78: Chronic Pain Management

Published on 06/02/2015 by admin

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CHAPTER 78 Chronic Pain Management

Ronald Valdivieso, MD

1 What is the definition of pain?

The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Acute pain is associated with an identifiable cause (e.g., surgery, trauma, acute illness) and usually resolves with healing. Chronic pain is more difficult to define. It is believed that pain becomes chronic if it persists beyond 1 month of the usual course of an acute problem. However, other authors do not believe that duration should be identified as one of the distinguishing features of chronic pain and point to cognitive-behavioral aspects as essential criteria in any chronic pain syndrome.

2 How does normal pain perception occur?

Nociceptors are structures located at the end of axons that are depolarized by noxious thermal, mechanical, or chemical stimuli. The distal ends of most A-δ and C fibers are nociceptors. These axons are the ones that carry nociceptive information to the dorsal root and trigeminal ganglion and enter the spinal cord via the posterior root. Once in the spinal cord these afferent fibers synapse with cells in Rexed’s laminae I and V preferentially but also in laminae II and X. Axons from the previously mentioned neurons that travel to the contralateral side of the spinal cord will eventually form the spinothalamic tract, spinoreticular tract, and spinomesencephalic tract. Axons that enter the dorsal column will form the postsynaptic dorsal column tract. These ascending nociceptive tracts will eventually synapse with superior structures such as the periaqueductal gray, hypothalamus, and thalamus. The ventroposterolateral, ventroposteromedial, and ventroposteroinferior nuclei of the thalamus then send projections to the somatosensory cortex and cingulated cortices.

3 What is the classification of pain based on neurophysiologic mechanisms?

Pain can be classified according to its neurophysiologic mechanism:

image Nociceptive pain: Occurs when nociceptors are stimulated by noxious stimuli. This category is divided into somatic and visceral pain. Somatic pain sensation originates from trauma, burns, and ischemia, to name the most common ones. It is transmitted via somatic nerves. Visceral pain, as its name implies, originates from visceral structures. It is transmitted preferentially via the sympathetic fibers and is usually produced by distention, ischemia, or spasm of hollow viscera.
image Neuropathic pain: Is pain produced by an alteration in structure or function of the nervous system. Neuropathic pain can be divided into peripheral and central. Examples of peripheral neuropathic pain include CRPS II (causalgia), postherpetic neuralgia, diabetic neuropathy, and radicular pain from mechanical compression. Central neuropathic pain syndromes include poststroke pain, postparaplegic pain, and pain syndromes from multiple sclerosis.
image Psychogenic pain: Is quite controversial in the sense that it is very difficult to define. One popular definition is that this pain is better described and understood in psychologic rather than physical language and is pain for which an adequate physical explanation cannot be found.

4 Name the most commonly used groups of medications for the treatment of chronic pain

See Table 78-1.

TABLE 78-1 Commonly used Groups of Medications for Treatment of Chronic Pain

image

5 How are nerve blocks helpful in the treatment of chronic pain?

image Diagnosis: Nerve blocks can help identify the nerve site responsible for the symptoms.
image Therapy: Nerve blocks temporarily reduce pain and therefore facilitate physical therapy. Based on the response to a diagnostic block, it might be possible to determine if a neuroablation procedure is appropriate to treat a given condition.

6 Are psychosocial factors important in the diagnosis and treatment of pain?

Painful disorders can present with associated psychologic or psychiatric symptoms. These can vary from mild depression to obvious substance abuse problems to suicidal thoughts. It is necessary to address such issues to improve the patient’s chance for recovery.

7 How is pain of malignant origin treated?

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