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The definition of Pain

Pain is subjective and, as such, finding a comprehensive definition of pain can be a challenge. The most widely accepted definition of pain was derived by a taxonomy task force of the International Association of the study of pain and states that “Pain is an unpleasant sensory and emotional experience that is associated with actual or potential tissue damage or described in such terms.”. Due to its subjectivity, health professionals must rely on the patient’s own description of the type, onset, duration and location of pain during evaluation.

With that said, acute pain is often believed to be directly associated with tissue injury/damage, is usually transitory, and lasts only until the noxious stimulus is removed or the underlying damage/pathology has healed. The intensity and location of the pain are often considered to be an accurate reflection of the tissue problem. Acute pain is relatively short in duration, often resolves on its own, and can be treated effectively with primary care.

Acute pain is:

  • an adaptive response of an organism’s protective system;

  • a type of pain which motivates an individual to consciously perform protective actions to promote healing and recovery; and

  • a type of pain which triggers automatic responses to promote recovery.

Chronic pain is typically defined as pain which lasts more than three to six months, or “beyond the point of tissue healing”. Unlike acute pain, intensity and location of pain are considered inaccurate representations of tissue injury. [1]

Chronic pain can also be described as:

  • a maladaptive response of an organism’s protective system;

  • a type of pain which motivates an individual to consciously perform protective actions that limit recovery; and

  • a type of pain which triggers automatic responses that limit recovery.

This type of pain response no longer provides a protective purpose or positive adaptation, and puts the body (and mind) in a high state of stress. The pain system becomes hypersensitive (central sensitization) which not only limits recovery and prolongs/intensifies pain but may also induce additional negative physiological (and psychological) effects.

“It has become clear that the majority of cases of chronic musculoskeletal pain are characterized by alterations in central nervous system processing. More specifically, the responsiveness of central neurons to input from unimodal and polymodal receptors is augmented, resulting in a pathophysiological state corresponding to central sensitization, characterized by generalized or widespread hypersensitivity.” [2]

“Central sensitization is a condition of the nervous system that is associated with development and maintenance of chronic pain. When central sensitization occurs, the nervous system goes through a process called wind-up and gets regulated in a persistent state of high reactivity. This persistent, or regulated, state of reactivity lowers the threshold for what causes pain and subsequently comes to maintain pain even after the initial injury may have healed.” [3]

Based on the evolution of our understanding of pain, it has become apparent that chronic pain is not a singular entity but rather has a multitude of causes and presentations.

References:

[1] Acute versus Chronic Pain: Understanding the difference and choosing appropriate treatment. Neil Pearson - 2012

[2] R.A. Meyer, J.N. Cambel, S.N. Raja - Peripheral neural mechanisms of nociception - 1995

[3] Institute for Chronic Pain - What is Central Sensitization

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