The IASP Classification of Chronic Pain for ICD-11: Chronic Primary Pain

Michael Nicholas; Johan W.S. Vlaeyen; Winfried Rief; Antonia Barke; Qasim Aziz; Rafael Benoliel; Milton Cohen; Stefan Evers; Maria Adele Giamberardino; Andreas Goebel; Beatrice Korwisi; Serge Perrot; Peter Svensson; Shuu-Jiun Wang; Rolf-Detlef Treede; The IASP Taskforce for the Classification of Chronic Pain

Disclosures

Pain. 2019;160(1):83-87. 

In This Article

Classification of Chronic Primary Pain

Many chronic pain conditions have an obscure etiology and pathophysiology, but they are characterized by a complex interplay of biological, psychological, and social factors.[15] Currently, these conditions are covered by labels such as chronic widespread pain (CWP), fibromyalgia, complex regional pain syndrome, type I (CRPS1), temporomandibular disorder (TMD), irritable bowel syndrome (IBS), and most back pain and neck pain conditions, which invariably include vague and ambiguous terms such as "nonspecific," "somatoform," or "functional." The term "chronic primary pain" was chosen after extensive consultation with the ICD-11 revision committee and is expected to have widespread acceptability, especially from a nonspecialist perspective.

The definition of the new diagnosis of CPP is intended to be agnostic with regard to etiology; in particular, it aims to avoid the obsolete dichotomy of "physical" vs "psychological,"[28] as well as exclusionary terms that define something by what is absent, such as "nonspecific." The meaning of "functional" is also ambiguous. Some take it to mean "all in the mind" and others as a "disorder of function."[54]

The introduction of "chronic primary pain" eliminates this ambiguity. Chronic primary pain is defined as pain in one or more anatomical regions that

  1. persists or recurs for longer than 3 months

  2. is associated with significant emotional distress (eg, anxiety, anger, frustration, or depressed mood) and/or significant functional disability (interference in activities of daily life and participation in social roles),

  3. and the symptoms are not better accounted for by another diagnosis.

In other words, the experience of chronic pain should be sufficiently concerning for the person to seek help for it. As in all conditions, before a diagnosis is made, it has to be ascertained whether another diagnosis better accounts for the chronic pain presentation, in which case, the diagnoses are the chronic "secondary" pain syndromes described in the companion articles: chronic cancer pain,[4] chronic postsurgical or posttraumatic pain,[45] chronic neuropathic pain,[44] chronic secondary headache or orofacial pain,[5] chronic secondary visceral pain,[2] and chronic secondary musculoskeletal pain.[35]

The General Structure of the Classification of Chronic Primary Pain

Chronic primary pain can occur in any body system (eg, nervous, musculoskeletal, and gastrointestinal systems), and in any body site (face, low-back, neck, upper-limb, thorax, abdominal, pelvis, and urogenital region), or in a combination of body sites (eg, widespread pain). This is mirrored by the general structure of the classification. Subtypes of CPP are listed in Figure 1. A complete overview of all CPP conditions as implemented in the ICD-11 foundation layer is provided in the supplementary material accompanying this article (available at http://links.lww.com/PAIN/A658).

Figure 1.

The general structure of the classification of chronic primary pain. Level 1 and 2 are part of the 2018 frozen version of ICD-11; level 3 has been entered into the foundation layer. According to the new concept of multiple parenting inICD-11, an entity may belong to more than one group of diagnoses.

In the "frozen linearization" of ICD-11, CPP receives the diagnostic code MG30.0. If, however, the subtype remains unclear, the code "chronic primary pain unspecified" (MG30.0Z) will be appropriate. We expect that the subtypes are more informative and will often be identified easily.

The Diagnostic Codes in the Classification of Chronic Primary Pain

All codes share the characteristics of CPP explained above. Specifically, it is chronic pain in one or more anatomical regions that persists or recurs for longer than 3 months and is associated with significant emotional distress and/or significant functional disability. The emotional distress can take many forms, such as demoralization, depressed mood, anxiety, anger, or frustration. Functional disability also covers a wide range of interference in daily life, such as difficulties working, sleeping, or taking part in social activities. In addition to these common features, the individual types of CPP have unique characteristics that distinguish one particular diagnosis from another.

