Research Review By Dr. Demetry Assimakopoulos©

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Date Posted:

July 2019

Study Title:

Chronic Pain as a Symptom or a Disease: the IASP Classification of Chronic Pain for the International Classification of Diseases (ICD-11)

Authors:

Treede R-D, Reif W, Barke A et al.

Author's Affiliations:

First three authors: Medical Faculty Mannheim of Heidelberg University, Mannheim, Germany; Division of Clinical Psychology and Psychotherapy, Department of Psychology, Philipps-University Marburg, Marburg, Germany; Centre for Neuroscience and Trauma, Wingate Institute of Neurogastroenterology, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary, University of London, United Kingdom.

Publication Information:

Pain 2019; 160(1): 19-27.

Background Information:

Pain is one of the most frequent issues for patients to seek medical care and is a ubiquitous and growing concern for all involved - from patients to health care providers to policy-makers and tax payers (1, 2). The 2013 Global Burden of Disease study identified chronic low back pain as the single greatest cause of disability worldwide, followed by major depressive disorder and a number of other MSK-related pain disorders (3).

In spite of the above-mentioned findings, The International Classification of Diseases (more commonly known as the ICD) does not systematically represent chronic pain diagnoses with appropriate codes as indicators for multimodal pain management (4-6). This lack of appropriate ICD codes contributes to the paucity of clearly defined treatment pathways for patients with chronic pain. Some pain specialists have, in fact, argued for recognition of chronic pain as a disease in its own right (7). As such, a systemic classification of chronic pain was developed by a task force of the International Association for the Study of Pain (IASP). The goals of the taskforce were to create a new set of codes to distinguish chronic primary and secondary pain syndromes, while integrating pain severity, temporal course, psychosocial factors and existing diagnoses (including headaches) into the ICD coding. These pain diagnoses have been implemented in the 11th version of the ICD that was released by the World Health Organization (WHO) in June 2018.

Summary:

Chronic pain was defined previously as pain that persists past normal healing time and hence lacks the acute warning function of physiological nociception. Unfortunately, this definition is difficult to verify in many chronic musculoskeletal or neuropathic pain conditions, apart from post-operative pain and migraine headaches. As such, the authors applied a purely temporal criterion into this new definition: chronic pain is pain that lasts or recurs longer than 3 months (8). Chronic Pain is now the “parent code” for 7 other codes that comprise the most common clinically relevant groups of chronic pain conditions, which are described below.

1) Chronic Primary Pain (CPP):

CPP is defined as pain in one of more anatomical regions that persists or recurs for longer than 3-months and is associated with significant emotional distress or functional impairment. A primary criterion is that the pain in CPP cannot be accounted for by any other chronic pain condition (9). This diagnostic category is entirely new and is best suited to classify chronic pain conditions that are diagnostic entities in their own right, such as chronic widespread pain (ex. Fibromyalgia), complex regional pain syndrome, chronic primary headache (migraines), orofacial pain (TMD disorder), chronic primary visceral pain (ex. irritable bowel syndrome) and chronic primary MSK pain (ex. non-specific low back pain). Chronic secondary pain syndromes are important differential diagnoses. The underlying mechanisms of CPP may be explained by the recently proposed definition of “nociplastic pain” that was accepted into the IASP Taxonomy in 2017.

Chronic Secondary Pain Syndromes (CSPS)

CSPS are pain conditions that occur as a product or symptom of an underlying disease. In many cases, the pain may persist after successful treatment of the initial cause; in these cases, the pain diagnosis will remain the same, even after the diagnosis of underlying disease is no longer relevant. After longer periods, whereby clear evidence of dissociation between medical causes and chronic pain, a change of the chronic pain diagnosis to another category can be considered. The remaining 6 classifications are the types of CSPS.

2) Chronic Cancer-Related Pain (CCRP):

CCRP is pain that is caused by cancer itself (primary tumour or metastasis) or by its treatment (surgery, chemotherapy, radiotherapy). Pain that is caused by surgical treatment is coded in the section on chronic post-surgical pain.

3) Chronic Post-Surgical or Post-Traumatic Pain (CPSP):

This diagnostic entity depends on the initiating event being either surgical or non-surgical trauma. In both cases, pain is often neuropathic in nature, and as such, “chronic peripheral neuropathic pain” may be given as a co-diagnosis.

