Definition: Pain caused by activation of primary nociceptors (e.g., skin, soft tissues, viscera).
Characteristics:
Easy to localize
Has certain intensity
Time-limited
Typically responds well to short-term use of analgesics like acetaminophen, NSAIDs, COX 2 inhibitors, opioids.
Typical Occurrence: After acute injuries.
2. Visceral Pain
Definition: Due to activation of nociceptors in thoracic, abdominal, or pelvic viscera.
Characteristics:
Diffuse and wide receptive fields
Hard to pinpoint exact location (e.g., stomach ache)
Does not respond to typical nociceptive stimuli
Unique Features:
Viscerosomatic Convergence: Afferent signals from the gut converge with those from other body parts, causing referred pain (e.g., shoulder pain due to diaphragm irritation).
Treatment:
Typical analgesics can help, but identifying specific treatments is ongoing research.
3. Neuropathic Pain
Definition: Injury or dysfunction in the peripheral or central nervous system.
Characteristics:
Described as burning, sharp, lancinating, stabbing, shock-like.
Can occur after thalamic stroke or ridicular pain (e.g., radiating from lower back to leg).
Treatment:
Challenging with common analgesics
Use of anti-neuropathic pain drugs (borrowed from neurology): anti-convulsants, gabapentinoids, etc.
Example: Gabapentin is effective for nerve pain despite being a poor anti-seizure drug.
New Category of Pain
4. Nociplastic Pain
Definition: Dysfunction in central pain processing without an identifiable peripheral cause.