Chronic widespread pain. Chronic widespread pain is diffuse musculoskeletal pain in at least 4 of 5 body regions and in at least 3 or more body quadrants (as defined by upper–lower/left–right side of the body) and axial skeleton (neck, back, chest, and abdomen).[9] Chronic widespread pain is characterized by the core features of CPP, such as pain persisting for at least 3 months, and associated with significant emotional distress and/or functional disability. The diagnosis is appropriate if the pain is not directly attributable to a nociceptive process in these regions, and if there are features consistent with nociplastic pain,[26] such as spontaneous or evoked pain in the affected regions, accompanied by allodynia and/or hyperalgesia and identified psychological and social contributors. Chronic widespread pain is often associated with increased medical comorbidity, including sleep disturbances, obesity, hypertension, and diabetes.[31]

Fibromyalgia syndrome: Fibromyalgia syndrome (FMS) is a form of CWP, which is defined as pain in at least 4 of 5 body regions (in at least 3 or 4 body quadrants), and is associated with sleep disorders, cognitive dysfunction, and somatic symptoms. The symptoms have been present at a similar level for at least 3 months and are not better accounted for by another diagnosis. Definitions of FMS have been repeatedly revised since it was first recognized as a rheumatic disease by WHO in 1992. Some authorities prefer to reserve the term FMS for the more severe presentations of the spectrum encompassed in CWP/FMS, but this approach reflects a quantitative rather than a qualitative distinction that depends on criteria that have yet to be validated.[20,42] Case vignette 1 features a patient with FMS.

Complex regional pain syndrome. Complex regional pain syndrome (CRPS) is a type of CPP characterized by pain in a regional distribution that usually starts distally in an extremity after trauma and that is disproportionate in magnitude or duration to the typical course (of pain) after similar tissue trauma.[6,8] The pain is spontaneous but can typically also be evoked. Complex regional pain syndrome is further characterized by signs indicating autonomic and inflammatory changes in the affected body region that may vary between patients and over time.[6] Patients can present with hyperalgesia, allodynia, skin color and temperature changes, sweating, edema, altered hair and nail growth, dystrophic skin, reduced strength, tremors and dystonia in the affected limb, and focal osteoporosis.[21] Some of these changes may be related to nociplastic mechanisms,[26] and they may change over time. At a late stage, some patients present with muscle atrophy, and joint and tendon retraction (see case vignette 2). Two subtypes of CRPS have been delineated: type 1 and type 2. Both can occur after trauma, but in CRPS type 1, there is no peripheral nerve injury, while evidence of peripheral nerve injury is required for CRPS type 2.[49] Although neuropathic mechanisms are commonly believed to be associated with CRPS type 2,[45] and nociplastic mechanisms are believed to be associated with CRPS type 1,[26] recent studies have cast doubt on the degree of difference between the 2 types of CRPS once established.[33] The definition of CRPS is also part of the ICD-11 chapter on disorders of the autonomic nervous system and cross-linked to CPP.

Chronic primary headache or orofacial pain. Chronic primary headache or orofacial pain is defined as headache or orofacial pain that occurs on at least 15 days per month for longer than 3 months. The duration of pain per day is at least 2 hours[5] (untreated), or several shorter attacks per day may occur.[34,43] Other chronic headache or orofacial pain diagnoses to be considered are listed under chronic secondary headache or orofacial pain. For most purposes, patients receive a diagnosis according to the phenotypes of headache or orofacial pain with which they currently present or with which they have presented within the last year. Each distinct type, subtype or subform of headache or orofacial pain within one patient must be separately diagnosed and coded. When a patient receives more than one diagnosis, these should be listed in the order of importance to the patient.[17,22,46] There are several subtypes of chronic primary headache or orofacial pain.

Chronic migraine: Chronic migraine is defined as headache occurring on 15 or more days/month for more than 3 months, which, on at least 8 days/month, has the features of migraine headache. Migraine is a recurrent headache disorder manifesting in attacks lasting 4 to 72 hours. Typical characteristics of the headache are unilateral location, pulsating quality, moderate or severe intensity, aggravation by routine physical activity, and an association with nausea and/or photophobia and phonophobia.[17,22,46]

Chronic tension-type headache: Chronic tension-type headache is a frequent episodic headache, which occurs for at least 2 hours per day on 15 or more days per month for more than 3 months. Typically, they are bilateral, pressing, or tightening in quality and of mild to moderate intensity, lasting hours to days, but can be unremitting. The pain does not worsen with routine physical activity but may be associated with mild nausea, photophobia, or phonophobia.[17,22,46]

