Visceral Referred Pain

Objectives: The perception of pain in regions other than the affected organ is the rule in visceral nociception. This paper reviews the current knowledge about modalities of clinical presentation and pathophysiological mechanisms of visceral referred pain, based on the results of clinical and experimental studies. Findings: Visceral referred pain occurs in somatic areas neuromerically connected with the affected organs where secondary hyperalgesia takes place mostly in deep body wall tissues, extending to superficial layers in repetead/prolonged visceral processes. When two internal organs sharing part of their central sensory projection are affected, visceral pain and referred hyperalgesia from each organ are significantly enhanced ["viscero-visceral hyperalgesia"]. In this case, treatment of one visceral condition significantly improves symptoms from the other. Referred phenomena are mainly sustained by central sensitization processes, involving viscero-somatic or viscero-visceral-somatic convergent neurons, as shown by electrophysiological studies in animal models. A contribution by viscero-somatic reflexes is also present, which would account for the trophic changes of deep body wall tissues that often accompany the hyperalgesia. The expression of visceral referred pain is reduced with the aging process, which renders diagnosis more difficult in the elderly, increasing the risks in life-threatening conditions. Some of the contributing mechanisms may include age-related impaired A-Delta fiber function and a reduction in the content and turnover of neurotransmitter systems involved in nociception. Conclusions: Visceral referred pain and accompanying phenomena are being increasingly understood as regards their pathophysiology. This opens new avenues for treatment strategies that are more mechanism-based and not purely symptomatic.