Definitions of Chronic Pain Syndromes
Chronic Pain [Treede et al., 2019]
Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.  Often, pain serves as a symptom warning of a medical condition or injury. In these cases, treatment of the underlying medical condition is crucial and may resolve the pain. However, pain may persist despite successful management of the condition that initially caused it, or because the underlying medical condition cannot be treated successfully.
Chronic pain is pain that persists or recurs for longer than three months. Such pain often becomes the sole or predominant clinical problem in some patients [1-3]. As such it may warrant specific diagnostic evaluation, therapy and rehabilitation. Chronic pain is a frequent condition, affecting an estimated 20% of people worldwide [4-7].
This code should be used if a pain condition persists or recurs for longer than 3 months.
 IASP Taxonomy working Group (2011) Classification of Chronic Pain (Second Edition) [Accessed 25/02/2015 https://www.iasp-pain.org/PublicationsNews/Content.aspx?ItemNumber=1673&navItemNumber=677]
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Chronic Primary Pain [Nicholas et al., 2019]
Chronic primary pain is chronic pain in one or more anatomical regions that persists or recurs for longer than 3 months, and that is characterized by significant emotional distress (anxiety, anger/frustration or depressed mood) or functional disability (interference in daily life activities and reduced participation in social roles). Chronic primary pain is multifactorial: biological psychological and social factors contribute to the pain syndrome. The diagnosis is appropriate independently of identified biological or psychological contributors unless another diagnosis would better account for the presenting symptoms. Other chronic pain diagnoses to be considered are chronic cancer-related pain, chronic postsurgical or posttraumatic pain, chronic neuropathic pain, chronic secondary headache or orofacial pain, chronic secondary visceral pain and chronic secondary musculoskeletal pain. Patients with chronic primary pain often report increased depressed  and anxious  mood, as well as anger  and frustration . In addition, the pain significantly interferes with daily life activities and participation in social roles . Chronic primary pain is a frequent condition, and treatment should be geared towards the reduction of pain-related distress and disability [e.g. 6].
Conditions A to C are fulfilled:
A. Chronic pain (persistent or recurrent for longer than 3 months) is present
B. The pain is associated with at least one of the following:
B.1 Emotional distress due to pain is present.
B.2 The pain interferes with daily life activities and social participation.
C. The pain is not better accounted for by another chronic pain condition.
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 Blyth, F. M., March, L. M., Brnabic, A. J. M., Jorm, L. R., Williamson, M., & Cousins, M. J. Chronic pain in Australia: a prevalence study. Pain 2001, 89(2,3), 127-134.
 Sullivan MJL, Adams H, Martel M-O, Scott W, Wideman T. Catastrophizing and Perceived Injustice Risk Factors for the Transition to Chronicity After Whiplash Injury. Spine 2011; 36, S244–S249
 Chou R, Loeser JD, Owens DK, et al, for the American Pain Society Low Back Pain Guideline Panel. Interventional therapies, surgery, and interdisciplinary rehabilitation for low back pain: an evidence-based clinical practice guideline from the American Pain Society. Spine 2009; 34: 1066–77.
Chronic Cancer-Related Pain [Bennett et al., 2019]
Chronic cancer-related pain is pain caused by the primary cancer itself or metastases (chronic cancer pain) or its treatment (chronic post-cancer treatment pain). It is distinct from pain caused by co-morbid disease [1-3]. It should be highly probable that the pain is due to cancer or its treatment; if its genesis is vague, consider using codes in the section of Primary pain.
On average, each cancer patient will identify two distinct pains . In many patients, careful assessment is therefore required to distinguish pain caused by cancer from pain caused by cancer treatment or co-morbid conditions. In particular, it is common for these pains to overlap, for example, thoracic surgery for a lung cancer might cause post-surgical pain, which can be exacerbated by cancer recurrence in the same area. In these situations, the clinician must decide the predominant cause of pain and base treatment on this.
Conditions A to C are fulfilled:
A. Chronic pain (persistent or recurrent for longer than 3 months) is present.
B. At least one of the following is fulfilled:
B.1 The pain is caused by an active tumor (including metastases).
