https://projects.jira.snomed.org/browse/IHTSDO-720

Amendment History

Review Timetable

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1 Glossary

1.1 Domain Terms

2 Introduction

2.1 Purpose

Nearly one out of every two American adults age 30 and over have periodontal disease, according to recent findings from the Centers for Disease Control and Prevention (CDC).[1] The purpose of this project is to review the 41565005 |Periodontitis (disorder)| hierarchy and to evaluate and integrate requests from the American Academy of Periodontology (AAP) Classification System for Periodontal Diseases with existing 2556008 |Periodontal disease (disorder)| content in SNOMED CT^® (SCT).

2.2 Audience and stakeholder domain

The audience for this document includes all standards terminology leaders, implementers and users but is especially targeted at stakeholders involved in the practice of dentistry or concerned with oral health conditions including the American Academy of Periodontology, the Dentistry Specialty Interest Group (Dental SIG), and users of SNODENT the American Dental Association’s Systematized Nomenclature of Dentistry.

A further significant audience are the SNOMED CT authors who are tasked with implementing the recommended specification.

2.2.1 Input from stakeholders

Between the initiation of this project in 2012 and July 2015, there were over 50 requests related to periodontitis submitted to the SNOMED CT International Request Submission (SIRS) System. During that time, input related to specific concepts was also elicited from the American Academy of Periodontics representative to the SNODENT Committee and the Dentistry Specialty Interest Group (Dental SIG).

In late August 2015, after the better part of this document had been completed, an additional 84 requests related to periodontal dentistry were submitted to SIRS and are being added/evaluated for the January 2016 Release. These requests are resulting in ongoing changes in the 41565005 |Periodontitis (disorder)| hierarchy which are taken into account in this document to some degree.

2.2.2 Degree of consensus on the statement of problem

There is generally agreement that as classification systems evolve, new content needs to be added and some outdated content needs to be retired. There is consensus that, like classification systems, SNOMED CT is a work-in-progress that requires ongoing modification to its content. In addition to updating the |Periodontitis (disorder)| content, some request submissions also indicate that there is a need to clarify the concept model and the naming conventions to avoid ambiguity and duplication.

With respect to the degree of consensus on the type of content that should be added or retired, the classification system that is the basis for a significant number of the requests being addressed was developed during the International Workshop for a Classification of Periodontal Diseases and Conditions (IWCP) October 30th – November 2nd 1999.  It is sometimes referred to as The American Academy of Periodontology (AAP) 1999 Classification System and also as the IWCP 1999 Classification. The consensus that the content is needed is substantiated by the international authorities developing it. Correctly representing the intended meaning of the content in SNOMED CT may require additional consensus.

2.3 Impact of new July 2015 Editorial Policy guidance on recommendations

The July 2015 SNOMED CT Editorial Guide (section 6.1.3.17 Multisystem disorders) introduced changes to editorial policy that significantly impact recommendations made in this document. The July 2015 SNOMED CT international Release also included the addition of a substantive amount of new periodontal content.

This document had been largely completed prior to July 31, 2015. Therefore, although some changes were made to the document to reference the new changes to policy and content, many of the document’s observations and recommendations were impacted by the policy changes and the addition of new concepts and may no longer be applicable. However, the recommendations related to editorial policy and to specific SNOMED CT concepts should still be useful in helping to refine the new editorial policies as well as the periodontal content related to those policies.

3 Statement of the problem or need

3.1 Summary of problem or need, as reported

Content Tracker artf226141 – Periodontitis (disorder) hierarchy and periodontal disease:

Review the existing |Periodontitis (disorder)| hierarchy and alignment of new content requests from the American Academy of Periodontology (AAP) Classification System for Periodontal disease with existing SNOMED CT content.

