These three pages are in the process of being revised. For the most recent information on classification and coding of Postviral fatigue syndrome; Myalgic encephalomyelitis; and Chronic fatigue syndrome in ICD-10 and ICD-11 see my November 2020 report:

Update on classification and coding of PVFS, ME and CFS for ICD-11, November 2020


Coding in ICD-10 for Postviral fatigue syndrome; [Benign] myalgic encephalomyelitis and Chronic fatigue syndrome

Information in Parts One and Two refers specifically to the WHO’s International ICD-10 Version: 2019. Countries using “Clinical Modifications” of ICD should refer to their own country adaptations. The classification and coding of PVFS, ME and Chronic fatigue syndrome in the US Clinical Modification, ICD-10-CM, is set out on Page 3.

Part One

International Statistical Classification of Diseases and Related Health Problems (ICD)

“ICD-10 is the major international classification of health and disease – approved by WHO’s 192 Member States at the World Health Assembly and updated by the WHO Family of International Classifications (WHO-FIC) network. ICD-10 has become the standard international diagnostic classification for all general epidemiological and many health management purposes. These include the analysis of the general health situation of population groups, and monitoring the incidence and prevalence of diseases and other health problems. ICD-10 is used to classify diseases and other conditions that are recorded on many types of health documents, including death certificates and hospital records, that provide the basis for compiling national and international mortality and morbidity statistics.” 


The current revision of ICD is Version: 2019. The WHO has stated that the 2019 update (which was released in January 2020) will be the final update in the life of ICD-10.

The Tabular List of inclusions and four-character subcategories for ICD-10 Version: 2019 can be accessed as a browser:

Tabular List ICD-10 Version: 2019

A PDF of Volume 3: Alphabetical Index for ICD-10 Version: 2019 is not available online but the browser’s search engine includes index terms.

Browsers for earlier versions are also available.

NHS England currently mandates the use of ICD-10 Version: 2016. NHS Digital has not yet decided whether or when to adopt Version: 2019 or to skip Version: 2019 and migrate directly from Version: 2016 to ICD-11 at some point after January 2022.

Browser: ICD-10 Version: 2016

PDF versions of ICD-10 (Fifth edition v 2016) Volume 1: Tabular List and Volume 3: Alphabetical Index are also available as free downloads from the WHO’s IRIS document archive: https://apps.who.int/iris/handle/10665/246208 :

ICD-10 Volume 1  Tabular List of inclusions and four-character subcategories 5th Edition 2016 [PDF]

ICD-10 Volume 2  |  Instruction Manual 5th Edition 2016 [PDF]

ICD-10 Volume 3  |  Alphabetical Index 5th Edition 2016 [PDF]


Note that ICD does not classify, code or index the composite terms “Myalgic encephalomyelitis/Chronic fatigue syndrome”; “Chronic fatigue syndrome/Myalgic encephalomyelitis”; “ME/CFS” or “CFS/ME”. 

In the context of ICD-10, ICD-11, ICD “Clinical Modifications”, DSM-IV and DSM-5 (DSM-V), this site will use only the following terms:

Postviral fatigue syndrome (PVFS)

[Benign] Myalgic encephalomyelitis (ME)

Chronic fatigue syndrome (CFS)


ICD-10 Chapter VI 

(In ICD-11, this chapter will be known as “Chapter 06”.)

For ICD-10 Version: 2019, the WHO has removed the “Benign” prefix from the Tabular List inclusion term, “Benign myalgic encephalomyelitis”.

Postviral fatigue syndrome and Myalgic encephalomyelitis are classified in Chapter VI: Diseases of the nervous system (the Neurological chapter).

This is how these two terms appear in the Tabular List ICD-10 Version: 2019


Chapter VI 

Diseases of the nervous system 


Other disorders of the nervous system



G93     Other disorders of brain


G93.3  Postviral fatigue syndrome

Myalgic encephalomyelitis

This is the only information that appears for these two terms in ICD-10. There are no textual definitions, descriptive characteristics or any other content. 


The indexing of Chronic fatigue syndrome

In ICD-10 “Chronic fatigue syndrome” is not included in Volume 1: Tabular List.

“Chronic fatigue syndrome” is listed in Volume 3: The Alphabetical Index and indexed to G93.3 (the same coding as for Postviral fatigue syndrome and Myalgic encephalomyelitis).

This is how “chronic fatigue syndrome” is listed in the ICD-10 Version: 2016 Volume 3: Alphabetical Index:

Syndrome – continued


– fatigue F48.0

– – chronic G93.3

– – postviral G93.3 


How does ICD-10 view the relationship between “Chronic fatigue syndrome”, Postviral fatigue syndrome and Benign myalgic encephalomyelitis?

