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 http://www.iasp-pain.org/PublicationsNews/Content.aspx?ItemNumber=1673&navItemNumber=677]
 Bonica JJ. (1953) The Management of Pain: With Special Emphasis on the Use of Analgesic Block in Diagnosis, Prognosis and Therapy. Philadelphia: Lea & Febiger.
 Treede RD (2013) Entstehung der Schmerzchronifizierung. In: Baron R, Koppert W, Strumpf M, Willweber-Strumpf A (Eds), Praktische Schmerztherapie, 3. Edition, Heidelberg: Springer pp. 3-13
 Breivik H, Collett B, Ventafridda V, Cohen R, Gallacher D. (2006) Survey of Chronic Pain in Europe: Prevalence, Impact on Daily Life, and Treatment. European Journal of Pain 10: 287–287.
 Goldberg DS, Summer JM (2011) Pain as a global public health priority. BMC Public Health 11:770.
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Chronic Primary Pain
Chronic primary pain is chronic pain in one or more anatomical regions that is characterized by significant emotional distress (anxiety, anger/frustration or depressed mood) and 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 pain, chronic postsurgical or posttraumatic pain, chronic neuropathic pain, chronic headache or orofacial pain, chronic visceral pain and chronic 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].
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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 Pain
Chronic cancer pain is pain caused by the cancer itself (primary tumor and metastases) or its treatment. It is distinct from pain caused by co-morbid disease [1-3]. 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. It should be highly probable that the pain is due to cancer; if its genesis is vague, consider using codes in the section of Primary pain.
 Bennett MI, Rayment C, Hjermstad M, Aass N, Caraceni A, Kaasa S. Prevalence and aetiology of neuropathic pain in cancer patients: a systematic review. Pain. 2012 Feb;153(2):359-65.
 Caraceni A, Portenoy RK. An international survey of cancer pain characteristics and syndromes. IASP Task Force on Cancer Pain. International Association for the Study of Pain. Pain. 1999 Sep;82(3):263-74.
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Chronic Postsurgical and Posttraumatic Pain
Chronic postsurgical and posttraumatic pain is pain developing 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. 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 genesis of the pain should be highly probable; if it is vague, consider using codes in the section of 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.
 Macrae WA. Chronic post-surgical pain: 10 years on. Br J Anaesth. 2008; 101(1):77-86.
 Schug S, Pogatzki-Zahn E. Chronic pain after surgery or injury. IASP, Pain Clinical Updates 2011; vol XIX, Issue 1.
 Haroutiunian S, Nikolajsen L, Finnerup NB, Jensen TS. The neuropathic component in persistent postsurgical pain: a systematic literature review. Pain. 2013; 154(1):95-102.
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 Castillo RC, MacKenzie EJ, Wegener ST, Bosse MJ. Prevalence of chronic pain seven years following limb threatening lower extremity trauma. Pain 2006;124:321-329.
 Browne AL, Andrews R, Schug SA, Wood F. Persistent pain outcomes and patient satisfaction with pain management after burn injury. Clin J Pain. 2011; 27(2): 136-45.
Chronic Neuropathic Pain
Chronic neuropathic pain is 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. The lesion or disease causing the pain may involve peripheral or central nervous structures. Neuropathic pain is usually chronic (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, by a stroke, nerve trauma or diabetic neuropathy, and a neuroanatomically plausible distribution of the pain . Demonstration of a lesion or disease involving the nervous system, for example, by imaging techniques, biopsy, neurophysiological or laboratory tests, is necessary for the identification of definite neuropathic pain . Negative or positive signs compatible with the innervation territory of the affected nervous structure must be present for the identification of definite neuropathic pain. The neuropathic genesis of the pain should be highly probable; if it is vague, consider using codes in the section of Primary pain.
Neuropathic pain is a major source of physical impairment, emotional and psychosocial distress after nervous system injury , and requires multimodal treatment with a specific pharmacological component [5, 6].
 International Organization for the Study of Pain (IASP) (http://www.iasp-pain.org/Education/Content.aspx?ItemNumber=1698&navItemNumber=576)
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Chronic Headache and Chronic Orofacial Pain
Chronic headache is defined as a headache occurring on at least 50% of the days during at least 3 months. This criterion can also apply to chronic orofacial pain conditions. For most purposes, patients receive a diagnosis according to the headache phenotypes that they currently present, or that they have presented within the last year. 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 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 headache diagnosis the patient must, in many cases, experience a minimum number of attacks of (or days with) that headache. This number is specified in the explicit diagnostic criteria for each headache type. Further, the headache must fulfill a number of further requirements for each specific subtype.
All chronic headache disorders can also be found in the chapter “Diseases of the nervous system”. If the headache disorder is the primary diagnosis of the patient, the code of the neurological chapter should be used. Otherwise, both codes can be used. For chronic orofacial pain conditions, some of the disorders may be listed under musculoskeletal diseases or diseases of the digestive system.
 Headache Classification Committee of the International Headache Society. The International Classification of Headache Disorders, 3rd edition (beta). Cephalalgia 2013; 33: 629-808.
Chronic Visceral Pain
Chronic 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 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 visceral genesis of the pain should be highly probable; if it is vague, consider using codes in the section of Primary Pain. The intensity of the symptom may bear no relationship with the extent of the internal damage/noxious visceral stimulation .
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Chronic Musculoskeletal Pain
Chronic musculoskeletal pain is chronic pain which arises from a disease process affecting bone(s), joint(s), muscle(s), spine or related soft tissue(s). This can be typically characterized either by persistent local or systemic inflammation, which may be due to infectious 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.
Chronic musculoskeletal pain considered to be of neuropathic origin should be coded under neuropathic pain and non-specific musculoskeletal pain under primary pain.
If the musculoskeletal origin does not appear highly plausible and no neuropathic origin is ascertainable; consider using codes in the section of primary pain.