Trigeminal autonomic cephalalgias: Trigeminal autonomic cephalalgias (TACs) share the clinical features of unilateral headache and, usually, prominent cranial parasympathetic autonomic features (eg, lacrimation, rhinorrhoea, nasal congestion, and eyelid oedema), which are ipsilateral to the headache. Diagnostic labels commonly used for TACs include cluster headache, paroxysmal hemicrania, short-lasting unilateral neuralgiform headache attacks, and hemicrania continua. These are considered chronic TACs if the TAC attacks persist for 1 year or longer without remission, or with remission periods lasting less than 3 months.[17,22,46]

Chronic temporomandibular disorder: Chronic TMD pain is one of the most common chronic facial pain syndromes and includes pain affecting the temporomandibular joints (TMJ) and masticatory muscles and associated tissues. Temporomandibular disorder is defined as chronic orofacial pain that occurs for at least 2 hours per day on at least 50% of the days over at least 3 months. There are at least 2 distinct phenotypes: pain in the masticatory muscles termed myofascial TMD pain, and pain in the TMJ or associated tissues termed TMJ arthralgia (see case vignette 3). There are also forms of chronic secondary TMD.[5]

Chronic burning mouth pain: Chronic burning mouth pain is chronic orofacial pain characterized by intraoral burning or dysesthetic sensation that recurs for more than 2 hours per day on 50% of the days over more than 3 months, without evident causative lesions on clinical investigation and examination. Chronic primary burning mouth pain should be distinguished from secondary burning mouth syndrome attributed to diagnoses such as candidiasis or vitamin B12 deficiency. Two separate phenotypes have been described: with and without somatosensory disturbances.[17,22,46]

Chronic primary orofacial pain: Chronic primary orofacial pain is chronic pain in the mouth and face area that is associated with significant emotional distress and/or functional disability that is not better accounted for by other diagnoses of chronic primary or chronic secondary orofacial pain.[5]

Chronic primary visceral pain. Chronic primary visceral pain is CPP localized in the head or neck, thoracic, abdominal, or pelvic region. Of note, it represents one of the major categories of internal medicine. The respective anatomical location is compatible with typical referral pain patterns from specific internal organs. Chronic primary visceral pain includes pain in the head/neck viscera of the digestive system; in the thoracic region (eg, noncardiac chest pain and reflux hypersensitivity); in the abdominal region arising from viscera of the digestive system (eg, epigastric pain syndrome, IBS, centrally mediated abdominal pain syndrome, and biliary dyskinesia) and in the pelvic region due to involvement of the viscera of the digestive, urinary, and genital systems (eg, bladder pain syndrome, anal spasm, chronic pelvic pain, and chronic testicular pain).[3,13,24,25,27,50,58] Several diagnoses that before this new classification were termed "functional" are to be subsumed under chronic primary visceral pain and have been renamed.[54] There are several subtypes of chronic primary visceral pain. These are described next.

Chronic primary chest pain syndrome: Chronic primary chest pain syndrome is recurrent primary retrosternal pain. Its anatomical location is compatible with typical referral pain patterns from esophageal origin. The pain must be present for 3 months with a symptom onset at least 6 months before the diagnosis with a frequency of at least once a week. Other esophageal symptoms such as heartburn and dysphagia must be absent. The symptoms are not better accounted for by reflux disease, other mucosal (eg, eosinophilia esophagitis) or motor processes (eg, achalasia, Jack Hammer esophagus, and diffuse esophageal spasm), cardiac causes, heartburn, dysphagia, or a diagnosis of chronic secondary visceral pain.[1] The pain is perceived in the somatic tissues of the chest wall (skin, subcutis, and muscle) in areas that receive the same sensory innervation as the esophagus (referred visceral pain) and can sometimes radiate to the arm and jaw much like angina. In these areas, secondary hyperalgesia (increased sensitivity to noxious stimuli in areas other than the primary site of the nociceptive input) may occur (see case vignette 4 for an illustration of the diagnosis).[41,59] The term "noncardiac" chest pain has been used to explain the symptoms,[14] but this is inappropriate as it is describing the pain by an absence.

