1. Background on visceral pain
Pain originating from internal organs is a prominent symptom in medicine and among the main causes of patients' seeking medical care.11 Chronic visceral pain represents a significant portion of all forms of chronic pain, as shown by epidemiological studies.22 Community surveys demonstrate, for example, that 25% of the population have intermittent abdominal pain, 20% recurrent/chronic chest pain, and 14.8% of women have pelvic pain.1 Irritable bowel syndrome is a demonstrative condition: a cause of recurrent abdominal pain attacks, it attains a prevalence of 10% to 25%, and functional gastrointestinal disorders account for approximately 30% to 40% of all secondary care gastroenterology consultations.29 Primary dysmenorrhea, provoking intense and often disabling abdominal or pelvic pain at every menstrual cycle, is estimated to affect more than 50% of menstruating women, with 10% of them being forced to abstain from work for a few days each month and at least 30% of them failing to report any improvement with medical treatment.12 Secondary dysmenorrhea and chronic pelvic pain occur in a significant number of women with endometriosis, a disease affecting around 15% of all women in their fertile phase of life. Associated pain is more important than physical findings in determining quality of life.21,30 Chronic secondary visceral pain syndromes often do not occur in isolation, but these chronic secondary visceral pain syndromes may occur in the context of other chronic pain conditions. Thus a patient might present with multiple visceral pain syndromes (chronic gastritis and dysmenorrhea, for example) or with chronic visceral pain and other chronic pain syndromes not related to the viscera. For example, fibromyalgia is highly comorbid with several visceral pain disorders.4,5 The U.S. Congress and National Institutes of Health recently coined the term chronic overlapping pain conditions (COPCs) to describe the clinical state of significant overlap among chronic pain disorders.34 The chronic visceral pain syndromes are the chronic pain conditions that are more frequently encountered in these clusters of COPCs. Clinical studies in patients with secondary visceral pain syndromes have demonstrated that comorbid pain conditions can potentially exacerbate each other. Importantly, there is evidence that in patients with COPCs treatment of one chronic pain syndrome such as secondary visceral pain can result in improvement of another comorbid pain condition as well.5,10 From a clinical standpoint, when evaluating patients presenting with chronic secondary visceral pain syndromes, it is therefore important to assess all concurrent chronic pain conditions as well.
Because the pathophysiological links are not clear between different COPCs, for the purpose of ICD-11, each overlapping condition will need to be considered independently. Therefore, we focus here on causes of secondary abdominal pain independently of other COPCs. The prominence of visceral pain thus makes its prompt recognition and treatment mandatory in current medical practice.
Visceral pain has a specific presentation. At the onset, mostly in the first phases of the pain, it is a mainly deep, vague, and poorly defined pain sensation; it is oppressive, constrictive, or cramping, with marked accompanying neurovegetative symptoms: nausea, vomiting, pallor, sweating, and with changes in vital signs including blood pressure, heart rate, and body temperature. There are often accompanying emotional reactions such as distress and anxiety; these can be coded with so-called “specifiers” (or extension codes in ICD terminology). Subsequently, it tends to be referred to somatic structures (skin, subcutis, and muscle) in areas neuroanatomically related to the affected organ (referred visceral pain). Referred pain in the classification proposed here is coded according to the organ causing the referral.
Depending on the involved viscera, chronic visceral pain can cause mild to severe limitation in physical functioning. As a result, it may have a major impact on activities and participation in day-to-day life including mobility, interpersonal relations, sexual activity, social participation, and work (paid or unpaid). Such pain may hinder activities necessary to maintain health and hygiene.
A physical examination of the patient may demonstrate the anatomical location of the area of the pain and a referred pain concordant with referral from a specific organ. A local examination of somatic tissues in the referred area may or may not reveal superficial and/or deep hyperaesthesia, hyperalgesia, or allodynia (ie, referred pain without or with increased local sensitivity).
