Chronic pain has several different meanings in medicine. Traditionally, the distinction between acute and chronic pain has relied upon an arbitrary interval of time from onset; the two most commonly used markers being 3 months and 6 months since the initiation of pain, though some theorists and researchers have placed the transition from acute to chronic pain at 12 months. Others apply acute to pain that lasts less than 30 days, chronic to pain of more than six months duration, and subacute to pain that lasts from one to six months. A popular alternative definition of chronic pain, involving no arbitrarily fixed durations is "pain that extends beyond the expected period of healing."
Pain may arise from injury or disease to visceral, somatic and neural structures in the body. More broadly pain is described as malignant or non-malignant in origin.
Under persistent activation nociceptive transmission to the dorsal horn may induce a wind up phenomenon. This induces pathological changes that lower the threshold for pain signals to be transmitted. In addition it may generate nonnociceptive nerve fibers to respond to pain signals. Nonnociceptive nerve fibers may also be able to generate and transmit pain signals. In chronic pain this process is difficult to reverse or eradicate once established.
Nociceptors convey information regarding damage or trauma from the body to the central nervous system, a process called nociception, where it is interpreted by the brain as pain. Nociception occurs in any tissue or organ in which pain signals arise secondary to a disease process or trauma. If the pain occurs due to dysfunction or damage to nerves themselves, it is called neuropathic pain.
Pain may be a response to injury or any number of disease states that provoke nociception. Advances in imaging studies and electrophysiological studies allow us to gain a deeper insight into the characteristics and properties associated with the phenomenon of chronic pain.
Some chronic pain may be psychosomatic. Indicators include diffuse, difficult to describe symptoms, especially if they moved around the body and have no obvious verifiable physical cause. Having unexplained pain in three or more body parts is especially indicative.
Complete and sustained remission of many neuropathies and most idiopathic chronic pain (pain that extends beyond the expected period of healing, or chronic pain that has no known underlying pathology) is rarely achieved, but much can be done to reduce suffering and improve quality of life.
Pain management (also called pain medicine) is that branch of medicine employing an interdisciplinary approach to the relief of pain and improvement in the quality of life of those living with pain. The typical pain management team includes medical practitioners, clinical psychologists, physiotherapists, occupational therapists, and nurse practitioners. Acute pain usually resolves with the efforts of one practitioner; however, the management of chronic pain frequently requires the coordinated efforts of the treatment team.
While narcotics are often used in the management of chronic pain, high doses are associated with an increased risk of opioid overdose.
Chronic pain may cause other symptoms or conditions, including depression and anxiety. It may also contribute to decreased physical activity given the apprehension of exacerbating pain. Very little work has been done on the cognitive effects of chronic pain, with most of the publications focussing on the effects of cognition on pain but only 5% examining the effects of pain on cognition.
Chronic pain impairs the ability to direct attention, in particular when compared to controls with low intensity or no chronic pain, people with high-intensity chronic pain have significantly reduced ability to perform attention-demanding tasks. The pain sensations appear to strongly capture the attention of people with chronic pain; tests assessing the ability to attend show poorer performance than peers who do not experience chronic pain on all tests demanding attention. The exception is found with tasks that are highly demanding of attention, where performance between the two groups is equivalent. In experimental testing, two-thirds of individuals with chronic pain demonstrate clinically significant impairment of attention, independent of age, education, medication and sleep disruption. Individuals with the highest levels of pain showed greatest disruption of memory traces, suggesting that pain diminishes working memory.