors to classify an illness based on their personal understanding as to where an illness belongs. Such practice can lead to mistakes in investigation, diagnosis and treatment. In addition it will lead to incorrect information in the medical records, skews the prevalence numbers and leads to problems in comparing research studies etc.

4.1  3. The illness is approved as its own entity in other countries

The following information shows the illness is approved as its own entity in several countries.


Now deceased, Professor Viggo Faber MD, knew the illness very well and states the following in one of his articles:

”… involvement of  f.ex. ME/CFS among the somatoform is in contrast with many years of research in the USA and elsewhere in the western world, which has led to ME/CFS being acknowledged by the WHO …, and that one in USA and most of the European countries has noted it as a somatic illness giving entitlement to a pension…(there) are very stringent criteria for diagnosing ME/CFS.” (Faber, 2000:22).

Great Britain

In 1959 Dr Donald Acheson (later nominated Chief Medical Officer) published an extensive overview of ME entitled The Clinical Syndrome Variously called Benign Myalgic Encephalomyelitis, Iceland Disease and Epidemic Neuromyasthenia. In this overview ME is clearly seen as a clinical entity. The British Department of Health acknowledged ME as a clinical, organic entity in November 1989 (Hansard HoC: 27th November 1989: 353). Great Britain endorses the WHO ICD-10 and therefore has to follow this classification system. The diagnosis of ME was acknowledged as a distinct clinical entity by the Royal Society of Medicine in 1978 based on thorough work by Lyle and Chamberlain (1978) who had prepared an overview of epidemic neuromyasthenia (another description of ME) in the period 1934-1977. Here a citation of this by Emeritus Professor Malcolm Hooper (2007):  

”In 1978 the Royal Society of Medicine accepted ME as a nosological organic entity. The current version of the International Classification of Diseases – ICD-10, lists myalgic encephalomyelitis under G93.3-neurological conditions. It cannot be emphasised too strongly that this recognition emerged from meticulous observation and examination.” (p. 466)

”Today, many patients with fatigue as a major feature of their illness – for example cancer, chronic obstructive pulmonary disease, depression – are being diagnosed with CFS. This has led to confusion, and has left clinicians, patients and carers without recourse to proper clinical and social support.” (p. 467) 


The diagnosis was approved in Australia at the start of 1990.


In USA the situation is different because they have compiled their own clinical version of ICD. The American CDC published a summary of Chronic Fatigue Syndrome and its Classification in the ICD 31. March 2001 by Donna Dean. It can be found in the archives of Co-Cure or at the following link: 

In the summary it says that ICD-9 was published in 1975 and that the description Benign Myalgic Encephalomyelitis can be found in the alphabetical index and is referred to as code 323.9.

5.1  4. The illness was accepted and treated a long time ago in Norway – before 1990

ME is a syndrome diagnosis, and it has been documented that ME was accepted in Norwegian neurology from before 1990. In an article in Tidsskrift for Den Norske Lægeforening (1991;111(2):232) ( Journal for The Norwegian Medical Association) a neurologist, chief consultant  Ragnar Stien MD, employed by the Rikshospitalet in the neurology department, confirms that fatigue/tiredness is not a new condition. Dr Stien thought that the Fatigue Syndrome could partly have an organic cause. He thought that the most correct description to use was Post Viral Fatigue Syndrome, a diagnosis he himself had given to a number of patients. Dr Stien demanded that there was extreme asthenia, the patient had muscle pain during physical activity and evidence  pointing to a viral infection before. He had examined 20-30 patients with this illness presentation in the 1980s. His impression was that the patients affected suffered from ”abnormally strong fatigability” (p. 232). They had to rest ”hours after minimal exertion”. Even though at that time there was no scientific evidence to rely on, Dr Stien felt that the patients were so severely affected that the cause was organic. 