Investigations (eg, hematochemical analyses, endoscopies, and radiological investigations) that are necessary to confirm the diagnosis vary depending on the affected organ.
The treatment of chronic visceral pain is complex. It highly depends on the nature of the pain (primary vs secondary, see below). In the case of chronic secondary visceral pain, the treatment needs to be tailored to the mechanism and the structure involved. Preferably, the treatment should be multidisciplinary and multimodal, with approaches ranging from psychological interventions, physical therapy approaches, and integrative medicine approaches to pharmacological treatment. Pharmacological treatment may include analgesics, drugs acting onto the visceral pain mechanism (eg, antispasmodics), or pain modulators such as tricyclic antidepressants, gabapentenoids, and also the serotonin and noradrenaline reuptake inhibitor duloxetine, although the evidence is mixed.9,20
2. The need for a classification system
In the 10th edition of the International Classification of Diseases (ICD-10), the diseases that may underlie chronic visceral pain are classified in the chapters IX (diseases of the circulatory system), X (diseases of the respiratory system), XI (diseases of the digestive system), and XIV (diseases of the genitourinary system). These diseases have to be differentiated from chronic visceral pain. Although pain may accompany many of these diseases, this is not always the case–many diseases in these sections may manifest with or without pain, eg, endometriosis. Conversely, in many instances, the chronic pain may persist, although the underlying disease has been treated successfully. The existing ICD-10 classification does not recognize nor classify chronic secondary pain adequately.23,24 An improved and systematic classification of chronic visceral pain must acknowledge that, once the pain becomes chronic, it should be recognized as a health condition in its own right and should receive adequate treatment. If the original medical condition resolves, yet the chronic pain persists, the chronic secondary pain diagnosis remains appropriate. This does not preclude the possibility that—at some later stage—the judgement is made that the chronic pain condition is now better described by a chronic primary pain diagnosis. In both conditions, the appropriate treatment will be multimodal and geared to a reduction of pain and an improvement of functioning and quality of life.
3. The IASP task force ICD initiative
In an endeavour to improve the representation of chronic pain in the ICD, the International Association for the Study of Pain (IASP) established an international task force that worked closely with representatives of the World Health Organization (WHO) to develop a systematic classification of chronic pain in general, and chronic visceral pain in particular. The classification effort concentrates on chronic pain and excludes acute pain.32 It was also coordinated with the International Classification of Functioning, where pain is listed as a bodily function that should be assessed in every patient.19 Previous versions were field tested on consecutive cases in pain clinics in 2016 and as part of the WHO formal testing for consistency in 2017.
4. The classification of chronic visceral pain
Chronic pain is defined as persistent or recurrent pain that lasts for 3 months or more.33 This definition was chosen because the criterion is clear and unequivocal. In its scope, it is concordant with clinical criteria used extensively and includes a large share of relevant conditions. Importantly, the IASP classification of chronic visceral pain for ICD-11 also takes into account the already widely established taxonomies for the chronic visceral pain syndromes such as the ROME criteria for primary visceral pain syndromes7,16,25,28 as well as criteria for interstitial cystitis and bladder pain syndromes.2,8 The new IASP classification of chronic pain for ICD-11 will provide an umbrella classification system for all chronic pain syndromes.
