Musculoskeletal Pain Mechanisms: Quick Guide to Classifying Pain

Pain is hard, confusing, and sometimes elusive. There are many different types of pain and mechanisms of how they occur. Each has a very specific set of signs and symptoms that can make it fairly predictable and identifiable. Once there is a good grasp on the type of pain that you may be dealing with, there can be a specific treatment plan made accordingly. The goal of classification is to consistently recognize certain patterns and increase the utility and effectiveness of clinical care. There are numerous pain generators but most musculoskeletal will likely fall into a few main groups. Musculoskeletal pain mechanisms can generally be classified into 3 main types: Nociceptive Pain, Peripheral Neuropathic pain (PNP), and Central Sensitization Pain (CSP).

Nociceptive pain is defined as a perception of threat induced by activation of peripheral receptive terminals of primary afferent neurons in response to a noxious chemical (inflammation), mechanical stimuli or thermal stimuli (Smart et al., 2010).

A regression analysis performed by Smart et al. (2012) identified a cluster of clinical criteria predictive of NP, including:

  1. Pain localized to the area of injury/dysfunction
    • Strongest predictor of NP
    • If positive you are 69x  more likely to have NP
  2. Clear, proportionate mechanical/anatomical nature to aggravating and easing factors
  3. Usually intermittent and sharp with movement/mechanical provocation and more of a constant, dull ache or throb at rest
  4. Absence of
    • Pain associated with other dysesthesias
      • Presence of dyesthesias decreased the odds of being classified with NP by 85%
    • Night pain/disturbed sleep
    • Antalgic postures/movement patterns
    • Pain described as burning, shooting, sharp or electric-shock-like

This cluster was found to have high levels of classification accuracy with a sensitivity of 90.9% and specificity of 91.0%.

Peripheral neuropathic pain (PNP) is pain arising from a primary lesion or dysfunction in the peripheral nervous system. Smart et al. found three criteria to be predictive of PNP.

  1. Pain referred in a dermatomal or cutaneous distribution
    • Strongest predictor of PNP
    • > 24x more likely to be classified as PNP dominance
  2. History of nerve injury, pathology or mechanical compromise
    • 12x more likely to be classified as PNP dominance
  3. Pain/symptom provocation with mechanical/movement tests that move/load/compress neural tissue
    • Neurodynamic testing
    • 14x more likely to be classified as PNP dominance

This cluster was found to have high levels of classification accuracy with a sensitivity of 86.3% and a specificity of 96.0%.

Central Sensitization Pain (CSP) refers to pain arising from a dominance of neurophysiological dysfunction within the central nervous system. CSP dominance was predicted by the presence of 3 symptoms and 1 sign.

  1. Disproportionate, non-mechanical, unpredictable pattern of pain provocation in response to multiple/nonspecific aggravating/easing factors
    • >30x more likely to be classified with a dominance of CSP
  2. Pain disproportionate to the nature and extent of injury or pathology
  3. Strong association with maladaptive psychosocial factors/yellow flags (e.g. negative emotions, poor self-efficacy, maladaptive beliefs and pain behavior)
  4. Diffuse/non-anatomic areas of pain/tenderness on palpation

This cluster was found to have high levels of classification accuracy with a sensitivity of 91.8% and a specificity of 97.7%. Patients who demonstrate a majority of this cluster are over 40x more likely to have CSP than non-CSP.

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