The Introduction to ICD-10 Volume 3: The Alphabetical Index Version lists several possible relationships between a term included in the Alphabetical Index and a term included in the Tabular List to which it is indexed:

“The terms included in the category of the Tabular List are not exhaustive; they serve as examples of the content of the category or as indicators of its extent and limits. The Index, on the other hand, is intended to include most of the diagnostic terms currently in use. Nevertheless, reference should always be made back to the Tabular List and its notes, as well as the guidelines provided in Volume 2, to ensure that the code given by the Index fits with the information provided by a particular record.

“Because of its exhaustive nature, the Index inevitably includes many imprecise and undesirable terms. Since these terms are still occasionally encountered on medical records, coders need an indication of their assignment in the classification, even if this is to a rubric for residual or ill-defined conditions. The presence of a term in this volume, therefore, should not be taken as implying approval of its usage.”

According to a February 2009 response from WHO HQ Classifications, Terminology and Standards Team, terms that are listed in the Index may be:

a synonym to the label (title) of a category of ICD;

a sub-entity to the disease in the title of a category;

or a “best coding guess”

In indexing Chronic fatigue syndrome to G93.3, ICD-10 does not specify whether it views the term as a synonym, sub-entity or “best coding guess” to Postviral fatigue syndrome or to Myalgic encephalomyelitis.

Nor does it specify how it views the relationship between Postviral fatigue syndrome and Myalgic encephalomyelitis.

In the absence of specification within ICD-10 and in the absence of clarification by WHO HQ, Geneva, this site makes no assumptions about how ICD-10 views the relationship between these three terms.

What has the Classifications, Terminology and Standards Team, WHO, Geneva, said?

1] In a letter dated 16 October 2001, Dr B Saraceno, WHO HQ, Geneva, provided the following:

“I wish to clarify the situation regarding the classification of neurasthenia, fatigue syndrome, post viral fatigue syndrome and benign myalgic encephalomyelitis. Let me state clearly that the World Health Organisation (WHO) has not changed its position on these disorders since the publication of the International Classification of Diseases, 10th Edition in 1992 and versions of it during later years.

“Post viral fatigue syndrome remains under the diseases of the nervous system as G93.3. Benign myalgic encephalomyelitis is included within this category. Neurasthenia remains under mental and behavioural disorders as F48.0 and fatigue syndrome is included within this category. However, post viral fatigue syndrome is explicitly excluded from F48.0.

“The WHO ICD-10 Diagnostic and Management Guidelines for Mental Disorders in Primary Care, 1996, includes fatigue syndrome under neurasthenia (F48.0) but does not state or imply that conditions belonging to G93.3 should be included here.

“I would also like to state that the WHO’s position concerning this is reflected in its publications and electronic material, including websites. It is possible that one of the several WHO Collaborating Centres in the United Kingdom presented a view that is at variance with WHO’s position. Collaborating Centres are not obliged to seek approval from WHO for the material they publish. I understand that the Collaborating Centre concerned has now made changes to the information on their website after speaking with WHO.”  Source: ME/CFS: TERMINOLOGY: M Williams, 27 April 2009

2] In a response dated 23 January 2004, Andre l’Hours, WHO HQ, Geneva, provided the following:

“This is to confirm that according to the taxonomic principles governing the Tenth Revision of the World Health Organization’s International Statistical Classification of Diseases and Related Health Problems (ICD-10), it is not permitted for the same condition to be classified to more than one rubric as this would mean that the individual categories and subcategories were no longer mutually exclusive.”

(This confirmation related to a contemporaneous issue concerning the WHO Collaborating Centre, Institute of Psychiatry.)

3] In responses from early 2009, Dr Robert Jakob, WHO Classifications, Terminology and Standards reaffirmed that statements made in the past by Dr Saraceno and Mr l’Hours regarding coding and classification are still valid, adding that:

“there is no evidence that any change should be made to this in ICD-11”

“the same principles will apply to ICD-11”

Note that none of these responses specify ICD-10’s view of the relationship between Chronic fatigue syndrome, Postviral fatigue syndrome and Myalgic encephalomyelitis.


Myalgic encephalopathy

The term “Myalgic encephalopathy” has no classification or coding within ICD-10 Volume 1: Tabular List or Volume 3: Alphabetical Index. (The term “Myalgic encephalopathy” is included in the UK Edition of SNOMED CT terminology system, under Synonyms to SCTID: 52702003 Chronic fatigue syndrome.)

Chronic fatigue syndrome in DSM-IV and DSM-5

Chronic fatigue syndrome was not categorized in DSM-IV or in DSM-5.

Neurasthenia (classified in ICD-10 Chapter V: Mental and behavioural disorders at F48.0; ICD-10-CM: Chapter 5 at F48.8) was not categorized in DSM-IV or in DSM-5.

Fibromyalgia has a discrete classification within ICD-10 Chapter XIII: Diseases of the musculoskeletal system and connective tissue, under M79 Other soft tissue disorders, not elsewhere classified > M79.7


Continued on Page 2

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