Professor and specialist in general practice medicine, Dr Even Lærum, employed at the Institute of General Practice Medicine, Oslo, underlined the importance of performing a thorough physical examination. He had no objection in using the diagnosis of Chronic Fatigue Syndrome if the patient had extreme fatigue and one could not find other explanations. The treatment was symptom oriented, lifestyle changes and that patients should not put pressure on themselves (TNLF, 1991;111(2):232).The use of the diagnosis was also implemented at the same time by the Neurology department, Haukeland University Hospital. Dr Aarli and Dr Haukenes published an article on the illness in 1995. Here is an extract from this article:    

”All experience so far has shown that this illness cannot be beaten by training, because enforced training seems to make the condition worse. This is similar to Post Polio Syndrome, where it has been shown that physical training often makes the muscular weakness worse. Acknowledgement by others that the symptoms are real can be important so as to avoid adding reactive extra symptoms.” (Haukenes and Aarli, 1995:3021)

”... it is  patients who have had normal function and work capacity who after a viral illness present with considerable tiredness where causality seems to be connected to the infection as a triggering event ” (ibid.)

”It is well known that an acute infection can be followed by a fatigue syndrome that goes away. The special with this condition is that the fatigue, or exhaustion, lasts so long.” (p. 3017) 

”The clinical presentation...appears in immediate connection with an infection” (ibid.).

”Fatigue or exhaustion is the dominating symptom. Even light use of muscles brings on such a feeling of fatigue by the patient that he/she is unable to perform any type of work, often for several days. It is also characteristic that efforts and physical training worsens the fatigue. The physical fatigue has some similarities with myasthenia gravis and has led to the denomination neuromyasthenia.” (ibid., p. 3018)

The same year Dr Harald J. Hamre published an article on ME which then was called Chronic Fatigue Syndrome. Here is reproduced some of what he wrote.  

”After a thorough diagnostic clarification the patients need a stable, supportive primary care doctor contact, with intermittent diagnostic re evaluation. Support and adequate rest is crucial, based on experience. Many will be totally or partially unable to work for a long time. (Hamre, 1995:3043)

Patients with Chronic Fatigue Syndrome "can have significant and long-term relapses if they are pressed for a too high level of activity, e.g. by declaring recovery prematurely  ... They have a number of ... symptoms ... that the doctor should know and take seriously.” (ibid., p. 3044).

In 1995, Dr Kreyberg also published an article about Chronic Fatigue Syndrome. It can be read in its entirety on the Internet, and her review of the condition is not therefore referred to here: 

5. Diagnosis and necessary investigations  And So Forth

It is noted in the directorate’s report (2007) that there are strict criteria for diagnosis. In the general practice medicine it is reported that a high proportion of patients present tiredness/fatigue. Extremely few of these get a confirmed diagnosis of ME (G93.3) after years of  investigations. The general practice medicine has moreover their own coding system with various umbrella terms. The diagnostic code which is used most often in the general practice medicine is A04 (A, zero, four):

”The diagnosis is difficult because it cannot be confirmed by specific tests, laboratory tests or physical findings. The doctor has to build on the typical illness history and recognition of the clinical presentation. Fatigue is a non specific symptom in the line with fever and nausea and can be provoked by a number of factors. The aim for an operational definition must be a characterisation of this reaction so that it can be recognised clinically and can be limited against other conditions”. (Social- and Health Directorate, 2007:7)

At the Ullevål University Hospital, Medical division, a diagnosis is given based on recognised criteria (Carruthers et al, 2003; Fukuda e al. 1994) and a specific diagnostic guide which was formulated by Dr Brubakk and Dr Baumgarten. Infectious disease specialist, previously head of department at the infectious disease department at Ullevål, Dr Brubakk, is very familiar with ME/Post Viral Fatigue Syndrome (PVFS) since as long as the 1980s. 

The occurrence of ME can be compared to Multiple Sclerosis. This is also a diagnosis which demands special investigation. In Bømlo, Hordaland, there are 10 people registered with MS in the MS register. This is a municipality with 12.000 inhabitants. In the same area there are also 10 documented people with ME. In two of the families there is either ME or MS in first degree relatives. This points to clear genetic and immunological components. 