3.2 Summary of requested solution

3.2.1 Review the existing |Periodontitis (disorder)| hierarchy

Review of the existing |Periodontitis (disorder)| hierarchy will require normal quality assurance processes which include;

1. Review of FSNs for ambiguity and duplicates.

2. Review of Descriptions for appropriate synonymy.

3. Evaluation of the Concept Model and review of concept definitions for consistency to ensure correct representation of meaning and correct classification.

4. Review for partitioning, completeness and for removal of outdated content.

Additionally, because |Periodontitis (disorder)| is a subtype of |Periodontal disease (disorder)|, the integrity of this concept definition also requires review.

3.2.2 Specific requests for content to be added or retired

The general request to review the existing |Periodontitis (disorder)| hierarchy was accompanied a request for the alignment of new content requests from the American Academy of Periodontology (AAP) Classification System for Periodontal Disease which will be undertaken with Section 3.2.1. Additionally, two specific content requests were addressed with artf226141 on the contact tracker.

3.2.2.1 Add “Aggressive periodontitis (disorder)”

Analysis of this initial request for the addition of “Aggressive periodontitis (disorder)” led to further questions regarding several existing SNOMED CT concepts which are now outdated in AAP including:

1.  

   1. Juvenile periodontitis (which has generalized and localized subtypes)

   2. Prepubertal periodontitis (which has generalized and localized subtypes)

   3. Early-onset periodontitis (which has generalized and localized subtypes)

   4. And possibly Rapidly progressive periodontitis

3.2.2.2 Retire |Refractory periodontitis (disorder)|

This concept has been retired from the AAP classification system and it was requested that it also be retired in SNOMED CT. 

3.3 Statement of problem as understood

3.3.1 Review the existing |Periodontitis (disorder)| hierarchy

During the time which has elapsed since the original project request, a number of new concepts have been added in the |Periodontitis (disorder)| hierarchy and ongoing addition of content in this hierarchy continues for January 2016. Additionally, new editorial policy guidance was introduced in August 2015 which impacts this content. The new and existing content will require review for consistency in the following areas:

3.3.1.1 Naming conventions and unambiguous Fully Specified Names (FSNs)

The |Periodontitis (disorder)| hierarchy contains some naming conventions which are new as of the July 2015 Release which will need to be evaluated in the context of existing naming conventions. In particular, use of “co-occurrent with” in concept FSNs and Descriptions is a recent development to SNOMED CT.

Patterns currently in use in the |Periodontitis (disorder)| hierarchy include:

1. Periodontitis associated with <X disorder> 

2. Periodontitis co-occurrent with < X disorder> (new pattern)

3. Periodontitis co-occurrent and due to <X disorder> (new pattern)

4. Periodontitis due to <X disorder> 

5. <X disorder> of peritonitis (disorder)

3.3.1.2 Descriptions

Descriptions will also require review for appropriate synonymy. For example, should “Periodontitis co-occurrent with <X disorder>” have the synonym “Periodontitis associated with < X disorder>”?

Example:

1. 710927004 |Periodontitis co-occurrent with cyclical neutropenia (disorder)|
   Synonym: Periodontitis associated with cyclical neutropenia
   
   
   

2. 703149000 |Periodontitis associated with cyclical neutropenia (disorder)| also exists as a separate concept.

3.3.1.3 Concept Model and Concept Definitions

The meaning of the prevalent patterns for the FSNs needs to be clearly understood so that the Concept Model for this content can be clarified and consistently applied. This is particularly true for the “Periodontitis co-occurrent with <X disorder> (disorder)” patterns discussed in Section 3.3.1.1 where new Editorial Guidance (released in August 2015) indicates, that for this pattern, both <Periodontitis> and <X disorder>  should be assigned as supertypes.

New guidance in the July 2015 Editorial Guide - Section 6.1.3.17.1 on Disorder combinations:

In this section, the guidance states that the “X co-occurrent with Y” pattern in an FSN implies “Simple co-occurrence” and that the default modeling pattern for this content is to:

This guidance has significant implications for periodontal diseases being added to SNOMED CT.  For example, it means that periodontal diseases referred to in the AAP Classification System under Periodontitis as a Manifestation of Systemic Diseases, are actually being assigned an IS_A relationship to Periodontitis and an IS_A relationship to the systemic disease that they are a manifestation of.