4.1. The general structure of the chronic pain classification: chronic primary and chronic secondary visceral pain
Chronic visceral pain is localized in the head or neck, thoracic, abdominal, or pelvic region, where the somatic pain location is compatible with typical referral pain patterns from specific internal organs. Chronic visceral pain–along with chronic headache and orofacial pain as well as chronic musculoskeletal pain–was split into the domains of chronic primary and chronic secondary pain. Chronic primary and secondary visceral pains are often associated with significant emotional distress (such as anger, anxiety, and depression) and functional disability (interference in everyday life, reduced participation, and effect on cognition). The presence of pain catastrophizing that is often associated with emotional distress may adversely affect prognosis,17 whereas resilience and optimism might buffer individuals from the negative effects of living with chronic pain conditions.13 A diagnosis of chronic primary visceral pain should be given if the chronic pain condition is considered to have a multifactorial etiology and is believed to originate from internal organs for which no underlying pathology/cause can be identified, and hence, symptoms are not better explained by any of the other chronic visceral pain diagnoses in the secondary domain, ie, chronic visceral pain from persistent inflammation, from vascular mechanisms, from mechanical factors, and by chronic visceral cancer pain (cancer pain is dealt with separately in its own chapter3). The diagnosis of chronic primary visceral pain is appropriate even if there are identified biological or psychological contributors unless one of the other diagnoses would better account for the presenting symptoms. For a more detailed description, please refer to the companion paper on chronic primary pain.18
4.2. The classification of chronic secondary visceral pain
Chronic secondary visceral pain is persistent or recurrent pain originating from internal organs of the head or neck region or of the thoracic, abdominal, and pelvic cavities. It is often associated with emotional, cognitive, and behavioural disability. The visceral etiology of the pain should be highly probable; if it is vague, codes in the section of chronic primary pain are more appropriate. For a representation of the structure of chronic secondary visceral pain see Figure 1; a complete overview of all chronic secondary visceral pain conditions as implemented in the ICD-11 foundation layer can be found in the supplementary table (available at http://links.lww.com/PAIN/A658).
The physical examination of the patient should demonstrate an anatomical location of the area of pain concordant with the distribution of pain from a specific organ. Additional diagnostic tests depend on the affected organs and the underlying pain mechanisms (see below).
The treatment is performed along 2 main lines: (1) treatment of the pain itself (symptomatic) and (2) removal of the underlying cause or pathology if identifiable or possible. A multidisciplinary approach involving physicians with expertise in viscera (eg, specialists in internal medicine or gynaecology, urology, gastroenterology, etc.) together with pain management specialists, psychologists, and physiotherapists may be helpful in the management of complex conditions. Symptomatic treatment is primarily pharmacological, using analgesics mostly nonsteroidal anti-inflammatory drugs (NSAIDs) (eg, for dysmenorrhea) or paracetamol or pain modulators such as gabapentinoids and tricyclic antidepressants. Opioids can be used for acute pain on a short-term basis and for chronic pain for defined periods with reassessment for continuation at least every 3 months, when pain cannot be effectively controlled otherwise, keeping with current practice guidelines for their use.6,31 The treatment targeting the underlying cause or pathology varies according to the specific diseases and organs involved. It should be noted that the successful treatment of the underlying disease does not necessarily end the chronic pain.
Three main mechanisms may account for chronic secondary visceral pain, and they also structure the classification of chronic secondary visceral pain:
- (1) persistent inflammation,
- (2) vascular mechanisms, and
- (3) mechanical factors.
The WHO automatically adds a category “other” (not shown in Fig. 1), to cover the possibility that this list might not be exhaustive. If the chronic visceral pain is related to cancer or its treatment, it is classified in the section on chronic cancer-related pain3; if it is of a postsurgical or post-traumatic nature, it is classified in the respective section27; and if it is of neuropathic nature, codes in the section on chronic neuropathic pain may be appropriate, eg, in spinal cord injury patients with below-level deafferentation type pains.26
Within each of the 3 sections (persistent inflammation, vascular mechanisms, and mechanical factors), the subdivisions are structured anatomically into 4 areas:
- (1) head or neck region,
- (2) thoracic region,
- (3) abdominal region, and
- (4) pelvic region.
4.2.1. Chronic visceral pain from persistent inflammation
This type of chronic secondary visceral pain is due to long-lasting inflammation of internal organs. It can be due to infectious or noninfectious agents or autoimmune causes.