B.2 The pain is caused by the cancer treatment (including but not limited to surgery, chemotherapy, radiotherapy).
C. The pain is not better accounted for by another diagnosis of chronic pain
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 Knudsen AK, Brunelli C, Klepstad P, Aass N, Apolone G, Corli O, Montanari M, Caraceni A, Kaasa S. Which domains should be included in a cancer pain classification system? Analyses of longitudinal data. Pain. 2012 Mar;153(3):696-703
Chronic Postsurgical or Posttraumatic Pain [Schug et al., 2019]
Chronic postsurgical or posttraumatic pain is pain developing or increasing in intensity after a surgical procedure or a tissue injury (involving any trauma including burns) and persisting beyond the healing process, i.e. at least 3 months after surgery or tissue trauma. The pain is either localized to the surgical field or area of injury, projected to the innervation territory of a nerve situated in this area, or referred to a dermatome (after surgery/injury to deep somatic or visceral tissues). Other causes of pain including infection, malignancy etc. need to be excluded as well pain as continuing from a pre-existing pain problem. The postsurgical or posttraumatic etiology of the pain should be highly probable; if it is vague, consider using codes in the section of chronic primary pain.
The most frequent surgical procedures causing chronic post-surgical pain are breast surgery (including mastectomy with or without axillary node dissection, cosmetic surgery), herniotomy (open or laparoscopic surgery), thoracic surgery (including minimally invasive procedures like thoracoscopic surgery) and the amputation of a limb or other organ. Dependent on the type of surgery, chronic postsurgical pain often may be neuropathic pain; on average chronic postsurgical pain is in 30% of cases of neuropathic origin (range 6 to 54% and more).
Chronic pain can also develop after trauma; the incidence is reported in the range of 46 to 85% after multitrauma. Typical examples include posttraumatic osteoarthritis after joint injuries, chronic pain after acute back injury, whiplash injury and burns injury.
Even if neuropathic mechanisms are crucial, this type of pain should be diagnosed here.
Condition A – D have to be fulfilled:
A. Pain that began after surgery or a tissue trauma is experienced.
B. The pain is in an area of preceding surgery or tissue trauma.
C. The pain persisted for at least three months after the initiating event.
D. The pain is not better explained by an infection, a malignancy, a pre-existing pain condition or any other alternative cause.
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Chronic Neuropathic Pain [Scholz et al., 2019]
Chronic neuropathic pain is chronic pain caused by a lesion or disease of the somatosensory nervous system . The somatosensory nervous system provides information about the body including skin, musculoskeletal and visceral organs. A lesion or disease causing neuropathic pain may involve peripheral or central structures of the somatosensory nervous system. Persistence or recurrence over ≥ 3 months defines chronic pain (see 6 Temporal Properties). The pain may be spontaneous (continuous or episodic) 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, a stroke or nerve trauma, or disease, for example, diabetic neuropathy, and a neuroanatomically plausible distribution of the pain . Negative (for example, decreased or loss of sensation) and positive sensory symptoms or signs (for example, allodynia or hyperalgesia) must be compatible with the innervation territory of the affected nervous structure. Demonstration of the lesion or disease involving the nervous system, for example, by imaging techniques neurophysiological or laboratory tests, confirms the diagnosis of definite neuropathic pain .
Neuropathic pain is a major source of physical impairment, emotional and psychosocial distress , and requires multimodal treatment with a specific pharmacological component [4, 5].
For the diagnosis of chronic neuropathic pain, pain must persist or recur for ≥ 3 months and fulfill at least criteria A and D below. Criteria B and C increase the level of diagnostic certainty.
A. The pain is characterized by both of the following:
A.1 History of relevant neurological lesion or disease
A.2 Pain distribution neuroanatomically plausible
B. Pain is associated with sensory signs in the same neuroanatomically plausible distribution
C. Diagnostic test confirming a lesion or disease of the somatosensory nervous system explaining the pain
D. Not better accounted for by another diagnosis of chronic pain.
Negative or positive sensory signs consistent with the distribution of the pain may be sufficient to indicate the presence of a lesion or disease of the somatosensory nervous system. The clinical examination may be supplemented by laboratory tests, for example, quantitative sensory testing.
