Chronic pain is defined as reoccurring or persistent pain lasting more than 3 months. The International Association for the Study of Pain (IASP) defines pain as "An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage". Chronic pain continues past normal healing times and therefore does not have the same function as acute pain, which is to signal that there is a threat so the body can avoid future danger. Chronic pain is considered a syndrome because of the associated symptoms that develop in those experiencing this disorder. Chronic pain affects approximately 20% of people worldwide and accounts for 15–20% of visits to a physician. Pain can be categorized according to its location, cause, or the anatomical system which it affects. Pain can also defy these classifications, making it difficult to classify chronic pain. The newest standard for classifying chronic pain was created for the ICD-11. To create this classification system the IASP collaborated with the World Health Organization to form the Task Force for the Classification of Chronic Pain. The IASP Task Force was made up of pain experts. This task force developed a new model to classify chronic pain for the ICD-11. This new classification system emphasizes the cause of pain, underlying mechanisms, body sites, and the biopsychosocial model of chronic pain. This classification system differentiates chronic primary pain from chronic secondary pain, incorporates already existing diagnosis, and further characterizes chronic pain syndromes. The ICD-11 category for chronic pain includes the most common types of chronic pain, chronic primary pain, chronic cancer pain, chronic posttraumatic and postsurgical pain, chronic neuropathic pain, chronic secondary headache and orofacial pain, chronic secondary visceral pain, and chronic secondary musculoskeletal pain. There can also be significant overlap between the categories. The ICD-11 also has an "other" subcategory for each category of pain, such as "other specified chronic cancer pain" or "other specified chronic neuropathic pain", to include chronic pain that does not fit into other categories.
Chronic primary pain Chronic primary pain affects one or more anatomical sites, reoccurs or persists for more than three months, causes emotional distress or functional disability, and cannot be better explained by another chronic pain condition. Emotional distress can be expressed in a number of ways such as frustration, anxiety, depression, demoralization, and anger. Functional disability encompasses a large range of difficulties such as working, sleeping, or social activities. Chronic primary pain can affect any body system or site and can also be widespread. Conditions within this category are further classified into chronic widespread pain, complex regional pain syndromes, chronic primary headache and orofacial pain, chronic primary visceral pain, and chronic primary musculoskeletal pain.
Chronic widespread pain Chronic widespread pain is defined as diffuse musculoskeletal pain affecting at least four of five body regions and in at least three or more body quadrants and axial skeleton. Body quadrants are defined as the upper left, upper right, lower left, and lower right quadrants of the body. Chronic widespread pain cannot be attributed to a nociceptive process in these areas.
Fibromyalgia Myofascial pain syndrome
Complex regional pain syndromes
Complex regional pain syndrome is characterized by pain that is distributed regionally, usually starts in an extremity distally, occurs after a trauma, and is disproportionate in severity or duration compared to the expected course of the trauma — the sites affected by complex regional pain syndrome experience autonomic and inflammatory changes. Complex regional pain syndrome is divided into two types, type 2 requires evidence of peripheral nerve injury, while type 1 does not.
Complex regional pain syndrome type I Complex regional pain syndrome type II
Chronic primary headache and orofacial pain Chronic primary headache or orofacial pain is orofacial pain or headache that persists for longer than three months and occurs at least 15 days a month. When untreated the pain lasts at least two hours or can occur as many shorter episodes of pain throughout the day.
Chronic migraine Chronic tension-type headache Trigeminal autonomic cephalalgias Chronic temporomandibular disorder Chronic burning mouth pain Chronic primary orofacial pain
Chronic primary visceral pain
Chronic primary visceral pain occurs in the head or neck viscera of the digestive system; the abdominal area from viscera of the digestive system, such as IBS; the thoracic region, such as non-cardiac chest pain; and the pelvic area from the involvement of viscera of the urinary, digestive, and genital systems, such as chronic pelvic pain. Visceral pain is caused by nociceptor activation in pelvic, thoracic, or abdominal organs.
Chronic primary chest pain syndrome Chronic primary epigastric pain syndrome Irritable bowel syndrome Chronic primary abdominal pain syndrome Chronic primary bladder pain syndrome Chronic primary pelvic pain syndrome
Chronic primary musculoskeletal pain Chronic primary musculoskeletal pain affects the joints, muscles, bones, or tendons. Chronic primary musculoskeletal pain syndromes are classified by the location in which they affect.
Chronic primary low back pain Chronic primary cervical pain Chronic primary thoracic pain Chronic primary limb pain
Chronic secondary pain Chronic secondary pain syndromes are caused by other medical conditions. Pain may initially be a symptom of a disease, however, it can also persist after successful treatment of the underlying disorder. Chronic secondary pain can be further categorized into 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.
Chronic cancer-related pain
Pain is the most common symptom of cancer at the time of diagnosis. Cancer-related pain can be caused by metastases, the tumour itself, inflamed or eroding bone viscera or nerves, or pain related to cancer treatments. The term "cancer-related pain" only indicates that pain is related to cancer and does not imply the exact cause of the pain.
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