Investigations may be tailored to exclude specific underlying causes such as mechanical, or vascular factors. To diagnose inflammatory conditions, investigations would include biochemical tests (in blood/serum: indices of inflammation, erythrocyte sedimentation rate, C-reactive protein; indices of bacterial infections, neutrophil leukocytosis; indices of activation of specific immune/autoimmune processes, eg, antineutrophil cytoplasmic antibodies, double stranded DNA; and indices of infections in other organic fluids (bronchial secretion, urine, feces, vaginal secretion, pleural, pericardial, and peritoneal fluid); radiological investigation X-rays, ultrasound (US), computed tomography (CT) or magnetic resonance imaging (MRI) may be used to exclude most secondary causes of visceral pain. Likewise, endoscopy, cystoscopy, and gynaecological specific evaluations such as a hysteroscopy and biopsies from the relevant areas may also be helpful in identifying most causes of visceral pain and should be used according to best practice guidelines for the region being investigated. In some severe cases where the cause is not obvious despite extensive investigations, then diagnostic surgical procedures such as laparoscopy may be used.
Specific treatments can range from pharmacologic agents directed at curing a documented infection (antibiotic, antiviral, antifungal, or antiparasitic therapy) to immunomodulating therapy in immune or autoimmune-mediated disease (eg, corticosteroids and biological products), to surgery (eg, ablation of endometriotic lesions).
In the following, examples are given for diseases that can cause chronic visceral pain in various regions. In these cases, the original code for the underlying disease and the chronic pain code should be given. Please note that some conditions, such as endometriosis due to ectopic growths, can be responsible for pain in multiple regions.
220.127.116.11. Chronic visceral pain from persistent inflammation in the head or neck region
Diseases that may give rise to chronic visceral pain from persistent inflammation in this region are, eg, Behcet disease, Wegner granulomatosis, Crohn disease, chronic pharyngitis, or chronic tonsillitis.
18.104.22.168. Chronic visceral pain from persistent inflammation in the thoracic region
Chronic visceral pain from persistent inflammation in this region may arise from inflammatory diseases affecting the cardiovascular system (eg, chronic pericarditis), respiratory system (eg, chronic pleurisy), and the upper gastrointestinal tract (eg, infectious esophagitis, ulcer of esophagus, eosiniophilic oesophagitis, or noncardiac chest pain caused by gastro-oesophageal reflux disease).
22.214.171.124. Chronic visceral pain from persistent inflammation in the abdominal region
Chronic visceral pain from persistent inflammation in this region mainly arises from inflammatory gastrointestinal diseases such as esophagitis, gastritis, duodenitis, ulcerative colitis, Crohn disease, chronic pancreatitis, chronic appendicitis, and recurrent diverticulitis. Postinfective enteropathies can be associated with chronic pain and autoimmune inflammatory conditions such as systemic lupus erythematosus and Behcet disease can also present with gastrointestinal symptoms that include chronic pain (for an illustration see Case vignette 1).
126.96.36.199. Chronic visceral pain from persistent inflammation in the pelvic region
Chronic visceral pain from persistent inflammation in this region may arise from endometriosis, recurrent cystitis and urethritis, Crohn disease, ulcerative colitis, chronic salpingitis and oophoritis, chronic pelvic inflammatory disease, infections of the uterine cervix, recurrent or chronic vaginitis, and chronic prostatitis.
4.2.2. Chronic visceral pain from vascular mechanisms
This type of chronic secondary visceral pain is due to alterations of arterial or venous blood vessels supplying the viscera of the head or neck region and the thoracic, abdominal and pelvic cavities, or pain conditions of the vascular system producing pain in other locations (eg, limbs). Chronic pain due to vascular mechanisms can be the result of a reduction of arterial blood supply to viscera due to a diseased artery or systemic hypercoagulability, vascular functional (vasospasm) alterations, or venous thrombosis. Recurrent sickle cell disease crises also fall into this category.
Chronic visceral pain from vascular mechanisms may occur in both sexes and at any stage of life, but individual diseases may be epidemiologically more prevalent in either sex or specific age groups.
