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15 Articles in Volume 19, Issue #3
Analgesics of the Future: The Potential of the Endocannabinoid System
Buprenorphine: A Promising Yet Overlooked Tool
Chronic Pain and the Psychological Stages of Grief
Could a Personalized Approach to Therapy End the War on Pain?
Finally, A Systematic Classification of Pain (the ICD-11)
Hormone Therapy for Chronic Pain
How to Communicate with a Medical Marijuana Dispensary
Letters: Opioid Conversions; Scrambler Therapy for CRPS
MSK Pain: Time for an Enhanced Assessment Model
National Drug Use & Abuse Trends: Prescribed and Illicit
Neuroplasticity and the Potential to Change Pain Response
Should Emergency Naloxone Be in Schools?
Talking to Patients about Medical Cannabis
Utility of Pulsed Radiofrequency Ablation in Xiphodynia
When Opioid Prescriptions Are Denied

Finally, A Systematic Classification of Pain (the ICD-11)

Chronic pain finds its place in the WHO’s International Classification of Diseases. An inside look at the ICD-11's integration of chronic pain, including expanded criteria for neuropathic pain.
Pages 30-32

The World Health Organization (WHO) released a preliminary version of the 11th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-11) in June 2018.1 The ICD-11 is scheduled to go into effect in the year 2022. Among the major innovations introduced in the update of this fundamental, now fully electronic, reference for health statistics is a systematic classification of clinical conditions associated with chronic pain. The classification was developed by an interdisciplinary task force of the International Association for the Study of Pain (IASP) to remedy gaps and errors in the prior version, ICD-10.2,3 The new list of diagnostic codes covers the most common painful clinical entities and divides them into subgroups defined by etiology or affected organ system. The classification further includes a subgroup of conditions primarily characterized by pain whose underlying cause is incompletely understood. With the implementation of this systematic classification, ICD-11 takes a decisive step to better reflect the significance of chronic pain as a health problem of enormous epidemiological, economic, and sociological impact.

ICD-11 Provides Comprehensive Coverage of Clinically Relevant Painful Disorders

The classification of chronic pain is located in section MG30 of Chapter 21: Symptoms, signs, or clinical findings.1 It gathers in one place the relevant codes for the management of chronic pain, which in ICD-10 were scattered across anatomically, etiologically, or phenotypically defined disease categories.4 For example, G43: Migraine used to be listed under Episodic and paroxysmal disorders, whereas another headache disorder, G50.0: Trigeminal neuralgia, would be found under Nerve, nerve root, and plexus disorders. Important manifestations of chronic pain, for example, cancer-related pain required the use of generic codes such as R52: Other chronic pain.

The new classification defines chronic pain as persistent or recurrent pain for at least 3 months. This minimum duration is arbitrary but consistent with temporal cutoffs for other chronic conditions and conventional definitions of chronic pain in many clinical trials and health statistics.

ICD-11 distinguishes the main categories of chronic primary pain and chronic secondary pain (see Figure 1).5-12 Chronic primary pain is a novel concept originating in the insight that diseases or long-term conditions associated with chronic pain should be acknowledged in their own right, even if a clear understanding of the underlying etiology or pathophysiology is missing. It marks a deliberate move away from the practice of labeling unexplained pain a somatic symptom disorder. A diagnosis of somatic symptom disorder implies that the pain is caused by a behavioral, that is, mental condition. However, it is not appropriate to diagnose individuals with a mental disorder solely because an alternative medical cause cannot be established. Such a diagnosis should be based on positive psychiatric criteria. Chronic primary pain categories comprises the following: chronic primary pain, chronic widespread pain, chronic primary visceral pain, chronic primary musculoskeletal pain, chronic primary headache or orofacial pain, and complex regional pain syndrome.

Fibromyalgia is one of the entities characterized by chronic widespread pain while irritable bowel syndrome is an example of chronic primary visceral pain. The chronic primary headaches listed in ICD-11 comprise migraine, tension-type headache, and trigeminal autonomic cephalalgias, matching those included in the third edition of the International Classification of Headache Disorders (ICHD).13 Harmonizing ICD-11 codes with diagnoses in ICHD-3 was a shared goal of the IASP task force developing the classification of chronic pain and the International Headache Society. Additional subgrups fall under chronic secondary pain, such as cancer-related pain. See Figure 1 for full list.