Example: 709469005 |Periodontitis co-occurrent with Down syndrome (disorder)|

It is assumed that this concept was added to represent the disorder shown below in the AAP Classification System of Periodontal Diseases:

Open

From: Armitage GC. Development of a Classification System for Periodontal Diseases and Conditions. Annals of Periodontology 1999 (4)

A review of the literature suggests that “Down syndrome-associated periodontitis” is referring to a periodontal condition that is present in a patient with Down’s syndrome. Under the new Editorial Guidance, 709469005 |Periodontitis co-occurrent with Down syndrome (disorder)| is modeled as a subtype of 41565005 |Periodontitis (disorder)| and of 41040004 |Complete trisomy 21 syndrome (disorder)| and has the following concept definition in the July 2015 Release:

Open

This concept, which was represented in The AAP Classification as “Periodontitis associated with Down Syndrome”, is now actually a type of Down Syndrome in SNOMED CT with associated morphologic abnormalities that include not only inflammation but also trisomy.

This is problematic because in the AAP Classification System and in the literature, the primary disorder for the concept now represented in SCT as |Periodontitis co-occurrent with Down Syndrome (disorder)| is actually “Periodontitis”. While the IS_A relationship to |Periodontitis (disorder)| appears to be correct, the IS_A relationship to 41040004 |Complete trisomy 21 syndrome (disorder)| requires further review. With an IS_A relationship to |Periodontitis (disorder)| and an IS_A relationship to 41040004 |Complete trisomy 21 syndrome (disorder)|, the FSN for the concept actually means Periodontitis and |Complete trisomy 21 syndrome (disorder)|.

Other aspects of the Concept Model that will require clarification related to the naming patterns identified in Section 3.3.1.1 include use of the |Due to|, |Associated with| and |Has definitional manifestation| attributes.

3.3.1.4 Partitioning, Completeness and Outdated Content

Ideally, the partitioning of the |Periodontitis (disorder)| hierarchy would mirror the partitioning in the AAP Classification System for Periodontal Diseases. However, a more detailed analysis (offered in Section 3.4.3) illustrates that this objective may have limitations within the SNOMED CT Concept Model.

The hierarchy also requires review for whether there are missing subtypes of |Periodontitis (disorder)| as well as whether there are currently inappropriate subtypes. A detailed comparison between the American Academy of Periodontology Classification System for Periodontal Disease and the SNOMED CT |Periodontitis (disorder)| hierarchy is provided as a starting point for this exercise (Appendix B - Analysis of SNOMED CT Coverage of the American Academy of Periodontology Classification of Periodontal Disease.) This comparison will also address the specific requests raised in artf226141 to add “Aggressive periodontitis (disorder)” to replace several previous terms which exist in SNOMED CT and to retire |Refractory periodontitis (disorder)| which has been retired from the AAP Classification System.

3.4 Detailed analysis of reported problem, including background

3.4.1 Naming conventions and unambiguous Fully Specified Names (FSNs)

The Editorial Guide Section 4.5.2.1 “Terminology structure: coded meanings” states:

The central component of SNOMED CT must be coded meanings. Each code must have a single clear and unambiguous meaning.

The use of “co-occurrent with” in concept FSNs and descriptions represents a fairly recent change in SNOMED CT and a further review of these patterns is indicated to ensure that they are unambiguously conveying the meaning of the clinical content they intend to represent.

