Nociceptive (somatic)

Nociceptive (somatic) pain is linked to tissue damage to the skin, musculoskeletal system, or viscera (visceral pain), but the sensory nervous system is intact, as in arthritis or spinal stenosis. It can be acute or chronic. It is mediated by the afferent A-delta and C-fibers of the sensory system. The involved afferent nociceptors can be sensitized by inflammatory mediators and modulated by both psychological processes and neurotransmitters like endorphins, histamines, acetylcholine, serotonin, norepinephrine, and dopamine.

Neuropathic pain 

Neuropathic pain is a direct consequence of a lesion or disease affecting the somatosensory system. Over time, neuropathic pain may become independent of the inciting injury, becoming burning, lancinating, or shock-like in quality, It may persist even after healing from the initial injury has occurred. Mechanisms postulated to evoke neuropathic pain include central nervous system brain or spinal cord injury from stroke or trauma; peripheral nervous system disorders causing entrapment or pressure on spinal nerves, plexuses, or peripheral nerves; and referred pain syndromes with increased or prolonged pain responses to inciting stimuli. These triggers appear to induce changes in pain signal processing through "neuronal plasticity," leading to pain that persists beyond healing from the initial injury.

Central sensitization

In central sensitization pain, there is alteration of central nervous system processing of sensation, leading to amplification of pain signals. There is a lower pain threshold to nonpainful stimuli, and the response to pain may be more severe than expected. Mechanisms are the subject of ongoing research. An example is fibromyalgia, which has a strong overlap with depression, anxiety, and somatization disorders and responds best to medications that modify neurotransmitters like serotonin and dopamine.

Psychogenic pain 

Psychogenic pain involves the many factors that influence the patient's report of pain—psychiatric conditions like anxiety or depression, personality and coping style, cultural norms, and social support systems. 

Idiopathic pain 

Idiopathic pain is pain without an identifiable etiology

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