Chronic pain has been recognized as pain that persists past normal healing time
and hence lacks the acute warning function of physiological nociception.
Usually pain is regarded as chronic when it lasts or recurs for more than 3 to 6 months.
Chronic pain is a frequent condition, affecting an estimated 20% of people worldwide
and accounting for 15% to 20% of physician visits.
Chronic pain should receive greater attention as a global health priority because
adequate pain treatment is a human right, and it is the duty of any health care system
to provide it.
The current version of the International Classification of Diseases (ICD) of the World
Health Organization (WHO) includes some diagnostic codes for chronic pain conditions,
but these diagnoses do not reflect the actual epidemiology of chronic pain, nor are
they categorized in a systematic manner. The ICD is the preeminent tool for coding
diagnoses and documenting investigations or therapeutic measures within the health
care systems of many countries. In addition, ICD codes are commonly used to report
target diseases and comorbidities of participants in clinical research. Consequently,
the current lack of adequate coding in the ICD makes the acquisition of accurate epidemiological
data related to chronic pain difficult, prevents adequate billing for health care
expenses related to pain treatment, and hinders the development and implementation
of new therapies.
Responding to these shortcomings, the International Association for the Study of Pain
(IASP) contacted the WHO and established a Task Force for the Classification of Chronic
Pain. The IASP Task Force, which comprises pain experts from across the globe,
has developed a new and pragmatic classification of chronic pain for the upcoming
11th revision of the ICD. The goal is to create a classification system that is applicable
in primary care and in clinical settings for specialized pain management.
A major challenge in this process was finding a rational principle of classification
that suits the different types of chronic pain and fits into the general ICD-11 framework.
Pain categories are variably defined based on the perceived location (headache), etiology
(cancer pain), or the primarily affected anatomical system (neuropathic pain). Some
diagnoses of pain defy these classification principles (fibromyalgia).
This problem is not unique to the classification of pain, but exists throughout the
ICD. The IASP Task Force decided to give first priority to pain etiology, followed
by underlying pathophysiological mechanisms, and finally the body site. Developing
this multilayered classification was greatly facilitated by a novel principle of assigning
diagnostic codes in ICD-11, termed “multiple parenting.” Multiple parenting allows
the same diagnosis to be subsumed under more than 1 category (for a glossary of ICD
terms refer to Table 1). Each diagnosis retains 1 category as primary parent, but
is cross-referenced to other categories that function as secondary parents.
Glossary of ICD-11 terms.
The new ICD category for “Chronic Pain” comprises the most common clinically relevant
disorders. These disorders were divided into 7 groups (Fig. 1): (1) chronic primary
pain, (2) chronic cancer pain, (3) chronic posttraumatic and postsurgical pain, (4)
chronic neuropathic pain, (5) chronic headache and orofacial pain, (6) chronic visceral
pain, and (7) chronic musculoskeletal pain. Experts assigned to each group are responsible
for the definition of diagnostic criteria and the selection of the diagnoses to be
included under these subcategories of chronic pain. Thanks to Bedirhan Üstün and Robert
Jakob of the WHO, these pain diagnoses are now integrated in the beta version of ICD-11
(http://id.who.int/icd/entity/1581976053). The Task Force is generating content models
for single entities to describe their clinical characteristics. After peer review
overseen by the WHO Steering Committee,
the classification of chronic pain will be voted into action by the World Health Assembly
Organizational chart of Task Force, IASP, and WHO interactions. The IASP Task Force
was created by the IASP council and its scope defined in direct consultation of the
chairs (R.D.T. and W.R.) with WHO representatives in 2012. The Task Force reports
to the IASP Council on an annual basis.
2. Classification of chronic pain
Chronic pain was defined as persistent or recurrent pain lasting longer than 3 months.
This definition according to pain duration has the advantage that it is clear and
Optional specifiers for each diagnosis record evidence of psychosocial factors and
the severity of the pain. Pain severity can be graded based on pain intensity, pain-related
distress, and functional impairment.