Tests that reveal a relevant lesion or disease affecting the somatosensory system may, for example, consist of magnetic resonance imaging (MRI) or computed tomography (CT) confirmation of a stroke or multiple sclerosis, surgical or radiological confirmation of nerve compression, nerve conduction study, laser-evoked potentials, blink reflex, or skin biopsy confirmation of reduced nerve fiber terminals. Positive findings in these investigations may provide important diagnostic hints at the source of pain. However, all clinical and diagnostic aspects of the pain need to be considered before assuming causality.
 International Association for the Study of Pain (IASP) (http://www.iasp-pain.org/Taxonomy)
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Chronic Secondary Headache or Orofacial Pain [Benoliel et al., 2019]
Chronic secondary headache or orofacial pain comprises all headache and orofacial pain disorders that have underlying causes and occur on at least 50% of the days during at least three months. The duration of pain per day is at least 2 hours per day. If the etiology is vague, consider using codes in the section of chronic primary pain.
For most purposes, patients receive a diagnosis according to the underlying causes, and some secondary headache and orofacial pain disorders present with typical headache and orofacial pain phenotypes. It can be difficult to separate between primary and secondary headache in some cases (e.g., chronic migraine with medication overuse).
Each distinct type, subtype, or subform of headache or orofacial pain that the patient has 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.
To receive a particular chronic secondary headache or orofacial pain diagnosis the patient must, in many cases, experience a minimum number of attacks of (or days with) that headache or orofacial pain. This number is specified in the explicit diagnostic criteria for each headache type or type of orofacial pain. Further, the headache or orofacial pain must fulfill a number of further requirements for each specific subtype.
For chronic secondary orofacial pain conditions, some of the disorders may be listed under musculoskeletal diseases or diseases of the digestive system.
Conditions A to D are fulfilled:
A. Headache or orofacial pain for >2 hours on ≥15 days per month for longer than 3 months.
B. Another disorder scientifically documented to be able to cause headache or orofacial pain has been diagnosed.
C. Evidence of causation demonstrated by at least two of the following:
C.1 Headache or orofacial pain has developed in temporal relation to the onset of the presumed causative disorder
C.2 One or both of the following is fulfilled:
a) Headache or orofacial pain has significantly worsened in parallel with worsening of the presumed causative disorder
b) Headache or orofacial pain has significantly improved in parallel with improvement of the presumed causative disorder
C.3 Headache or orofacial pain has characteristics typical for the causative disorder
C.4. Other evidence exists of causation
D. The pain is not better accounted for by another diagnosis.
 Headache Classification Committee of the International Headache Society. The International Classification of Headache Disorders, 3rd edition (beta). Cephalalgia 2013; 33: 629-808.
Chronic Secondary Visceral Pain [Aziz et al., 2019]
Chronic secondary visceral pain is persistent or recurrent pain originating from internal organs of the head/neck region and of the thoracic, abdominal and pelvic cavities [3,4,6,7]. The visceral etiology of the pain should be highly probable; if it is vague, consider using codes in the section of chronic primary pain. The pain is 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/noxious visceral stimulation .
Conditions A to D are fulfilled:
A. Chronic pain (persistent or recurrent for longer than 3 months) is present and characterized by both of the following:
A.1 The distinct anatomical location is compatible with typical referral pain patterns from specific internal organs.
A.2 The history is suggestive of relevant dysfunction/disease of one or more internal organs.