At the Haukeland University Hospital, department of neurology, where there has been a ”fatigue clinic” for 15 years, they say that disability has to be documented using validated scales such as Fatigue Severity Scale (Krupp et al, 1989), Fatigue Scale (Chalder et al, 1993) and SF-36 (Ware & Sherbourne, 1992). It is considered  very important not only to measure physical fatigue, but also cognitive fatigue, because it is often the cognitive dysfunction that patients themselves find most disabling. SF-36 is a well known tool which includes different functional dimensions. Data from a ten year period show that people with ME have fatigue scores at the highest level, from about 23-30 (extreme values) when compared to fatigue in the population (Loge, Ekeberg, Kaasa, 1998).  The ME group differs therefore clearly in having far higher scores for total fatigue than one finds in the Norwegian population. More about this can be found in the summary of the biomedical conference in Oslo in 2007 (Stormorken 2007): ):    

Reeves and colleagues at the Centres for Disease Control and Prevention (CDC, Atlanta, Georgia, USA) have explained in a scientific article a clinical, empirical approach to diagnosing and defining CFS (Reeves et al, 2005). The study showed that patients who had been classified empirically as having ME/CFS, were significantly more disabled (measured using SF-36), more severely fatigued (measured by Multidimensional Fatigue Inventory) and had more frequent and more serious accompanying symptoms than patients with medically unexplained tiredness (MUS/MUPS). The study shows that the empirical definition  (by including different fatigue scales) includes all aspects of ME/CFS which have been specified in the 1994 case definition, and  identifies people with ME/CFS in a precise manner which can easily be reproduced both by researchers and clinicians. The empirical definition makes it possible to separate ME from depression and idiopathic fatigue. That said, Jason and Richman (2007) have criticised the empirical definition.  The way Reeves and colleagues present it, it will lead to a clear broadening of the criteria in that the prevalence of ME/CFS will increase drastically, from about 800.000-1 million people to 4 million Americans. The critique against Reeves’ empirical definition can be found at the following web address:

There is a reference to Reeves et al 2007 at:

Kathrine Erdman (2008) has published an article in which she explains the biomedical abnormalities that differentiate ME/CFS from depression: Harvard-professor Anthony Komaroff has listed up to 10 central findings of biomedical abnormalities in ME/CFS: Klimas and Koneru (2007) have written an overview of last year’s advances in research. It provides a quick and easy introduction to different areas which document physiological disorders in ME and is highly recommended. ME is not unexplained, it has proven genetic factors, increased inflammation and many immunological changes. There are numerous findings, and one can no longer pretend that the biomedical research does not exist or look away from the biomedical factors in the illness presentation.  Lorusso and colleagues (2008) come now up with an article which focuses on the immunological aspects in ME/CFS. They bring forward a high level of cytokines which can explain symptoms such as fatigue and flu like feeling and which can influence NK cell activity. The authors’ hypothesis is that immunological factors form the basis for ME/CFS.  

6.1  Who is best placed at giving the diagnosis?

Medicine is based a lot on clinical experience, such has it always been, but with so few patients per general practitioner, it will not be easy to build up enough experience. Based on feedback from patients the Association feels that at present general practitioners do not treat this group of patients in a good enough way (there are exceptions). If the diagnosis is given by a general practitioner, special training is necessary. At present with a demand for a specialist evaluation in NAV (Norwegian Labour and Welfare Organisation) regulations, extensive differential diagnosis and a lot of clinical experience, the Association can support a trial period of allowing general practitioners to diagnose because there is such a long waiting list for a specialist evaluation. The Association is worried that too many will be diagnosed because general practitioners lack adequate competence (see Dr Spickett’s statements below). It is also pointed out in NAV’s circular that ”The diagnosis of the condition is difficult and labour intensive, and ruling out  normal tiredness and other illnesses can be difficult. It is therefore important to perform a thorough medical examination, especially to find out possible other illnesses that can be cured.”