2.1. Chronic primary pain
Chronic primary pain is pain in 1 or more anatomic regions that persists or recurs
for longer than 3 months and is associated with significant emotional distress or
significant functional disability (interference with activities of daily life and
participation in social roles) and that cannot be better explained by another chronic
pain condition. This is a new phenomenological definition, created because the etiology
is unknown for many forms of chronic pain. Common conditions such as, eg, back pain
that is neither identified as musculoskeletal or neuropathic pain, chronic widespread
pain, fibromyalgia, and irritable bowel syndrome will be found in this section and
biological findings contributing to the pain problem may or may not be present. The
term “primary pain” was chosen in close liaison with the ICD-11 revision committee,
who felt this was the most widely acceptable term, in particular, from a nonspecialist
2.2. Chronic cancer pain
Pain is a frequent and debilitating accompaniment of cancer
that as yet has not been represented in the ICD. The Task Force decided to list it
as a separate entity because there are specific treatment guidelines.
Chronic cancer pain includes pain caused by the cancer itself (the primary tumor or
metastases) and pain that is caused by the cancer treatment (surgical, chemotherapy,
radiotherapy, and others). Cancer-related pain will be subdivided based on location
into visceral, bony (or musculoskeletal), and somatosensory (neuropathic). It will
be described as either continuous (background pain) or intermittent (episodic pain)
if associated with physical movement or clinical procedures. The treatment-related
pain will be cross-referenced from the chapters on postsurgical pain and neuropathic
2.3. Chronic postsurgical and posttraumatic pain
Because pain that persists beyond normal healing is frequent after surgery and some
types of injuries, the entity of postsurgical and posttraumatic pain was created.
This is defined as pain that develops after a surgical procedure or a tissue injury
(involving any trauma, including burns) and persists at least 3 months after surgery
or tissue trauma
; this is a definition of exclusion, as all other causes of pain (infection, recurring
malignancy) as well as pain from a pre-existing pain problem need to be excluded.
In view of the different causality, as well as from a medicolegal point of view, a
separation between postsurgical pain and pain after all other trauma is regarded as
useful. Depending on the type of surgery, chronic postsurgical pain is often neuropathic
pain (on average 30% of cases with a range from 6% to 54% and more).
Pain including such a neuropathic component is usually more severe than nociceptive
pain and often affects the quality of life more adversely.
2.4. Chronic neuropathic pain
Chronic neuropathic pain is caused by a lesion or disease of the somatosensory nervous
The somatosensory nervous system provides information about the body including skin,
musculoskeletal, and visceral organs. Neuropathic pain may be spontaneous or evoked,
as an increased response to a painful stimulus (hyperalgesia) or a painful response
to a normally nonpainful stimulus (allodynia). The diagnosis of neuropathic pain requires
a history of nervous system injury, for example, by a stroke, nerve trauma, or diabetic
neuropathy, and a neuroanatomically plausible distribution of the pain.
For the identification of definite neuropathic pain, it is necessary to demonstrate
the lesion or disease involving the nervous system, for example, by imaging, biopsy,
neurophysiological, or laboratory tests. In addition, negative or positive sensory
signs compatible with the innervation territory of the lesioned nervous structure
must be present.
Diagnostic entities within this category will be divided into conditions of peripheral
or central neuropathic pain.
2.5. Chronic headache and orofacial pain
The International Headache Society (IHS) has created a headache classification
that is implemented in full in the chapter on neurology. This classification differentiates
between primary (idiopathic), secondary (symptomatic) headache, and orofacial pain
including cranial neuralgias. In the section on chronic pain, only chronic headache
and chronic orofacial pain will be included. Chronic headache and chronic orofacial
pain is defined as headaches or orofacial pains that occur on at least 50% of the
days during at least 3 months. For most purposes, patients receive a diagnosis according
to the headache phenotypes or orofacial pains that they currently present. The section
will list the most frequent chronic headache conditions.
