IHTSDO-963: Review hierarchy for 84229001 - Fatigue (finding) and subtypes

https://projects.jira.snomed.org/browse/IHTSDO-963

Title

IHTSDO-963: Review hierarchy for 84229001|Fatigue (finding)| and its subtypes to propose revisions

Version Information

Document Author(s):	David Sperzel
Change Owner:
Content Editor:
Version:
Date Created:	11/22/2016
Document status	Draft
Related Tracker Artefact(s):	None

Document review

Reviewer	Review date	Comment

Statement of problem as requested or initially identified

The entire text of IHTSDO-963 is shown below:

"Tiredness is a synonym to Fatigue SCTID 84229001. Fatigue however, is a chronic condition whereas tiredness is something that can happen to all of us sometimes. There are other concepts Tired SCTID 224960004 and Feeling tired SCTID 314109004 and I am not sure how these should be modelled or if tiredness is perhaps a synonym to (one of) these. If you agree that Fatigue is a chronic condition Tired cannot be a subordinate concept to Fatigue. This whole subhierarchy need a revision."

Relevance to International Edition

Since 84229001|Fatigue (finding)| and its descendants currently reside in the International Edition, any revisions to this sub-hierarchy would arguably be relevant to the International Edition as well. Furthermore, the concept of “fatigue” is so universal that it is unlikely to belong in a national extension.

Agreed scope statement

The scope is confined to 84229001|Fatigue (finding)| and its descendants. In the 20160731 International Edition, this concept has nine direct children and 24 descendants. Only three of the descendants are fully defined: 82022002|Congenital debility of fetus (disorder)|, 420900006|Fatigue associated with acquired immunodeficiency syndrome (disorder)|, and 716749005|Fatigue associated with malignant neoplastic disease (finding)|.

The concept 60119000|Exhaustion (finding)| is a sibling of 84229001|Fatigue (finding)|. Although “fatigue” and “exhaustion” arguably have closely related meanings, review of the 60119000|Exhaustion (finding)| sub-hierarchy is out of scope and would presumably require a new content tracker item.

Similarly, 79915001|Fatigability (finding)| is a sibling of 84229001|Fatigue (finding)|. Although one can question whether there is a useful distinction between these two concepts, review of 79915001|Fatigability (finding)| and its single descendant is out of scope and would presumably require a new content tracker item.

Identify additional changes

Based on inspection of the fatigue sub-hierarchy in the IHTSDO Browser, the descendants of 84229001|Fatigue (finding)| are not referenced by any non-IS-A relationships. The 84229001|Fatigue (finding)| concept itself is only referenced by HAS FOCUS attributes in 709474002|Assessment of fatigue (procedure)| and 713121000|Management of fatigue (regime/therapy)|. Thus, any changes to the fatigue sub-hierarchy are unlikely to require changes to concepts in other parts of the terminology.

Although there are many other SNOMED CT concepts that contain the word “fatigue” in FSNs, these findings or disorders typically involve specific body sites and arguably should not be part of the sub-hierarchy rooted at 84229001|Fatigue (finding)|. Examples include 8614008|Vocal fatigue (finding)|, 80449002|Muscle fatigue (finding)|, and 202831001|Fatigue fracture of vertebra (disorder)|.

Solution proposed

The proposed solution focuses on using text definitions to clarify the meanings of concepts (especially the direct children of 84229001|Fatigue (finding)|), eliminating concepts in the fatigue sub-hierarchy that are arguably redundant, and revising the structure of the sub-hierarchy.

Developing text definitions

Constructing a clear and consistent sub-hierarchy for “fatigue” is difficult because patients and health care professionals often use multiple words that are sometimes treated as interchangeable and are at other times treated as having subtle but significant distinctions. Consequently, attempts to fully define the concepts in this sub-hierarchy using a description logic model are problematic. The best approach to meeting the URU (Understandable, Reproducible, and Useful) requirement is arguably to develop clear text definitions that document how different words with similar meanings are intended to be used in SNOMED CT. Since various references are likely to conflict in how they “lump” or “split” different terms, it is obviously desirable for text definitions to be based on references that provide a consistent perspective.