Diagnostic Criteria of Neuropathic Pain Reflect the Level of Diagnostic Certainty

Similar tribute was paid to a diagnostic grading system for neuropathic pain that was recently proposed by the Special Interest Group on Neuropathic Pain (NeuPSIG) of the IASP.14,15 The current release of ICD-11 is limited to brief summary descriptions of central and peripheral neuropathic pain.1 Figure 2 shows the complete list of entities that will ultimately be incorporated under these headings. Each entry will contain information on the underlying etiology, the clinical phenotype of pain, and suitable additional investigations to support the diagnosis of neuropathic pain. The entries will specify distinct criteria for possible, probable, or definite neuropathic pain following the recommendations of NeuPSIG.14,15

These grading criteria indicate the certainty with which a lesion or disease of the somatosensory nervous system has been established as an explanation of the pain. Confidence in the diagnosis of neuropathic pain increases stepwise. History of a nervous system lesion or neurological disease in the absence of non-neural tissue damage, and a neuroanatomically plausible distribution of the pain support the assumption of possible neuropathic pain. Probable neuropathic pain requires somatosensory signs such as allodynia, hyperalgesia or sensory loss. The distribution of these signs needs to be consistent with the suspected lesion or disease. Confirmatory tests establishing the nervous system lesion or disease enable a definite diagnosis of neuropathic pain (see Figure 2).11

Novel Features in ICD-11 Benefit the Classification of Chronic Pain

One of the new functions in ICD-11 is the multiple parenting of diagnostic codes. While each code is embedded in a primary line (ancestry) of higher-order codes, it may also appear in a secondary ancestry when equally valid diagnostic allocations overlap. For example, 8B82.0: Trigeminal neuralgia is listed under MG30.51: Chronic peripheral neuropathic pain within the ancestry of MG30: Chronic pain, although the primary parent is 8B82: Disorders of trigeminal nerve in section 08: Diseases of the nervous system.11 The concept of multiple parenting facilitates the classification of painful disorders, which may be assigned to etiologically or anatomically defined disease categories in addition to chronic pain. Chronic painful chemotherapy-induced polyneuropathy is another example of overlapping categories falling under chronic pain. Its primary parent will be MG30.1: Chronic cancer-related pain, based on the etiology of the condition, but the code will also be referenced under MG30.5: Chronic neuropathic pain, based on the nature of the pain.7,11

Another feature improving the documentation of painful disorders is the option to use extension codes for recording the severity of pain, its temporal characteristics, and the presence of psychological or social factors. Pain severity will be implemented as a compound measure of pain intensity, pain-related distress and interference with daily activities. To expedite the assessment of pain-related interference, a link to the WHO’s International Classification of Functioning will be provided.16 Temporal characteristics may be coded as continuous pain, episodic recurrent pain (with painless intervals), and continuous pain with pain attacks. These extension codes can be added to indicate a patient’s special pain management needs, for example, because of the complexity of the pain phenotype or the level of disability caused by the pain.5

ICD-11 Approval and Impact

Although chronic pain is a symptom, it requires diagnostic evaluation and management efforts on a scale that calls for the inclusion of a systematic classification of disorders associated with persistent or recurrent pain in the ICD. The currently posted version of ICD-11 gives a first impression of the overall structure of this classification. Further refinements will be necessary, for example, to remove conflicts with residual codes of painful disorders from ICD-10.

The World Health Assembly is expected to vote on the adoption of the final version of ICD-11 in May 2019 (Editor's note: The WHA officially adopted the ICD-11 on May 25, 2019; to take effect in January 2022.) It is expected that its ultimate implementation by member states of the WHO will take time. Nevertheless, the integration of chronic pain in ICD-11 sends a strong signal that pain will achieve appropriate representation in this international standard for reporting diseases and health conditions. The ICD is the principal source for diagnostic codes that enable physicians of all specialties to document their efforts to combat chronic pain. The coding system also provides fundamental information for the identification of health trends and healthcare planning. It is widely hoped that the new systematic classification of chronic pain in the ICD-11 will support epidemiological, and other research that is essential for the development of future health policies. The current epidemic of opioid misuse in Northern America is a powerful reminder of the importance of collecting accurate data on pain-related morbidity and mortality.17

Last updated on: August 3, 2020
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Pain Redefined: Inside the IASP’s Updated Definition
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