Basic and clinical aspects of visceral hyperalgesia.

Although physiological stimuli in the healthy gastrointestinal tract are generally not associated with conscious perception, chronic abdominal discomfort and pain are the most common symptoms resulting in patient visits with gastroenterologists. Symptoms may be associated with inflammatory conditions of the gut or occur in the form of so-called functional disorders. The majority of patients with functional disorders appear to primarily have inappropriate perception of physiological events and altered reflex responses in different gut regions. Recent breakthroughs in the neurophysiology of somatic and visceral sensation are providing a series of plausible mechanisms to explain the development of chronic hyperalgesia within the human gastrointestinal tract. A central concept to all these mechanisms is the development of hyperexcitability of neurons in the dorsal horn, which can develop either in response to peripheral tissue irritation or in response to descending influences originating in the brainstem. Taking clinical characteristics and the concept of central hyperexcitability into account, a model is proposed by which abdominal pain from chronic inflammatory conditions of the gut and functional bowel disorders such as noncardiac chest pain, nonulcer dyspepsia, and irritable bowel syndrome could develop by multiple mechanisms either alone or in combination.