Some prevalent FSN patterns currently in use (with examples of existing concepts) include:

1. Periodontitis associated with <X disorder>
   Example: 703149000 |Periodontitis associated with cyclical neutropenia (disorder)|

2. Periodontitis co-occurrent with <X disorder> (new pattern)
   Example: 710927004 |Periodontitis co-occurrent with cyclical neutropenia (disorder)

3. Periodontitis co-occurrent and due to <X disorder> (new pattern)
   Example: 710096000 |Periodontitis co-occurrent and due to histiocytosis syndrome (disorder)|

4. Periodontitis due to <X disorder>
   Example: 709472003 |Periodontitis due to Papillon-Lefèvre syndrome (disorder)|

5. <X disorder> of peritonitis (disorder)
   Example: 235984009 |Abscess of suppurative peritonitis (disorder)|

In the July 2015 Release, 15 FSNs in the |Periodontitis (disorder)| hierarchy have “co-occurrent”.

As of August 2015, an additional 19 SIRS requests for “co-occurrent with” content in the Periodontal Dentistry domain are being added or are under consideration for the January 2016 Release.

Examples:

SIRS Request ID: 601538 - Retire 95212006|Pregnancy gingivitis (disorder)| and add Gingivitis co-occurrent with pregnancy

SIRS Request ID: 601537 - Retire 700240005|Gingivitis associated with menstrual cycle (disorder)| and add Gingivitis co-occurrent with menstrual cycle

A general review of the meaning of co-occurrence suggests that the meaning can differ depending on the definition used and the context in which it is used. A few common definitions include:

1. Co-occurrence - the fact of two things happening at the same time[2]

2. Co-occurrence - an event or situation that happens at the same time as or in connection with another[3]

3. Co-occurrence - the temporal property of two things happening at the same time; "the interval determining the coincidence gate is adjustable"[4]

Additionally, a review of the literature indicates that it can be difficult to clearly define what “co-occurrence” and related constructs mean in a clinical context. “Co-occurrence” is often used in conjunction with the term “comorbid”. Wikipedia addresses the issue of comorbidity and co-occurrence in a bit more detail than most other sources but the definitions still vary. [5]

The most consistent aspect of most definitions/uses of “co-occurrence” appears to be a temporal association between two things. A significant question related to comorbidity in medicine is whether the comorbid conditions are temporally related but are otherwise independent of one another or whether the two conditions are somehow clinically related. The paper “Defining Comorbidity: Implications for Understanding Health and Health Services”[8] attempted to study the meaning of comorbidity and states,

A key question when representing disorder combinations in SNOMED CT is whether one of the disorders is the primary disorder (or index condition). Therefore, the distinction between the use of “co-occurrence with” and “associated with” for SNOMED CT disorder combinations requires further review in the context of the disorders being represented.

Interestingly, prior to the newly added July 2015 Editorial Guidance (Section 6.1.3.17 Multisystem disorders), the only SNOMED CT editorial guidance that included the word “co-occurrence” pertained to the attribute |Associated with (attribute)|. This guidance persists in the July 2015 SNOMED CT^® Editorial Guide Section 6.1.2.3 on the |Associated with (attribute)| which states:

This guidance implies that “simple co-occurrence” between two concepts is a more general phenomena than a “clinically relevant association” between two concepts and that “simple co-occurrence” would not be sufficient to warrant a concept definition that includes 47429007 |Associated with (attribute)|.

The new July 2015 Editorial Guidance on Disorder Combinations (Section 6.1.3.17.1) suggests that “simple co-occurrence” is used when two disorders co-occur temporally but a causal relationship between them cannot be asserted.

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The guidance also states:

A potential problem with this guidance is that the notion that one of the two disorders is the primary disorder is completely lost and this may result in a shift in meaning for some disorder combinations.

The existing guidance as well as the new guidance will be relevant for developing recommendations related to FSNs with “co-occurrent” as well as for Descriptions and for Concept Definitions.

3.4.2 Descriptions

Descriptions for concepts in the |Periodontitis (disorder)| hierarchy will require review for appropriate synonymy.

