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The most recent version of the International Classification of Diseases, 11th Revision (ICD-11), is introducing a new approach to classifying chronic pain that stratifies it in ways which will be new to many readers of ReFlections.

It will be critical for insurance medicine professionals to understand the concepts within this new nosology as it will likely impact how underwriters assess risk and may even affect how claims are assessed and adjudicated.

This article is Part II of Dr. Harris's exploration of this new pain nosology. Part I, which was featured in the May 2019 edition of ReFlections, focused on discussing chronic pain in general as well as chronic primary pain syndromes. Part II will address chronic secondary pain syndromes.

Chronic Secondary Pain Syndromes

These pain syndromes are conditions related to other diseases, which are the underlying cause(s) of the pain presented. The proposed new ICD-11 codes become relevant as a co-diagnosis when pain issues warrant specific care; that is, when persistent pain becomes a problem in its own right above and beyond that of the causative pathology, which is not always associated with pain. In some instances, the pain might persist longer than the precipitating disorder.

• Chronic cancer-related pain¹

  This is pain caused directly by cancer (either a primary tumor or metastases) or by the treatment(s) for it. Persistent pain is generally prevalent in cancer survivors and chronic secondary pain syndromes include neuropathic and musculoskeletal pain. (Note that pain caused by chemotherapy or radiation is coded in this category. However, pain caused by surgical treatment of cancer is coded as chronic post- surgical or post-traumatic pain, described in the following section.)

• Chronic post-surgical or post-traumatic pain²

  Irrespective of projected expectations of normal healing times, pain experienced after a surgery or other trauma is considered chronic if said pain is still felt three months after the surgery or trauma (so as to maintain consistency with the new code’s definition of “parent entity”). In other words, such pain may not be reflective of persistent primary pathology. In both post-surgical and post-traumatic conditions, neuropathic disturbance is common. On average, in 30% of cases, chronic peripheral neuropathic pain may be given as a co-diagnosis.

• Chronic neuropathic pain³

  Chronic neuropathic pain is subdivided into chronic peripheral and chronic central neuropathic pain. This type of pain is caused either by a lesion affecting or by a disease involving the somatosensory nervous system. Typically, such pain is experienced in the innervation territory pertinent to the damaged nervous system structure. It may occur either spontaneously or in response to sensory stimulation.

  A diagnosis of chronic neuropathic pain requires that a patient have a history of nervous system injury, be it physical, chemical, or metabolic, the pain from which is associated with a specific neuroanatomical distribution. Similarly, associated sensory loss(es) or other neurological derangement(s) must be consistent with the innervation territory of the damaged nervous structure.

  Confirmation of chronic neuropathic pain requires identification of the lesion or disease involving the nervous system via, for example, imaging, histopathology, or neurophysiological testing. The diagnosis cannot be applied purely on the basis of obtained history.

• Chronic secondary headache or orofacial pain⁴
  
  The definitional language for this type of pain cross-references substantially with that used by the International Headache Society (IHS), which was fully implemented in ICD-11's chapter on neurology. That classification differentiates among the following:
  –– primary (idiopathic) headaches
  –– secondary (symptomatic) headaches
  –– orofacial pains including cranial neuralgias
  
  Chronic headache and orofacial pain are defined as conditions which occur for more than two hours a day and for at least 50% of the days during a minimum three-month period. This classification category includes only chronic secondary headache and chronic orofacial pain; chronic primary headache is listed under chronic primary pain syndromes. In addition, the types of chronic orofacial pain detailed in the ICD-11 classification are more varied than those in the IHS classification, and include chronic dental and temporomandibular conditions.

• Chronic secondary visceral pain⁵
  
  This type of pain is defined in ICD-11 as “persistent or recurrent pain that originates from internal organs of the head and neck region and the thoracic, abdominal, and pelvic cavities.” Such pain can be perceived in the tissues of the body wall (i.e., skin and muscle) as well as in other areas that are receiving the same sensory innervation as the internal organ(s) where the pain (“referred visceral pain”) originates. The diagnostic entities within this category are further subdivided according to the dominant underlying causative mechanisms for the pain, such as mechanical factors, vascular factors, or ongoing inflammation.
  
  Visceral pain due to cancer is classified as chronic cancer-related pain, while pain due to functional or unexplained mechanisms is classified as chronic primary pain.

• Chronic secondary musculoskeletal pain⁶

  This pain is defined as “persistent or recurrent pain that arises as part of the disease process directly affecting bone(s), joint(s), muscle(s), or related soft tissue(s).” This category is limited to nociceptive pain and therefore does not include pain experienced in musculoskeletal tissues that does not actually arise from those tissues, such as pain related to neural compression or somatic referred pain.
  
  This diagnostic category is further subdivided according to the underlying etiologic mechanisms, such as inflammation, infection, autoimmune causes, dysfunctional metabolic disturbance(s), structural or anatomical changes in the affected tissues, or chronic musculoskeletal pain secondary to diseases of the motor nervous system; e.g., spasticity after central nervous system injury or the rigidity seen in Parkinson’s disease.
  
  Pain disorders with musculoskeletal manifestation for which the cause is incompletely understood, such as non-specific pain or chronic widespread pain, are included in the section on chronic primary pain and are reviewed in Part I of this article.