The most common chronic orofacial pains are temporomandibular disorders,
which have been included in this subchapter of chronic pain. Chronic orofacial pain
can be a localized presentation of a primary headache.
This is common in the trigeminal autonomic cephalalgias, less common in migraines,
and rare in tension-type headache. Several chronic orofacial pains such as post-traumatic
trigeminal neuropathic pain,
persistent idiopathic orofacial pain, and burning mouth syndrome are cross-referenced
to, eg, primary chronic pain and neuropathic pain. The temporal definition of “chronic”
has been extrapolated from that of chronic headaches.
2.6. Chronic visceral pain
Chronic visceral pain is persistent or recurrent pain that originates from the internal
organs of the head and neck region and the thoracic, abdominal, and pelvic cavities.
The pain is usually perceived in the somatic tissues of the body wall (skin, subcutis,
muscle) in areas that receive the same sensory innervation as the internal organ at
the origin of the symptom (referred visceral pain).
In these areas, secondary hyperalgesia (increased sensitivity to painful stimuli in
areas other than the primary site of the nociceptive input) often occurs
; the intensity of the symptom may bear no relationship with the extent of the internal
damage or noxious visceral stimulation.
The section on visceral pain will be subdivided according to the major underlying
mechanisms, ie, persistent inflammation, vascular mechanisms (ischemia, thrombosis),
obstruction and distension, traction and compression, combined mechanisms (eg, obstruction
and inflammation concurrently), and referral from other locations. Pain due to cancer
will be cross-referenced to the chapter chronic cancer pain and pain due to functional
or unexplained mechanisms to chronic primary pain.
2.7. Chronic musculoskeletal pain
Chronic musculoskeletal pain is defined as persistent or recurrent pain that arises
as part of a disease process directly affecting bone(s), joint(s), muscle(s), or related
soft tissue(s). According to the constraints of the approach as described in the Introduction,
this category is therefore limited to nociceptive pain and does not include pain that
may be perceived in musculoskeletal tissues but does not arise therefrom, such as
the pain of compression neuropathy or somatic referred pain. The entities subsumed
in this approach include those characterized by persistent inflammation of infectious,
autoimmune or metabolic etiology, such as rheumatoid arthritis, and by structural
changes affecting bones, joints, tendons, or muscles, such as symptomatic osteoarthrosis.
Musculoskeletal pain of neuropathic origin will be cross-referenced to neuropathic
pain. Well-described apparent musculoskeletal conditions for which the causes are
incompletely understood, such as nonspecific back pain or chronic widespread pain,
will be included in the section on chronic primary pain.
Irrespective of its etiology, chronic pain is a major source of suffering and requires
special treatment and care. Our proposal may not represent a perfect solution for
the classification of all manifestations of chronic pain. However, it does represent
the first systematic approach to implementing a classification of chronic pain in
the ICD. It is based on international expertise and agreement, and consistent with
the requirements of the ICD regarding the structure and format of content models.
The 7 major categories of chronic pain were identified after considerable research
and discussion. They represent a compromise between comprehensiveness and practical
applicability of the classification system. Several clinically important conditions
that were neglected in former ICD revisions will now be mentioned, eg, chronic cancer
pain or chronic neuropathic pain. Etiological factors, pain intensity, and disability
related to pain will be reflected. With the introduction of chronic primary pain as
a new diagnostic entity, the classification recognizes conditions that affect a broad
group of patients with pain and would be neglected in etiologically defined categories.
We hope that this classification strengthens the representation of chronic pain conditions
in clinical practice and research and welcome comments to improve it further.
Conflict of interest statement
Q. Aziz has attended advisory board meetings for Almirall pharmaceuticals and Grunenthal.
He has also received funding for clinical trials from Ono Pharmaceutical and Protexin.
