Elsevier

The Lancet

Volume 353, Issue 9170, 19 June 1999, Pages 2145-2148
The Lancet

Series
Visceral pain

https://doi.org/10.1016/S0140-6736(99)01306-9Get rights and content

Summary

Visceral pain is the most common form of pain produced by disease and one of the most frequent reasons why patients seek medical attention. Yet much of what we know about the mechanisms of pain derives from experimental studies of somatic not visceral nociception. The conventional view is that visceral pain is simply a variant of somatic pain, a view based on the belief that a single neurological mechanism is responsible for all pain. However, the more we learn about the mechanisms of somatic and visceral pain, the more we realise that although these two processes have much in common, they also have important differences. Although visceral pain is an important part of the normal sensory repertoire of all human beings and a prominent symptom of many clinical conditions, not much clinical research has been done in this field and there are few clinical scientists with expertise in the management of visceral pain. Instead, visceral pain is usually treated by a range of specialists who take quite different approaches to the management of this type of pain. Thus, the management of visceral pain is frequently unsatisfactory. In this review, we consider visceral pain as a separate form of pain and examine its distinct sensory properties from a clinical perspective. We describe recent research findings that may change the way we think about visceral pain and, more importantly, may help develop new procedures for its management.

Section snippets

Transmission of visceral pain

In the past few years there have been new insights into the neural mechanisms of the clinical features of visceral pain that have challenged the established paradigm. Traditionally, the two schools of thought among pain researchers were: that the viscera are innervated by separate classes of sensory receptors, some concerned with autonomic regulation and some concerned with sensation, including pain; or that internal organs are innervated by a single and homogeneous class of sensory receptors

Biochemistry of visceral pain

There are two distinct biochemical classes of fine calibre unmyelinated primary afferents that innervate somatic and visceral tissues: the first class contain neurones that express peptide neurotransmitters, such as substance P and calcitonin-gene-related peptide (CGRP); and the other class does not express these substances.11 These two classes can also be distinguished by various enzymes, such as fluoride-resistant acid phosphatase found in the nonpeptide group, and receptors, such as the

Wind up: central-nervous-system changes due to visceral afferent signals

Nociceptive afferent discharges in visceral afferents can evoke profound changes in the central nervous system; for example, repetitive noxious stimulation of the viscera evokes increases in the excitability of viscerosomatic neurons in the spinal cord.14 Such changes are highly selective and organised such that they occur on only those viscerosomatic cells that are driven by the conditioning visceral stimulus. In somatic nociceptive systems, a common correlate of the increased excitability is

Central pathways that transmit visceral pain

The traditional view of the transmission of visceral and other types of pain is that signals are carried by crossed anterolateral pathways, mainly the spinothalamic and spinoreticular tracts. This theory, however, has been challenged by the discovery of three previously undescribed pathways that carry visceral nociceptive information: the dorsal column pathway, the spino(trigemino)-parabrachioamygdaloid pathway, and the spinohypothalamic pathway.

The experimental evidence for the importance of

New techniques for study of visceral pain

New electrophysiological and imaging techniques have advanced our understanding of visceral pain perception. Microstimulation of the thalamus, for example, can evoke visceral pain experiences, such as angina or labour pain, sometimes years after the original episode.25, 26 These observations highlight the integrative role of the thalamus in processing memories of pain and the existence of longlived neural mechanisms that are capable of storing the results of a previous painful experience for

Putting research into clinical practice

Most clinical specialists continue to treat visceral pain as just a symptom and not as a distinct neurological entity. Whether or not their patients will obtain effective pain relief will depend on the views of each specialist towards the management of pain. However, it is likely that the findings of basic research into visceral pain will soon start to have an effect on clinical thought and practice. This process is already happening in the management of socalled functional abdominal pain

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