Classification of Pain

Classification of pain: Classifying pain is helpful to guide assessment and treatment. There are many ways to classify pain and classifications may overlap (Table 1). The common types of pain include:

  • Nociceptive: represents the normal response to noxious insult or injury of tissues such as skin, muscles, visceral organs, joints, tendons, or bones.
    • Examples include:
      • Somatic: musculoskeletal (joint pain, myofascial pain), cutaneous; often well localized
      • Visceral: hollow organs and smooth muscle; usually referred
  • Neuropathic: pain initiated or caused by a primary lesion or disease in the somatosensory nervous system.
    • Sensory abnormalities range from deficits perceived as numbness to hypersensitivity (hyperalgesia or allodynia), and to paresthesias such as tingling.
    • Examples include, but are not limited to, diabetic neuropathy, postherpetic neuralgia, spinal cord injury pain, phantom limb (post-amputation) pain, and post-stroke central pain.
  • Inflammatory: a result of activation and sensitization of the nociceptive pain pathway by a variety of mediators released at a site of tissue inflammation.
    • The mediators that have been implicated as key players are proinflammatory cytokines such IL-1-alpha, IL-1-beta, IL-6 and TNF-alpha, chemokines, reactive oxygen species, vasoactive amines, lipids, ATP, acid, and other factors released by infiltrating leukocytes, vascular endothelial cells, or tissue resident mast cells
    • Examples include appendicitis, rheumatoid arthritis, inflammatory bowel disease, and herpes zoster.

Clinical Implications of classification: Pathological processes never occur in isolation and consequently more than one mechanism may be present and more than one type of pain may be detected in a single patient; for example, it is known that inflammatory mechanisms are involved in neuropathic pain.

  • There are well-recognized pain disorders that are not easily classifiable. Our understanding of their underlying mechanisms is still rudimentary though specific therapies for those disorders are well known; they include cancer pain, migraine and other primary headaches and wide-spread pain of the fibromyalgia type.

Pain Intensity: Can be broadly categorized as: mild, moderate and severe. It is common to use a numeric scale to rate pain intensity where 0 = no pain and 10 is the worst pain imaginable:

  • Mild: <4/10
  • Moderate: 5/10 to 6/10
  • Severe: >7/10

Time course: Pain duration

  • Acute pain: pain of less than 3 to 6 months duration
  • Chronic pain: pain lasting for more than 3-6 months, or persisting beyond the course of an acute disease, or after tissue healing is complete.
  • Acute-on-chronic pain: acute pain flare superimposed on underlying chronic pain.