4) Chronic Neuropathic Pain (CNP):

Neuropathic pain, as defined by the IASP, is pain caused by a lesion or disease of the somatosensory nervous system. Neuropathic pain may be spontaneous or evoked by sensory stimuli (i.e. hyperalgesia or allodynia). CNP is divided into peripheral or central neuropathic pain. This diagnostic category requires a history of nervous system injury (i.e. stroke, nerve trauma, diabetic neuropathy) and symptomatology (i.e. pain, sensory loss, parasthesiae, hyperesthesia) that is within a neuroanatomically plausible distribution. It is necessary to demonstrate the lesion or disease involving the nervous system through imaging, biopsy or neurophysiological testing to definitively identify neuropathic pain. Questionnaires may be useful to support a clinical hypothesis of neuropathic pain, but they are not diagnostic.

5) Chronic Secondary Headache or Orofacial Pain:

This diagnostic category implies that headache or orofacial pain are a product of an underlying biomedical disease. This section interfaces with the International Headache Society (IHS) headache classification, which differentiates between primary (idiopathic) and secondary (symptomatic) headaches and orofacal pains. The IHS definition of chronic headache and orofacial pains are pains that occur for more than 2 hours per day on at least 50% of the days during the last 3-months. The list of chronic primary headaches (such as migraine) are listed under chronic primary pain syndromes, as their presence cannot be explained by any other condition.

6) Chronic Secondary Visceral Pain:

This diagnostic category is defined as persistent or recurrent visceral pain that originates from the internal organs of the head, neck, thorax, abdomen or pelvis. Pain from the viscera are usually perceived somatically (skin, subcutis, muscle) in areas that receive the same sensory innervation as the corresponding internal organ (aka. referred visceral pain). Diagnostic entities are subdivided according to the underlying mechanism which include, mechanical factors (traction, obstruction), vascular factors or persistent inflammation. Visceral pain due to cancer is coded in the chronic cancer related pain classification noted above. Similarly, functional or unexplained visceral pains, such as irritable bowel syndrome, are coded under chronic primary pain.

7) Chronic Secondary Musculoskeletal Pain (CSMP):

CSMP is defined as nociceptive persistent or recurrent pain from bone, joint muscle and related soft tissue. Pain can be spontaneous or movement-related. These are subdivided according to the major underlying mechanism, namely persistent inflammation, infectious, autoimmune, metabolic, structural, or chronic MSK pain secondary to diseases of the motor nervous system (i.e. spasticity from spinal cord injury, or Parkinsonian-related rigidity). Well-described, yet poorly understood MSK conditions such as nonspecific back pain or chronic widespread pain are coded as chronic primary pain.

Some overlap exists between groups of chronic pain conditions and their corresponding codes. The ICD-11 corrects the issue of multiple chronic pain conditions belonging to several fields through “multiple parenting.” Multiple parenting allows one diagnosis (child) to be accessed from more than one higher level diagnostic category (parent). In these cases, the child will have the same unique definition under several parent codes, allowing for greater flexibility, compared to past iterations of the ICD. “Multiple Parenting” transcends the discipline-specific structure of previous versions and allows different angles from which to approach a diagnosis. For instance, the diagnosis of chronic migraine (“child”) is listed in both the chronic secondary headache and chronic primary pain sections (“parent”). Another example may be the case of an oncologist who has diagnosed chronic neuropathic chemotherapy-induced pain (“child”) from the parent diagnostic category of cancer-related pain diagnoses, while a neurologist can render the exact same diagnosis from the chronic neuropathic pain diagnostic category.

Optional specifiers (also referred to as extension codes) are available for all chronic pain diagnoses, which allow clinicians to record pain severity, temporal course of pain, and psychosocial factors. The severity extension code is determined as a compound measure of pain intensity, pain-related distress and task interference. Pain intensity denotes the strength of the subjective pain experience (i.e. “How much does it hurt?”). Pain-related distress is defined as the multifactorial emotional aspect of pain (i.e. “How distressed are you by the pain?”). Pain-related interference describes how much the pain interferes with daily activities (i.e. “How much does the pain interfere with your life?”). Each of the severity determinates are rated by the patient on a 0-10 numerical scale, and then transformed into WHO severity categories of “mild” (NRS: 1-3; VAS: < 31 mm [code 1]), “moderate” (NRS: 4-6; VAS: 31-54 mm [code 2]), and “severe” (NRS: 7-10; VAS: 55-100 mm [code 3]). Once this is known, a patient is issued a 3-digit code. For instance, if a patient has moderate pain intensity, severe distress and mild functional interference, their case would be coded as 2:3:1. Temporal characteristics are coded as continuous, episodic/recurrent and continuous pain with pain attacks.