M.I. Bennett has received consultancy or speaker fees from Pfizer, Bayer, Astellas,
and Grunenthal in the last 5 years. M. Cohen has received honoraria for contributions
to educational programs from Mundipharma Pty Limited and Pfizer. S. Evers received
honoraria (as speaker and/or member of advisory boards) and research grants within
the past 5 years by AGA Medical (now St Jude), Allergan, Almirall, Astra Zeneca, Berlin-Chemie,
CoLucid, Desitin, Eisai, GlaxoSmithKline, Ipsen Pharma, Menarini, MSD, Novartis, Pfizer,
Reckitt-Benckiser, UCB. N.B. Finnerup has received speaker's honoraria from Pfizer,
Grunenthal, and Norpharma, research grant from Grünenthal, and consultancy fee from
Astellas and is member of the IMI “Europain” collaboration where industry members
of this are: Astra Zeneca, Pfizer, Esteve, UCB-Pharma, Sanofi Aventis, Grünenthal,
Eli Lilly, Boehringer Ingelheim, Astellas, Abbott, and Lundbeck. M.B. First on the
faculty of the Lundbeck International Neuroscience Foundation. In the past 2 years,
M.A. Giamberardino received research funding or honoraria (participation in Advisory
Board) from Bayer Healthcare, Helsinn, and Epitech Group. S. Kaasa declares no conflict
of interest related to this work. In the past year he received honoraria from Helsinn
related to participation in Advisory Board. E. Kosek has received consultancy and
speaker fees in the past 24 months from Eli Lilly and Company and Orion and has ongoing
research collaborations with Eli Lilly and Company and Abbott and Pierre Fabre. M.
Nicholas received honoraria for contributing to educational sessions for Mundipharma
and Pfizer in the last 5 years. S. Perrot received honoraria as a speaker and/or member
of the advisory board in the past 5 years from Pfizer, BMS, Grunenthal, Elli Lilly,
Sanofi, Daichi-Sankyo, Astellas, and Mundipharma. He has received grant support from
BMS. W. Rief received honoraria (as speaker and/or member of advisory boards on topics
such as adherence, placebo mechanisms) within the past 5 years from Berlin Chemie,
Astra Zeneca, Bayer, Heel (research grant). J. Scholz has received speaker fees from
Convergence, GlaxoSmithKline, Pfizer, St Jude Medical, and Zalicus. He has served
on advisory boards or consulted for Convergence, Pfizer, Sanofi Aventis, and Zalicus
Pharmaceuticals. He has received grant support from GlaxoSmithKline and Pfizer. In
the last 5 years, the Anaesthesiology Unit of the University of Western Australia,
but not S. Schug personally, has received research and travel funding and speaking
and consulting honoraria from bioCSL, Bionomics, Eli Lilly, Grunenthal, Janssen, Mundipharma,
Pfizer, Phosphagenics and iX Biopharma within the last 2 years. B.H. Smith has received
lecture and consultancy fees, on behalf of his institution, from Pfizer, Grunenthal,
Eli Lilly, and Napp. He has received unconditional educational grants from Pfizer
Ltd; and he has received travel and accommodation support from Napp. P. Svensson served
as a paid consultant for Sunstar Suisse SA. R.-D. Treede has received speaker's honoraria,
research grants or consultancy fees from AbbVie, Acron, Astellas, Bauerfeind, Boehringer
Ingelheim, Grünenthal, Hydra, Mundipharma, and Pfizer and is a member of the IMI “Europain”
collaboration where industry members of this are: Astra Zeneca, Pfizer, Esteve, UCB-Pharma,
Sanofi Aventis, Grünenthal, Eli Lilly, Boehringer Ingelheim, Astellas, Abbott, and
Lundbeck. J.W.S. Vlaeyen is a member of the PHILIPS advisory board on pain management
and declares no conflicts of interest with regard to this work. S.-J. Wang has served
on the advisory boards of Allergan and Eli Lilly, Taiwan. He has received speaking
honoraria from local companies (Taiwan branches) of Pfizer, Elli Lilly, and GSK. He
has received research grants from the Novartis Taiwan, Taiwan Ministry of Science
and Technology, Taipei-Veterans General Hospital and Taiwan Headache Society. The
other authors have no conflicts of interest to declare.