IHTSDO-963 asserts that fatigue “is a chronic condition” but that tiredness “is something that can happen to all of us sometimes.” It also questions whether 224960004|Tired (finding)| (which is direct child of 84229001|Fatigue (finding)|) and 314109004|Feeling tired (finding)| (which is a direct child of 224960004|Tired (finding)|) are appropriate subtypes of 84229001|Fatigue (finding)|, especially if one regards fatigue as necessarily being chronic. Thus, it is important to confirm or refute the view that fatigue is always a chronic condition. Although 13791008|Asthenia (finding)| is not specifically mentioned in IHTSDO-963, it is also a direct child of 84229001|Fatigue (finding)| and has synonyms including “General weakness” and “Lassitude.” Accordingly, another important question is whether we can find consistent distinctions among fatigue, tiredness, and asthenia. The following Google search results can shed some light on these questions:

From http://www.webmd.com/women/rm-quiz-fatigue-something-else

At some point, nearly everyone suffers from fatigue. In most cases, it's acute fatigue -- fatigue that occurs suddenly but lasts less than three months and is usually caused by lifestyle or environmental factors such as physical exertion, stress, lack of sleep, dehydration, or inadequate diet. In most cases, it's easily treated by addressing the cause: by reducing stress; getting more rest, sleep, or better nutrition; or hydrating properly.

Chronic fatigue lasts longer -- for more than a few months -- and it's more likely to be associated with an underlying medical condition.

Fatigue refers to a lack of energy. It is different from weakness, which refers to a loss of strength or power, and drowsiness, because you can feel tired without feeling drowsy or sleepy. Although people sometimes use these terms interchangeably, from a medical perspective the symptoms are distinctly different.

Chronic fatigue is one aspect of the specific medical condition chronic fatigue syndrome, but CFS involves more than just fatigue. You can have chronic fatigue without having chronic fatigue syndrome. CFS is extreme, long-term fatigue that is associated with other multiple symptoms. Also, in CFS, other possible causes of fatigue have been ruled out.

Fatigue is sometimes a side effect of psychoactive substances such as alcohol, nicotine, and caffeine. Other substances that can cause fatigue include many over-the-counter and prescription medications, including some antihistamines, blood pressure medications, steroids, tranquilizers, and painkillers as well as marijuana and many other illegal drugs.

Fatigue is a common feature of many, if not most, illnesses. This includes all the above as well as anemia; multiple sclerosis; eating disorders; autoimmune diseases (such as lupus); heart, liver, or kidney disease; and a wide variety of infections.

From http://medical-dictionary.thefreedictionary.com/acute+fatigue :

Acute fatigue a sudden onset of physical and mental exhaustion or weariness, particularly after a period of mental or physical stress. Physical factors usually include an accumulation of the waste products of muscle contractions. Boredom is a common mental factor. Recovery follows a period of rest and restoration of energy sources.

From https://en.wikipedia.org/wiki/Fatigue_(medical) :

Fatigue (also called exhaustion, tiredness, languidness, languor, lassitude, and listlessness) is a subjective feeling of tiredness which is distinct from weakness, and has a gradual onset. Unlike weakness, fatigue can be alleviated by periods of rest. Fatigue can have physical or mental causes. Physical fatigue is the transient inability of a muscle to maintain optimal physical performance, and is made more severe by intense physical exercise. Mental fatigue is a transient decrease in maximal cognitive performance resulting from prolonged periods of cognitive activity. It can manifest as somnolence, lethargy, or directed attention fatigue.

From http://www.medicinenet.com/script/main/art.asp?articlekey=26113

Tired: A feeling of a lessened capacity for work and reduced efficiency of accomplishment, usually accompanied by a sense of weariness and fatigue.

Tiredness is not a singular symptom that defines any one particular disease. Rather, tiredness can be a symptom of many different diseases and conditions. The causes of tiredness range from lack of sleep or excessive exercise to significant medical and surgical problems.

From https://www.healthlinkbc.ca/health-topics/wkfat

Weakness and fatigue are terms that are often used as if they mean the same thing. But in fact they describe two different sensations. It is important to know exactly what you mean when you say "I feel weak" or "I am fatigued" because it can help you and your doctor narrow down the possible causes of your symptoms.

Weakness is a lack of physical or muscle strength and the feeling that extra effort is required to move your arms, legs, or other muscles. If muscle weakness is the result of pain, the person may be able to make muscles work, but it will hurt.