Chronic primary epigastric pain syndrome: Chronic primary epigastric pain syndrome is CPP localized in the epigastric region. The distinct anatomical location is compatible with typical referral pain patterns from specific internal organs. Consistent with the ROME IV criteria, it is characterized by epigastric pain or burning that does not occur exclusively after meals, but can occur even during fasting, or even be improved after a meal. It may overlap with postprandial distress syndrome, which is associated with meal-induced dyspeptic symptoms.[48] Bothersome epigastric pain and/or burning that is severe enough to impact on usual activities must be present for at least 1 day per week over the last 3 months with symptom onset at least 6 months before diagnosis. The pain may be perceived in the somatic tissues of the abdominal wall (skin, subcutis, and muscle) in areas that receive the same sensory innervation as the small or large bowel (referred visceral pain). As with other CPP diagnoses, the diagnosis of chronic primary epigastric pain syndrome should be used unless another diagnosis would better account for the presenting symptoms and findings from investigations such as upper gastrointestinal endoscopy.[11,48] Postprandial epigastric bloating, belching, and nausea can also be present, but pain from biliary causes should be excluded. Presence of persistent vomiting should prompt the search for another disorder. Other digestive symptoms such as from gastroesophageal reflux disease and IBS may coexist with chronic primary epigastric pain.

Irritable bowel syndrome: Irritable bowel syndrome is one of the most frequent chronic primary abdominal pain conditions. Irritable bowel syndrome is a bowel disorder in which recurrent abdominal pain occurs on average for at least 1 day/week in the last 3 months and is associated with 2 or more of the following: (1) related to defecation; (2) associated with change in frequency of stool; and (3) associated with a change in form (appearance) of stool. Criteria should be fulfilled for the last 3 months with symptom onset 6 months before diagnosis. Irritable bowel syndrome subtypes may include IBS with predominant constipation or diarrhea; IBS with mixed bowel habits; and IBS unspecified.[29]

Chronic primary abdominal pain syndrome: Chronic primary abdominal pain is CPP localized in the abdominal region and associated with significant emotional distress and/or functional disability. The pain is usually continuous with no or only occasional associations with physiological events (eg, eating, defecation, or menses). Its anatomical location is compatible with typical referral pain patterns from specific internal organs, but the symptoms are not better accounted for by a diagnosis of chronic secondary abdominal pain. Chronic primary abdominal pain disorders may be associated with pathologies that have arisen secondary to changes in the control mechanisms of an organ or system and may be associated with neurobiological, physiological, and sometimes anatomical changes in the central nervous system.[2,7,11,30,48]

Chronic primary bladder pain syndrome: Chronic primary bladder pain syndrome is CPP perceived in the region of the urinary bladder that is also associated with at least one other symptom, such as worsening of the pain upon bladder filling and urinary frequency during day time and/or night time. The symptoms are not better accounted for by infection or any diagnosis of chronic secondary visceral pain. The presence of sexual dysfunction or dysfunction of the lower urinary tract should be considered.[2,12] Specific types of inflammation may be present in subsets of patients and need to be excluded. Other terms previously used include "interstitial cystitis," "painful bladder syndrome," and "PBS/IC" or "BPS/IC," but these are no longer recommended.[2,12]

Chronic primary pelvic pain syndrome: Chronic primary pelvic pain syndrome is CPP localized in the pelvic region. The anatomical location is compatible with typical referral pain patterns from specific internal organs of the pelvic area. The symptoms are not better accounted for by one of the other possible chronic secondary visceral pelvic pain diagnoses: chronic visceral pelvic pain from persistent inflammation, chronic visceral pelvic pain from vascular mechanisms, and chronic visceral pelvic pain from mechanical factors. Chronic primary pelvic pain includes pain in the pelvic region of the digestive and urogenital systems.[3,24,36,50,58]

Chronic primary musculoskeletal pain (other than orofacial). Chronic primary musculoskeletal pain is CPP located in the muscles, bones, joints, or tendons. A typical example is chronic primary low-back pain (see case vignette 5). Chronic primary musculoskeletal pain syndromes are distinguished according to location: upper (chronic primary cervical pain), middle (chronic primary thoracic pain), lower back (chronic primary low-back pain), and limbs (chronic primary limb pain). Patients may present with spontaneous or evoked pain in the affected region, accompanied by allodynia and/or hyperalgesia. Here, the conditions that were formerly named "nonspecific" musculoskeletal pain are classified.

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