Predicting transition to chronic pain

Abstract

Purpose of review Most individuals who develop pain following an inciting event will return to a healthy state as the injury heals. However, a small percentage continue to suffer, that is, transition to chronic pain. Chronic pain may persist for years and is accompanied by cognitive abnormalities, as well as diminished quality of life. In animals, persistent pain is characterized by peripheral and spinal cord reorganization, and recent evidence in humans also indicates cortical reorganization. Yet, despite more than 30 years of research, there is little agreement on the neural mechanisms that mediate the transition from acute to chronic pain. Recent findings In a longitudinal brain-imaging study, individuals who developed an intense back pain episode were followed over a 1-year period, during which pain and brain parameters were collected repeatedly. A smaller number of healthy individuals and chronic back pain patients were also studied concomitantly, as positive and negative controls. At the time of entry into the study, strength of synchrony between the medial prefrontal cortex and nucleus accumbens (i.e. functional connectivity) was predictive (>80% accuracy) of individuals who subsequently transition to chronicity 1 year later. Summary Properties of the brain’s emotional learning circuitry predict the transition to chronic pain. The involvement of this circuitry in pain remains mostly unexplored. Future human and animal model studies are necessary to unravel underlying mechanisms driving pain chronicity, with the potential of advancing novel therapeutics for preventing pain chronification.

Morphine paradoxically prolongs neuropathic pain in rats by amplifying spinal NLRP3 inflammasome activation

“…In summary, the mechanisms underlying the transition from acute to chronic pain are poorly understood (17,72,73). We discovered that a short course of morphine administered upon expression of neuropathic pain remarkably doubled the duration of CCI-allodynia.…”

Brain imaging tests for chronic pain: medical, legal and ethical issues and recommendations

“…The data can be used to measure functional brain connectivity that relates to a combination of spontaneous thought processes and ongoing neural and physiological maintenance processes; in chronic pain, these processes include those involved in ongoing pain 50 . Moreover, vari ability in brain activity can provide insight into brain health, pain sensitivity and the capacity for brain plasticity 99 ; these measures can differ between patients and healthy individuals, or vary in relation to characteristics of pain and risk factors for pain or its chronification 26,31,[100][101][102][103] , so can be clinically useful. A challenge in this approach is that the nature of any particular change in the pattern of resting-state connectivity associated with pain has not been determined, as patterns are altered in a range of clinical conditions; this uncertainty makes it unclear whether any particular pattern is related to pain itself, spontaneous thought, or other related processes.…”

Reward and motivation in pain and pain relief

“…Cellular adaptations (for example, priming and sensitization mechanisms) of the nervous system can amplify nociceptive signaling and likely contribute to pain chronicity 12 . Mechanisms of amplification have been primarily characterized in peripheral nociceptors and in the spinal cord 12 but increasingly are being studied in the brain 13 . Notably, chronic pain conditions are often accompanied by comorbid affective, emotional and cognitive disorders (for example, anxiety, depression, sleep disturbance, cognitive deficits 14 ).…”