B. At least one confirmatory test demonstrates an anatomical location compatible with a specific referred pain pattern.
C. At least one confirmatory test demonstrates the relevant dysfunction/disease.
D. The pain is not better accounted for by another diagnosis of chronic pain.
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Chronic Secondary Musculoskeletal Pain [Perrot et al., 2019]
Chronic secondary musculoskeletal pain is chronic pain arising from bone(s), joint(s), muscle(s), vertebral column, tendon(s)or related soft tissue(s). It is a heterogeneous group of chronic pain conditions originating in persistent nociception in joint, bone, muscle, vertebral column, tendon and related soft tissues, with local and systemic etiologies, but also related to deep somatic lesions. If the pain is related to visceral lesions, it should be considered whether a diagnosis of chronic visceral pain is appropriate; if it is related to neuropathic mechanisms, it should be coded under chronic neuropathic pain; and if the pain mechanisms are non-specific, chronic musculoskeletal pain should be coded under chronic primary pain.
Chronic secondary musculoskeletal pain can be characterized either by persistent local or systemic inflammatory illness, which may be due to infectious diseases, crystal deposition or auto-immune processes, or attributable to structural changes.
Other biomedical causes responsible for musculoskeletal pain may also apply (such as neurologically caused muscle spasms and referred pain from deep tissues).
The musculoskeletal origin of the pain (that is, nociception in musculoskeletal tissues) should be highly probable.
If the musculoskeletal origin does not appear highly plausible and no neuropathic origin is ascertainable; consider using codes in the section of chronic primary pain.
Conditions A to C are fulfilled:
A. Chronic pain (persistent or recurrent for longer than 3 months) in joint(s), bone(s), muscle(s), vertebral column, tendon(s) or related soft tissue is present. The pain may be spontaneous or movement induced.
B. At least one of B1 to B3 is fulfilled:
B.1 A musculoskeletal disease with inflammation due to infection, auto-immunity, auto-inflammation or metabolic disorders (crystals) is present (demonstrated by appropriate tests ) and causes the local activation of nociceptors.
B.2 A musculoskeletal disease with structural / biomechanical factors (demonstrated by appropriate tests) is present and causes the local activation of nociceptors.
B.3 A neurological disease (classified elsewhere) is present and causes altered biomechanical function that is responsible for the activation of nociceptors.
C. The pain is not better accounted for by another diagnosis of chronic pain.
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Chronic Pain Specifiers [Treede et al., 2019]
Chronic pain severity
Severity of chronic pain is determined by pain intensity, pain-related distress and interference of the pain with daily activities and participation.
Pain intensity may be assessed verbally or on a numerical or visual rating scale. For the severity coding the patient should be asked to rate the average pain intensity for the last week on an 11-point NRS rating scale (ranging from from 0 ‘no pain’ to 10 ‘worst pain imaginable’) or a 100 mm VAS scale:
Pain-related distress is the multifactorial unpleasant emotional experience of a psychological (cognitive, behavioral, emotional), social or spiritual nature due to the persistent or recurrent experience of pain. It may be assessed by asking the person to rate the pain-related distress they experienced in the last week on an 11-point numerical rating scale or a VAS scale from ‘no pain-related distress’ to ‘extreme pain-related distress’ (‘Distress Thermometer’).
The average pain-related interference last week as rated by the patient on an 11-point numerical rating scale (NRS: from 0 ‘no interference’ to 10 ‘unable to carry on activities’) or Visual Analog Scale (VAS: 0mm ‘no interference’ to 100mm ‘unable to carry on activities’).
Overall severity combines the ratings of intensity, distress and disability using a three-digit code: Example: A patient with a moderate pain intensity, severe distress and mild disability will receive the code ‘231’. The severity code is optional.
Chronic pain is commonly defined as pain persisting for more than 3 months. It can be continuously ongoing or recurrent in nature. Additionally pain attacks may be present.
Presence of Psychosocial Factors
Psychosocial factors which contribute to the onset, the maintenance or exacerbations of pain or are a consequence of pain can be cognitive (e.g. catastrophizing, fear avoidance beliefs, worry/rumination, hypervigilance), behavioral (e.g. avoidance or endurance behavior, dysfunctional operant processes), emotional (e.g. fear of pain, injuries or illness progression, specific and general health fears, hopelessness/demoralization) or social (e.g. job strain, socioeconomic hardship, lack of social support).
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