As noted, the Editorial Guide (Section 6.1.2.3) states that “|Associated with| represents a clinically relevant association beyond simple co-occurrence”.  The new editorial guidance (Section 6.1.3.17.1) also states that “X co-occurrent with Y” means “simple concurrence”. On this basis, the synonym “Periodontitis associated with <X disorder>” is more specific than the FSN “Periodontitis co-occurrent with <disorder>” and should not be allowed per the July 2015 Editorial Guide Section 7.4.3 Narrower synonyms:

Example:

710927004 |Periodontitis co-occurrent with cyclical neutropenia (disorder)|

Synonym: Periodontitis associated with cyclical neutropenia

All but one of the 14 concepts with the pattern “Periodontitis co-occurrent with <disorder>” have a synonym of “Periodontitis associated with <disorder>”.

Additionally, one concept with “due to” in its FSN has a more general “associated with” synonym.

3.4.3 Concept Model and Concept Definitions

Clear understanding of, and consensus on, the meaning of FSN naming patterns is essential for content in the |Periodontitis (disorder)| hierarchy so that Concept Model guidance is clear and is applied consistently across concept definitions. As discussed in Section 3.3.1.3, the new editorial guidance for “X co-occurrent with Y” is that the default modeling pattern for this content is to: “Assign each participating disorder as a supertype (or ensure that each participating disorder is present in the ancestor tree following classification).”

Consistent with this guidance, the prevalent approach for modeling “Periodontitis co-occurrent with <X disorder >” includes an |IS_A| relationship to <Periodontitis> and an |IS_A| relationship to <X disorder>.

Example: (July 2015 release)

710926008 |Periodontitis co-occurrent with familial neutropenia (disorder)| has the parents shown:

Open

If this concept is taken in the context of the AAP concept which it is intended to represent, the concept added in SNOMED CT as 710926008 |Periodontitis co-occurrent with familial neutropenia (disorder)| is classified in AAP under “Periodontitis as a Manifestation of Systemic Disease.” In AAP, this category is for “destructive periodontal disease that is a manifestation of certain systemic diseases”[11]. The concept in SNOMED should mirror the AAP meaning and be a subtype of |Periodontitis (disorder)| but not of the “Systemic Disease” that it is a manifestation of.

Open

“Periodontitis co-occurrent with familial neutropenia” represents a shift in meaning from “Periodontitis as a manifestation of familial neutropenia”. Per the meaning conveyed for this concept in the AAP Classification, the IS_A relationship to |Periodontitis (disorder)| is correct but the IS_A relationship to |Familial neutropenia (disorder)| is not.

3.4.3.1 Concept Model for disorders that include combinations of “Periodontitis” and “<X disorder>”  

The modeling of Periodontitis concepts that include a reference to an additional disorder (<X disorder>) should be determined by the meaning of the concept. A discussion of some of the critical patterns in the periodontitis hierarchy and the editorial guidance related to naming and modeling these patterns is presented here.

1.) Periodontitis co-occurrent with <X disorder> (meaning “simple co-occurrence” - where the co-occurrence represents only temporal overlap between the two disorders and no causation is implied and neither disorder is the primary disorder)

Following new guidance in the July 2015 Editorial Guide:

Periodontitis co-occurrent with <X disorder> would be modeled as:

Sufficiently Defined

=== 41565005 |Periodontitis (disorder)| + |<X> (disorder)|

And would have a concept definition that is equivalent to:

Periodontitis AND <X disorder> which would also be modeled as:

Sufficiently Defined

=== 41565005 |Periodontitis (disorder)| + |<X> (disorder)|

Periodontitis co-occurrent with <X disorder> is a new pattern in SNOMED as of the July 2015 Release. The July 2015 Editorial Guide provides guidance for this pattern (Section 6.1.3.17.1 on Disorder combinations) which suggests that “simple co-occurrence” is used when two disorders co-occur (temporally) but no causal relationship between them is asserted.

Open