Severity and Other Extension Codes In ICD-11⁷

Extension codes, which were first introduced with ICD-10, provide more details than the stem code and are available for all chronic pain conditions. These pertain to pain severity, how the pain progresses over time, and evidence of psychological and social factors in the pain state. (See Table I.)

In assessing the severity of pain states, consideration is given to subjective measures of pain intensity, pain-related distress, and pain-related functional interference. Of course, the validity of these measures can be clouded by the need to rely on subjective patient reporting. Therefore the potential exists for reported pain to be influenced by current and long-term patient attitudes and/ or beliefs (personal and cultural), patient anxiety, depression, related unconscious processes, and even perhaps conscious manipulation by the patient.

Temporal (over time) pain characteristics are to be coded as follows:

• continuous pain

• episodic recurrent pain

• continuous pain with pain attacks

Psychological factors can include evidence of problematic cognition such as catastrophization and ruminating, behaviors such as avoidance or endurance, and emotions such as fear or anger. Psychosocial factors encompass how the pain impacts the patient’s relationships with others.

The use of these extension codes is encouraged in instances where psychological or social factors are judged to contribute to the onset, maintenance, and/or exacerbation of pain, or are regarded as relevant consequences of the pain. They are not to be used to imply a causal or an etiological relationship, as all chronic pain is regarded as a multifaceted biopsychosocial phenomenon.

Table 1: Specifiers or Extension Codes in ICD-11

Source: Treede et al.⁷

Scope and Coordination

In due course, these new ICD-11 classifications are intended to be coordinated with the World Health Organization family of international classifications of various health/ morbidity factors, which also include The International Code of Functioning (ICF) and the International Code of Health Interventions (ICHI). This is seen as being of particular importance in the classification of chronic pain conditions, as both systems assess pain and any associated impairments. The draft of the functioning properties pertaining to persistent pain, based on the ICF domains, was developed jointly by the International Association for the Study of Pain (IASP) and the International Society for Physical and Rehabilitation Medicine (ISPRM).

ICD-11 Pain Nosology: Implications for Underwriting and Claims Management

Incorporation of this new classificatory system into the ICD-11, and subsequent common clinical use, may pose some challenges as medical, administrative, and related industries become accustomed to the new terminologies. We can reasonably anticipate initial uncertainty pertaining to these diagnoses. Debate may also be triggered regarding the utility and applicability of these new codes as they are incorporated into common parlance.

There is likely to be some imprecise application of the terms and codes as medical practitioners acquire familiarity with the novel and rather precise set of underlying criteria. In addition, all involved may need to query which diagnostic system has been used to reach a diagnosis, especially if imprecise terminology such as “chronic pain disorder” is used in attending physician statements.

Perhaps the sophistication of this new system will precipitate a broader interest in the hypothesis of a shared genetic, inflammatory, and/or neuroendocrine etiology of pain contributing to some psychiatric disorders as well as conditions such as chronic primary pain disorders (e.g., irritable bowel syndrome and fibromyalgia).

Some have criticized these new categories for seeming to reject psychiatric etiology as a primary contributor to certain pain states. From a clinical perspective, one might suggest that, in fact, primary pain disorder categories serve to properly integrate all facets of the individual, without laboring over insoluble questions and often pejorative and unprovable conclusions pertaining to the degree to which one factor contributes to the pain. Advancing technology may afford us more sophisticated assessment of illness in years to come and provide a basis of reconsideration of nosological classification. From an insurer’s perspective, given the lack of objective clinical information which can be gleaned in relation to some presentations, abandonment of the potential for a clearly psychiatric attribution in the ICD system may prove challenging, and could compromise the planning and provision of appropriate therapies and interventions.

In some situations, a condition may meet ICD-11 diagnostic criteria for a pain disorder while also satisfying criteria as a mental illness under the Diagnostic and Statistical Manual, Fifth Edition (DSM-5). This may invite debate as to whether or not the condition can be considered a mental illness. Insurers will need to think carefully about how they respond to such situations, and policy document wordings may warrant some preemptive adjustments. While there will be greater acceptance of terminology pertaining to chronic primary pain disorders, we should not lose sight of our current vigilance pertaining to the common association of such presentations with psychiatric vulnerabilities or even frank mental illness. Closer attention to other possible indicators of mental illness (e.g., past treatment for insomnia, family histories) may improve underwriting decisions and claims management.

A projected set of mortality and morbidity data for field testing/assessment of these categories was made available to ICD users in 2017 and updated in 2018. After consideration, the World Health Assembly endorsed the ICD-11 in May 2019.⁸ Countries around the world are now expected to start reporting health data using ICD-11 from 2022 onward. Usable mortality and morbidity data pertaining to these new diagnoses will be unavailable for several years, but once these diagnoses are formally adopted by the ICD- 11, pertinent research will fill journals, addressing questions of reliability and validity of these diagnoses, and will promote our understanding and insights into these new codes and definitions.

Conclusion

An understanding of the new nosology of chronic pain may prove essential for insurance medicine professionals as the terms are adopted in the near future. This understanding will assist in assessing risk and adjudicating claims, as well as providing insight into current biological constructs underpinning the biopsychosocial facets of chronic pain syndromes.