Significant psychological and social factors are also documented with extension codes. These factors include cognitive (i.e. catastrophizing, worry, rumination), behavioural (avoidance, endurance) and emotional (fear or anger). These extension codes should be used when psychosocial factors contribute to the onset, maintenance or exacerbation of pain, or are relevant consequences to the pain, and are available to all chronic pain diagnoses.

Clinical Application & Conclusions:

The ICD-11 is the first systematic classification system for chronic pain. The authors assembled criteria for 7 different diagnostic categories, listed above. Additionally, they added extension codes, which enable the clinician to codify and grade the intensity of pain, distress, functional interference and temporal nature of pain, based on the patient’s response to a numeric rating or visual analogue scale. The classification system is expected to improve patient access to multimodal care for all chronic pain patients, facilitate epidemiological investigation and health policy decisions, and improve funding of appropriate treatment.

Study Methods:

A Task Force for the Classification of Chronic Pain was formed by recruiting pain experts from around the world, soliciting recommendations from IASP special interest groups and topical advisory groups of the other ICD-11 sections. The scope of the chronic pain classification was developed by group consensus. Subtopics were then assigned to 7 smaller teams. Preliminary versions of the classification were published (8), presented at international conferences and were open to public comment through the IASP website and WHO proposal platform. Early versions underwent plot ecological field testing in 4 countries in 2016 (3). The prefinal version was further subjected to the official international field testing of the WHO through the IASP website.

Study Strengths / Weaknesses:

Strengths and Reviewer’s editorial: The authors discussed a pilot project which demonstrated that ICD-11 coding was much easier and more straightforward than the ICD-10. This classification system may also reduce stigma in many cultures, due to the inclusion of the chronic primary pain diagnostic entity. The ICD-11 also acknowledges the biopsychosocial nature of pain and enables clinicians to reflect this through the use of extension codes. Additionally, several diagnostic entities which were previously excluded, such as chronic cancer-related pain, chronic post-surgical pain and chronic neuropathic pain, are now included. The use of multiple parenting (of the diagnostic codes) also allows different specialists to identify the same diagnosis.

Weaknesses and Reviewer’s editorial: The ICD-11 coding system does not reflect bona-fide, pain-related DSM-5 diagnoses, such as Somatic Symptom Disorder, Factitious Disorder or Functional Neurological Disorders. This notion is important, as these complex pain-related disorders, while few and far between, may present both in community and medico-legal settings. Additionally, there is no direction from the developers of the ICD-11 on whether chronic pain sufferers can fall into two diagnostic categories simultaneously, as the etiology of a patient’s pain may be multifactorial. This might be true in cases of poly-trauma (chronic secondary MSK, visceral or headache/orofacial pains) or CRPS type-II, which can be arguably categorized as both chronic neuropathic pain and chronic primary pain. Also, while the NRS and/or VAS have been validated to grade pain severity, there has been no such validation for distress or functional interference. There were also multiple conflicts of interest on the part of the authors, which were disclosed at the end of the document.

Additional References:

  1. Mantyselka P, Kumpusalo E, Ahonen R et al. Pain as a reason to visit the doctor: a study in Finnish primary health care. Pain 2001; 89: 175–80.
  2. Goldberg DS & McGee SJ. Pain as a global public health priority. BMC Public Health 2011; 11: 770.
  3. Rice ASC, Smith BH & Blyth FM et al. Pain and the global burden of disease. Pain 2016; 157: 791–6.
  4. Fillingim RB, Bruehl S, Dworkin RH et al. The ACTTION—American Pain Society Pain Taxonomy (AAPT): an evidence- based and multidimensional approach to classifying chronic pain conditions. J Pain 2014; 15: 241–9.
  5. Finnerup NB, Scholz J, Attal N et al. Neuropathic pain needs systematic classification. Eur J Pain 2013; 17: 953–6.
  6. Rief W, Kaasa S, Jensen R, et al. The need to revise pain diagnoses in ICD-11. Pain 2010; 149: 169–70.
  7. Raffaeli W & Arnaudo E. Pain as a disease: an overview. J Pain Res 2017; 10: 2003–8.
  8. Treede RD, Rief W, Barke AJ, et al. A classification of chronic pain for ICD-11. PAIN 2015; 156: 1003–7.
  9. Nicholas M, Vlaeyen JWS, Rief W et al. The IASP Taskforce for the Classification of Chronic pain. The IASP classification of chronic pain for ICD-11: chronic primary pain. Pain 2019; 160: 28–37.