Fatigue is a feeling of tiredness or exhaustion or a need to rest because of lack of energy or strength. Fatigue may result from overwork, poor sleep, worry, boredom, or lack of exercise. It is a symptom that may be caused by illness, medicine, or medical treatment such as chemotherapy. Anxiety or depression can also cause fatigue.

Both weakness and fatigue are symptoms, not diseases. Because these symptoms can be caused by many other health problems, the importance of weakness and fatigue can be determined only when other symptoms are evaluated.

From http://www.merriam-webster.com/medical

Medical Definition of fatigue: weariness or exhaustion from labor, exertion, or stress

Medical Definition of asthenia: lack or loss of strength: debility

Medical Definition of debility: the quality or state of being weak, feeble, or infirm; especially: physical weakness

From http://www.reuters.com/article/us-fatigued-tired-s-idUSCOL75594120070207

"It's important to recognize the difference between tiredness and fatigue, because fatigue is a marker that the body is not able to keep up," said Dr. Karin Olson, with the faculty of nursing at the University of Alberta. "The onset of the manifestations of fatigue, particularly if these are not normal states for you, should be taken seriously."

Based her observations, Olson created new definitions for tiredness, fatigue and exhaustion that she believes represent various points on an energy continuum. She describes her work in the current issue of Oncology Nursing Forum.

People who are tired, Olson explained, still have a fair bit of energy but are apt to feel forgetful and impatient and experience muscle weakness following work, which is often alleviated by rest.

People who are fatigued, on the other hand, experience difficulty concentrating, anxiety, a gradual decrease in stamina, difficulty sleeping, and increased sensitivity to light. They also may skip social engagements once viewed as important to them.

People who suffer from exhaustion, Olson has observed, report frank confusion that resembles delirium, emotional numbness, sudden loss of energy, difficulty in staying awake as well as in sleeping and complete social withdrawal.

The IHTSDO editorial staff may have access to online medical dictionaries that require paid subscriptions, such as http://stedmansonline.com and http://www.dorlands.com. If so, the definitions available from those sources may be preferable to the textual descriptions noted above. If not, the following text definitions are suggested for fatigue, tiredness, and asthenia:

Fatigue refers to a lack of energy, and it may be either acute or chronic. Fatigue may result from exertion, stress, and a wide variety of underlying medical conditions, including infections, malignancies, autoimmune disorders, anxiety, and depression. It may also be an adverse effect of medical treatments such as chemotherapy. Depending on the underlying cause, fatigue may or may not be relieved by rest.
Tiredness is a lack of energy that occurs after a period of physical or mental exertion. Tiredness is typically relieved by rest.
Asthenia or weakness is a lack of energy manifested as generalized lack of physical or muscle strength. Asthenia is not necessarily relieved by rest.

These suggested definitions are attempts to maintain reasonable distinctions among fatigue, tiredness, and asthenia or weakness – even though these terms are relatively vague and often used interchangeably. These definitions are also consistent with the current structure of the fatigue sub-hierarchy, where fatigue is more general than tiredness or weakness (which are subtypes of fatigue).

Removing redundancy

There are number of apparently redundant concepts in the fatigue sub-hierarchy that should be considered for retirement:

What is the difference between 272060000|Fatigue - symptom (finding)| and 84229001|Fatigue (finding)|?
What is the difference between 267031002|Tiredness symptom (finding)| and 224960004|Tired (finding)|?
What is the difference between 267032009|Tired all the time (finding)| and 272062008|Complaining of "tired all the time" (finding)|?

Although one could argue that all symptoms are findings but not all findings are symptoms, attempting to represent this distinction in fatigue sub-hierarchy only introduces confusion and reduces “face validity” (i.e., the degree to which the content appears reasonable and consistent on casual inspection). Accordingly, it is suggested that the following concepts be retired:

272060000|Fatigue - symptom (finding)|
267031002|Tiredness symptom (finding)|
272062008|Complaining of "tired all the time" (finding)|

Repositioning concepts in the sub-hierarchy

The following changes to the structure of the sub-hierarchy are suggested:

