Delayed onset and resolution of pain - Some observations and implications

Occasionally, pain after disease or trauma develops only after a prolonged interval. Examples include late-onset pains which first occur months or yea rs following a stroke, spinal cord lesion or amputation of a limb; a previo usly experienced pain that is recalled years later; and latent pain trigger ed for the first time by a further insult in the same area. Late-onset pain s may develop gradually or suddenly, and may be brief or long standing. Pai ns which develop after an innocuous insult may be associated with slowly ev olving sensory changes, However, even longstanding pains, particularly thos e of nociceptive origin, may resolve sometimes after many years. Resolution , which again can occur gradually or suddenly, may be spontaneous or follow development of another disorder or after therapeutic intervention. The dur ation of this pain relief can range from minutes to an indefinite period. T hese clinical phenomena, and the mechanisms, including genetic factors, sub serving them, have been little studied. It is postulated that mechanisms im plicated in acute pain may not be the same as those that subserve pain that develops after a long interval. Those late-onset pains which develop slowl y after innocuous lesions may be associated with a variety of slow anatomic al, physiological and biochemical changes, In late-onset pains that follow a painful insult, however, memory of the former pain and threshold triggeri ng factors may be particularly important. Further studies of these neglecte d conditions may lead to understanding of as yet unknown processes subservi ng pain and to novel approaches to treatment.