Clinical investigations may include radiological examinations such as US including Doppler US, CT, or MRI. Computed tomography or MR angiograms and direct angiograms can be considered.
Specific treatment is aimed at removal of the underlying cause and pathology, which varies according to the specific diseases and organs. This can range from pharmacologic agents directed at curing a documented hypercoagulability state to vasodilators or to surgery (eg, cardiac revascularization or vascular ablation). Symptomatic treatment may include analgesics and NSAIDs. Opioids may also be required for instance in the management of acute or chronic conditions such as bleeding in an endometrial cyst or a flare of an inflammatory condition such as Crohn disease.
188.8.131.52. Chronic visceral pain from vascular mechanisms in the head or neck region
Chronic visceral pain from vascular mechanisms in this region can arise, eg, from aneurysms of the carotid artery causing compression effects.
184.108.40.206. Chronic visceral pain from vascular mechanisms in the thoracic region
Chronic visceral pain from vascular mechanisms in this region is associated with, eg, recurrent and chronic ischemic heart disease, aortic dissection, and aneurysms of the thoracic aorta.
220.127.116.11. Chronic visceral pain from vascular mechanisms in the abdominal region
Chronic visceral pain from vascular mechanisms in this region can arise from a range of diseases including chronic vascular disorders of intestine, eg, mesenteric angina, vascular entrapment syndromes such as superior mesenteric artery syndrome and median arcuate ligament syndrome (for an illustration, see Case vignette 2). Vasculitis, ie, associated with autoimmune connective tissue diseases (eg, polyarteritis nodosa) shall be coded as chronic secondary visceral pain from persistent inflammation.
18.104.22.168. Chronic visceral pain from vascular mechanisms in the pelvic region
Chronic visceral pain from vascular mechanisms in this region may arise from subacute ischemic colitis and iliac artery aneurysms.
4.2.3. Chronic visceral pain from mechanical factors
This type of chronic secondary visceral pain is deriving from (1) the obstruction of hollow viscera as a consequence of internal migrating obstacles (eg, stones) or stenosis, with dilation above the obstacle), from (2) the traction of ligaments and vessels of internal organs or (3) the external compression of internal organs.
Chronic visceral pain from mechanical factors may occur in both sexes and at any stage of life, but individual diseases may be epidemiologically more prevalent in either sex or specific age groups, depending on the epidemiology of the primary disease. For example, biliary calculosis prevails in women during their fertile phase of life, and some conditions are sex-specific (eg, traction of ovarian ligament).
Investigations may include relevant blood tests, X-rays, US, CT, and MRI scans. In some circumstances, laparoscopic examination may be required to establish the diagnosis.
Specific treatments include the removal of the underlying cause or pathology, which varies according to the specific diseases and affected organs. Treatments aimed at removing the mechanical cause that underlies the chronic pain are mostly of an interventional nature. This can range from extracorporeal shock wave lithotripsy for urinary stones to specific surgery of the structures involved. Symptomatic treatment may include spasmolytics, analgesics, NSAIDs, and eventually also opioids.
22.214.171.124. Chronic visceral pain from mechanical factors in the head or neck region
Chronic visceral pain from mechanical factors in this region can arise, eg, from a stenosis of the pharynx, or the larynx, traction of ligaments and vessels or compression of the pharynx, larynx for instance by an enlarged thyroid gland.
126.96.36.199. Chronic visceral pain from mechanical factors in the thoracic region
A number of diseases are associated with chronic visceral pain from mechanical factors in the thoracic region. These include stenosis of the oesophagus, trachea, and bronchi including traction of ligaments, vessels or lymph glands.
188.8.131.52. Chronic visceral pain from mechanical factors in the abdominal region
Chronic visceral pain from mechanical factors in this region arises from obstructions of the organs in this area such as stones obstructing the biliary or renal tracts or sclerosing cholangitis or luminal obstructions of the gastrointestinal tract or chronic intestinal pseudo-obstruction. In addition, the traction of ligaments and vessels in the area can cause chronic pain.
