Pain taxonomy: nociceptive, neuropathic and nociplastic pain

Classify pain by mechanism. Tissue damage activating nociceptors is nociceptive; a lesion or disease of the somatosensory system is neuropathic; altered nociception without either is nociplastic. Precise IASP terms for evoked pain are classic exam material.

1. Nociceptive pain needs actual or threatened tissue damage. It arises from activation of peripheral nociceptors in non-neural tissue, as in arthritis or a fracture. The somatosensory nervous system itself is functioning normally, which distinguishes it from neuropathic pain ¹.
2. Neuropathic pain needs a lesion or disease. IASP defines it as pain caused by a lesion or disease of the somatosensory nervous system. A demonstrable nerve disease, such as a length-dependent diabetic polyneuropathy with sensory loss, qualifies ¹.
3. Nociplastic pain is the third descriptor. It arises from altered nociception without clear tissue damage activating nociceptors and without a somatosensory lesion; augmented central processing is the proposed mechanism, and fibromyalgia is the prototype ²¹.
4. Clinical criteria grade nociplastic pain. Proposed criteria require chronic regional or widespread pain with evoked pain hypersensitivity; comorbidities such as sleep disturbance, fatigue, cognitive problems or sensory hypersensitivity strengthen it to "probable" ³².
5. Know the evoked-pain vocabulary. Allodynia is pain from a stimulus that does not normally provoke pain; hyperalgesia is increased pain from a normally painful stimulus; hyperpathia is an abnormally painful, often explosive reaction, especially to repetitive stimuli ¹.
6. Visceral pain is diffuse and referred. Sparse visceral afferents converge with somatic afferents on shared spinal neurons, so visceral pain is poorly localized and felt in somatic areas of the same segments ⁴.

A demonstrated somatosensory lesion or disease makes pain neuropathic; call it nociplastic only when nociceptive or neuropathic mechanisms cannot fully explain it, recognizing that mixed pain occurs ¹³.

• Pain evoked by light touch, such as clothing, over a sensitized area is allodynia ¹.
• Exaggerated pain from pinprick, a normally painful stimulus, is hyperalgesia ¹.
• Neuropathic pain requires a lesion or disease of the somatosensory system specifically, not of the nervous system in general ¹.
• Nociplastic pain was proposed as a third mechanistic descriptor alongside nociceptive and neuropathic pain, shifting treatment toward normalizing central nervous system function ².
• Viscerosomatic convergence explains why bowel pain can be felt in the back or pelvis ⁴.
• Central sensitization can amplify neuropathic as well as nociplastic pain ².

• Calling diabetic neuropathic pain nociceptive because tissue is "damaged by glucose" ¹.
• Confusing allodynia (non-painful stimulus) with hyperalgesia (painful stimulus) ¹.
• Assuming visceral pain localizes precisely to the organ involved, rather than being referred to somatic areas sharing its spinal segments ⁴.
• Labeling pain psychogenic because no tissue damage or nerve lesion is found, when nociplastic pain is the mechanistic category ².