Chronic Fatigue Syndrome Classification

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Chronic Fatigue Syndrome (CFS) is a poorly understood illness and there has been much debate surrounding the definition of the condition.

The exact cause of chronic fatigue syndrome has not been identified. The symptoms vary widely between individuals and there is a lack of epidemiological data on who develops the condition.

Currently, chronic fatigue syndrome cannot be identified by any specific physical symptom or test and diagnosis is therefore based on a pattern of symptoms and the exclusion of other possible causes. This requires a period of patient observation where clinical features suggestive of the condition are assessed over time.

The 2007 National Institute of Health and clinical Excellence (NICE) guidelines recommend that the following criteria should be met in diagnosing chronic fatigue syndrome:

  • Other possible causes of the condition have been excluded and symptoms have been ongoing for:
    • 4 months in an adult
    • 3 months in a child or young person

The possibility of chronic fatigue syndrome should be considered if fatigue has the following features:

  • Newly onset (not lifelong)
  • Persistent or recurrent
  • Not explained by other health issues
  • Has significantly impacted on level of activity
  • Causes malaise/fatigue after exertion, typically on a delayed basis (about 24 hours after the exertion)

In addition, one of the following features should be present:

  • Sleeping difficulties such as insomnia, over sleep, disturbed sleep
  • Muscle and joint pain across multiple sites that does not seem to be caused by inflammation
  • Headaches
  • Painful but not enlarged lymph nodes
  • Sore throat
  • Cognitive problems such as clouded thinking, lack of concentration, short term memory loss and problems with thought processing, word formation and thought planning.
  • General malaise or flu-like symptoms
  • Dizziness and/or nausea
  • Palpitations but not cardiac pathology

Symptoms that can possibly be caused by other conditions should not be attributed to chronic fatigue syndrome without exploring other diagnoses. Examples of such features include:

  • Signs of inflammatory arthritis or connective tissue conditions
  • Signs of cardiorespiratory disease
  • Significant weight loss
  • Sleep apnea
  • Lymphadenopathy
  • Hashimoto’s thyroiditis

Further Reading

Last Updated: Jul 7, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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