184.108.40.206. Chronic visceral pain from mechanical factors in the pelvic region
Chronic visceral pain from mechanical factors in this region can arise, eg, from recurrent urinary colic because of obstructions such as lithiasis of lower urinary tract, ureteric kinking or stenosis of the anus, and rectum or the traction of the ovarian ligament and the compression of the male or the female reproductive organs (for an illustration see Case vignette 3).
4.2.4. Other chronic secondary visceral pain
At every level of the classification, the WHO adds residual categories “other specified” and “unspecified.” The category “other” is used for specific diagnoses that fall in the same category but are not represented individually. On this level of the classification of chronic visceral pain, the category “other chronic secondary visceral pain” would be the umbrella term for chronic secondary visceral pain diagnoses that are due to neither persistent inflammation, vascular mechanisms, nor mechanical factors. This category may be useful to integrate future developments. In case a condition is newly identified, it has to be decided where it would be classified. An example would be degenerative neuropathies as have been identified recently in the gastrointestinal tract14,15, which may be classified (possibly with double parenting) under other chronic neuropathic pain and under other chronic secondary visceral pain. The category “unspecified” is used to provide a code for cases in which too little information is available to permit a decision about the specific diagnosis.
The codes for chronic secondary visceral pain are intended for combined use with a wide variety of diseases that may give rise to chronic pain. The disease itself should be coded as usual, and the accompanying chronic visceral pain should be assigned a code from this section. It should be noted that, as in chronic secondary musculoskeletal pain, the intensity of the pain does not have to fully correlate with the intensity of the disease process. However, it should be likely that the pain is related to the disease; otherwise a code from the section on chronic primary visceral pain should be assigned.18 Regarding chronic secondary visceral pain, in many cases, the chronic pain may resolve once the underlying condition has been treated successfully. However, there are a number of diseases that are chronic, and pain cannot be cured but needs long-term symptomatic treatment (eg, ulcerative colitis or endometriosis). In these cases, the diagnostic code for the chronic secondary visceral pain may be an important pointer that the chronic pain should receive multimodal treatment aimed at a reduction of pain intensity (if possible) but also improving daily functioning and quality of life. If the chronic visceral pain condition persists and is fully dissociated from the other medical condition, a shift to the diagnosis “chronic primary visceral pain” can be appropriate.
The codes for chronic visceral pain are particularly useful in those cases in which the chronic pain persists although the underlying disease was treated successfully. In these cases, it is appropriate to discontinue the code for the original diagnosis of the underlying disease but keep the code for chronic secondary visceral pain. This demarcates the time when chronic secondary visceral pain has become a problem in its own right that requires a specific treatment approach. In clinical practice, this may mean a referral to, or ideally inclusion of, a multimodal treatment team. Examples would be patients with inflammatory bowel disease who can have pain that persists beyond treatment of inflammation with biologicals or patients with chronic pancreatitis.
The incidence of pain as a problem in its own right in the various diseases of internal organs is currently unknown. The proposed codes for chronic secondary visceral pain are expected to lead to better epidemiological data, which can then guide the way to treatment guidelines. These future guidelines are likely to be a combination of disease-specific treatment, generic analgesic treatment, and potentially novel treatments directed at specific pain mechanisms.
Another notable issue is that, in visceral pain, we sometimes find a pathology in the abdominal cavity, which does not always correlate with the pain complaint. Furthermore, we do not always know when the patient developed the pathology in relation to the start of the pain syndrome. Thus, it might be a coincidental finding. In this context, Stratton and Berkeley30 have suggested that it may be the innervation of the endometrial foci rather than the number or location of the foci, ie, of importance for triggering pain in patients with endometriosis. Thus, although we may find a pathology in visceral pain, we might not have the right methods yet to interpret the pathology in the context of pain, as the pathology identified and its treatment are sometimes not predictive of the pain complaint. Further research is required to clarify these issues.