Consider introducing a new grouper concept called “Fatigue due to disease (finding)” to provide a parallel structure to 704369007|Fatigue due to treatment (finding)|. The new grouper concept would be a direct child of 84229001|Fatigue (finding)| and the parent of 420900006|Fatigue associated with acquired immunodeficiency syndrome (disorder)|, 716749005|Fatigue associated with malignant neoplastic disease (finding)|. To avoid introducing an intermediate primitive, the new grouper concept would need to be fully defined by adding a DUE TO attribute with a value of 64572001| Disease (disorder)|. To classify beneath the proposed new grouper concept, the above-mentioned concepts 420900006 and 716749005 would also need to be fully defined by adding appropriate DUE TO attributes. Additionally, the phrase “associated with” would need to be replaced by the phrase “due to” in the FSNs. The current primitive concept 442099003|Psychogenic fatigue (finding)| would also be made a direct child of the new grouper concept.
Make 444042007|Excessive postexertional fatigue (finding)| a child of 224960004|Tired (finding)|, in keeping with the idea that tiredness is typically preceded by exertion.
Make 161874006|Heavy feeling (finding)| a child of 13791008|Asthenia (finding)|, in keeping with the idea that weakness includes the feeling that extra effort is required to move the arms, legs, or other muscles.
Make 272036004|Complaining of debility and malaise (finding)| a child of 13791008|Asthenia (finding)|, in keeping with the idea that “debility” is a synonym for physical weakness.

Stakeholder input

The proposed solution will be reviewed by the stakeholder who originally described the problem.

Impact assessment

Errors that make the fatigue sub-hierarchy seem ambiguous and confusing will be corrected. As previously noted, only the 84229001|Fatigue (finding)| concept itself is referenced by non-IS-A attributes. Consequently, changes to the fatigue sub-hierarchy are unlikely to result in any negative side-effects in other parts of the SNOMED CT hierarchy.

Risk assessment

The risks of inaction are that the fatigue sub-hierarchy will continue to be ambiguous and confusing. The only apparent risks of making the change are that the effort will take resources away from higher priority content tracker items.

Approval process

Complete	Approved by	Approval Date
☐	Content Development Manager
☐	Chief Terminologist
☐	<Other>

Priority

☐Very high

☐High

☒Medium

☐Low

Specify the basis for the above priority assignment

This priority assignment is based primarily on the assumption that the IHTSDO will deem other content areas to be somewhat more urgent than revising the fatigue sub-hierarchy.

Content editing

The overall sequence of steps for content editing would involve retiring redundant concepts as suggested in the section entitled “Removing redundancy” and re-organizing the fatigue sub-hierarchy as suggested in the section entitled “Repositioning concepts in the sub-hierarchy.”

At a minimum, text definitions should be added for (at least) 84229001|Fatigue (finding)|, 13791008|Asthenia (finding)|, and 224960004|Tired (finding)| because understanding the distinctions among these three concepts is arguably the most important factor in rationalizing the fatigue sub-hierarchy.

Details of content changes

The details of the proposed content changes to the fatigue sub-hierarchy are depicted below:

84229001|Fatigue (finding)|
- 13791008|Asthenia (finding)|
  - 248278004|Attacks of weakness (finding)|
  - 272036004|Complaining of debility and malaise (finding)|
  - 82022002|Congenital debility of fetus (disorder)|
  - 248279007|Frailty (finding)|
  - 161874006|Heavy feeling (finding)|
    - 373931001| Sensation of heaviness in limbs (finding)|
      - 161873000| Heavy legs (finding)|
  - 18726006|Senile asthenia (finding)|
  - 148871000119109| Weakness as a late effect of cerebrovascular accident (disorder)|
- 704369007|Fatigue due to treatment (finding)|
  - 97201000119101|Fatigue due to chemotherapy or radiation therapy (finding)|
- new SCTID|Fatigue due to underlying condition (finding)|
  - 420900006|Fatigue associated with acquired immunodeficiency syndrome (disorder)|
  - 716749005|Fatigue associated with malignant neoplastic disease (finding)|
  - 442099003|Psychogenic fatigue (finding)|
- 224960004|Tired (finding)|
  - 444042007|Excessive postexertional fatigue (finding)|
  - 314109004|Feeling tired (finding)|
  - 713568000|Occasionally tired (finding)|
  - 267032009|Tired all the time (finding)|
  - 248269005|Tired on least exertion (finding)|

Manual quality check

A manual quality check can be performed by comparing the hierarchy in the editing tool to that shown above.

Automated quality check

Although an automated quality check query could be written, doing so is arguably not worth the effort due to the small size of the fatigue sub-hierarchy.

Publish to release branch

July 2017