Infectious disease specialist Dr Gavin Spickett (2008), specialist in immunology and lead clinician at the Royal Victoria Infirmary, Newcastle upon Tyne, stated at a ME/CFS conference in Cambridge (UK) 6. May 2008  that even though there were strict criteria for referrals to the CFS clinics, there were many who after further investigations turned out to have another diagnosis. ME is a very serious and rare condition. Because the condition is found only in 1-2 per 1000 people, a general practitioner might not have more than 1-2 people with this illness in their practice. Dr Spickett’s presentation dealt with experiences with the so called CFS centres in Great Britain. His focus was on the key role of a medical examination of patients with suspected ME/CFS. When patients were referred to the centre, they underwent a thorough clinical evaluation to rule out other diagnoses that could explain the fatigue and to make sure that patients eventually could get correct treatment if there were other diagnoses. An overview of their work showed that experienced ME/CFS clinicians find other diagnoses among a large proportion of patients with referrals due to fatigue. The centre gets unnecessary large numbers of referrals of patients presenting with fatigue with questions about ME/CFS. This is despite the strict guidelines that were developed for referrals with specifications of the examinations that should be performed beforehand. Dr Spickett and his colleagues’ experience shows that quite clear guidelines have not led to a reduction of patients who get another diagnosis in connection with investigations at the specialist centre. This is a clear indication of how difficult it is to diagnose and specialist competence is actually needed. This is especially important when there is no confirming diagnostic test and one depends on the use of internationally approved diagnostic criteria on every single patient. At present the general practitioners do not have enough knowledge of ME, some don’t even believe in the diagnosis and many have big problems in dealing with this group of patients. 

7.1  The Diagnosis is  approved by the Social Security/ NAV – strict criteria

The State Social Security informed in a circular to local social services in Norway, 30. May 1995, that the condition must be accepted as an illness. The requirement was that certain criteria had to be fulfilled (Holmes criteria, 1988; Fukuda criteria, 1994). The State Social Security (now NAV) thought that this would involve a small amount of cases and these had to be evaluated in a wholly concrete manner. Dr Haukenes and Dr Aarli (1995) thought that the diagnosis of Post Viral Fatigue Syndrome (PVFS) should be used for this type of patients, but only after a thorough clinical evaluation. Therefore there were strict criteria for diagnosis. In their article Drs Haukenes and Aarli (1995) discussed the biomedical functional abnormalities that were known at that time.

The diagnosis was officially approved by the State Social Services in 1995 with the following description: G93.3. Post-Viral Fatigue Syndrome/ Benign Myalgic Encephalomyelitis (ME):  Notification no 3/99. The illness must have brought on a considerable reduction in functional ability, i.e. more than 50 percent, where the revenue ability is reduced by more than half. The duration requirement is set to 3-4 years without sign of improvement in order to be awarded disability benefits. ME has been in the Norwegian version of ICD-10 given the diagnostic code G93.3. Before the diagnosis of ME can be given, MUPS (e.g. neurasthenia, chronic fatigue –F48.0) (ICD-10, 1991) must be ruled out. It is important to remember that both the NAV rules and regulations and the State Social Welfare law is legally binding for all healthcare personnel. The diagnosis is allowed rights in NAV’s notification that was revised 01/06.

NAV suggest that the condition should be diagnosed using criteria formulated by the Centers for Disease Control and Prevention in USA.  The CDC writes on its website that there is international concensus on the Fukuda definition, and it is used both for research and clinical use:

Internationally the Fukuda criteria have been criticised for being too broad and thereby including people with fatigue, but who do not have ME. The discontent with the Fukuda definition led to a strong need for clinical criteria. An international panel with experienced clinicians and researchers, with a mandate from Health Canada, therefore prepared clinical guidelines for diagnosis (Carruthers et al, 2003: . These guidelines reflect the patients’ situation best. President of the International Association of CFS/ME, Professor Dr Klimas PhD, has encouraged researchers and clinicians in using these, together with Fukuda criteria, in order to be able to compare research selection


Last Updated: 22 January 2010