Furthermore, there is an issue regarding the diagnostic category if chronic pain continues after secondary causes have been treated. The authors recommend that if a causal relationship has been established between chronic pain and an underlying cause, then the original categorization as secondary pain should continue. Further research will of course clarify these issues and in particular with advances in medical science; some conditions that are currently classified as chronic primary pain may in fact change to the category of chronic secondary pain as the underlying causes are identified.
6. Summary and conclusion
In summary, chronic visceral pain may be chronic primary visceral pain if the pain is not better accounted for by a diagnosis of chronic secondary pain. It is often associated with emotional, cognitive, and behavioural disorders as well as potentially functional issues. However, psychological factors may also be present in chronic secondary visceral pain, and both primary and secondary visceral pain are characterized by a biopsychosocial interaction.
Chronic secondary visceral pain may occur because of inflammation, vascular mechanisms, or mechanical factors. Investigations may include blood tests, radiography, and laparoscopic examinations. Treatment should be focused on the general management and the removal of the underlying cause if possible. In addition a multimodal approach to the management of chronic visceral pain is encouraged to be used more broadly as chronic pain will be often associated with emotional, cognitive, and behavioural disorders.
It is hoped that the new classification with its clear distinction between chronic primary and chronic secondary visceral pain will facilitate the diagnostic process and lead to improved tailoring of treatments and more accurate epidemiological data.
Conflict of interest statement
Q. Aziz reports grants and personal fees from Grünenthal, personal fees from Allergan, outside the submitted work. M.A. Giamberardino reports personal fees from IBSA Institute Biochimique, personal fees from EPITECH Group, personal fees from Helsinn Healthcare, grants from EPITECH Group, grants from Helsinn Healthcare, outside the submitted work. A. Barke reports personal fees from IASP, during the conduct of the study. A.P. Baranowski was Chair of IASPs Taxonomy Committee and sits on the EAU Chronic Pelvic Pain Guidelines Committee. As a consequence, he has been involved in taxonomy since 2004. In her capacity as a special government employee of the Food and Drug Administration (FDA), U. Wesselmann has served as a member of the FDA Anesthetic and Analgesic Drug Products Advisory Committee. U. Wesselmann has served as a consultant for Grünenthal GmbH and Ironwood Pharmaceuticals, Inc. W. Rief reports grants from IASP, during the conduct of the study; personal fees from Heel, personal fees from Berlin Chemie, outside the submitted work. R.-D. Treede reports grants from Boehringer Ingelheim, Astellas, AbbVie, Bayer, personal fees from Astellas, Grünenthal, Bauerfeind, Hydra, Bayer, grants from EU, DFG, BMBF, outside the submitted work. The remaining author has no conflict of interest to declare.
The authors gratefully acknowledge the financial support by the International Association for the Study of Pain and the excellent discussions with Dr Robert Jakob of WHO.
Members of the Taskforce: Rolf-Detlef Treede (Chair), Winfried Rief (Co-chair), Antonia Barke, Qasim Aziz, Michael I. Bennett, Rafael Benoliel, Milton Cohen, Stefan Evers, Nanna B. Finnerup, Michael First, Maria Adele Giamberardino, Stein Kaasa, Beatrice Korwisi, Eva Kosek, Patricia Lavand'homme, Michael Nicholas, Serge Perrot, Joachim Scholz, Stephan Schug, Blair H. Smith, Peter Svensson, Johannes Vlaeyen, Shuu-Jiun Wang.
Supplemental digital content
Supplemental digital content associated with this article can be found at http://links.lww.com/PAIN/A658. SDC includes a complete reference list of the diagnoses entered into the foundation with the foundation IDs as well as the extension codes (specifier). Since the complete list is contained, the material is identical for all papers of the series.
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