Porth's Essentials of Pathophysiology, 4e

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Somatosensory Function, Pain, and Headache

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result from partial or complete loss of descending inhib- itory pathways or spontaneous firing of regenerated nerve fibers. They include conditions such as causalgia, phantom limb pain, and postherpetic neuralgia. Central pain, which is associated with disease or injury of the CNS, is characterized by burning, aching, hyperalgesia, dysesthesia, and other abnormal sensations, and is expe- rienced as superficial (skin) or deep (bone or muscle) pain. It is associated with conditions such as thalamic lesions, spinal cord injury, surgical interruption of pain pathways, and multiple sclerosis. Unlike acute pain, chronic pain serves no useful pur- pose. It imposes physiologic, psychological, interper- sonal, and economic stresses and may exhaust a person’s resources. It is often associated with loss of appetite, sleep disturbances, and depression, which commonly is relieved once the pain is removed. Chronic pain management is complex and treatment depends on the cause of the pain, the natural history of the underlying health problem, and the life expec- tancy of the individual. 20,21 If the organic illness causing the pain cannot be cured, then noncurative methods of pain control become the cornerstone of treatment. Chronic pain is best handled by a multidisciplinary team that includes specialists in areas such as anesthe- siology, nursing, physical therapy, social services, and surgery. Cancer is a common cause of chronic pain. 23–25 The goal of chronic cancer pain management should be pain alleviation and prevention. Preemptive therapy tends to reduce sensitization of pain pathways and provides for more effective pain control. Pharmacologic and non- pharmacologic interventions are the same as those used for other types of chronic pain. Depending on the form and stage of the cancer, other treatments such as pal- liative radiation, antineoplastic therapies, and palliative surgery may help to control the pain. In 1986, the World Health Organization (WHO) developed a three-step ladder that assists clinicians in choosing the appropri- ate analgesic medications. 26 Step 1 involves the use of nonopioid analgesics, and steps 2 and 3 involve the use of opioid analgesics. Pain Management Careful assessment of pain assists clinicians in diagnos- ing, managing, and relieving the patient’s pain. As with other disease states, eliminating the cause of the pain is preferable to simply treating the symptom. Assessment Assessment includes such things as the nature, sever- ity, location, and radiation of the pain. Reports of pain are almost entirely subjective. A careful history often provides information about the triggering factors (i.e., injury, infection, or disease) and the site of nociceptive stimuli (i.e., peripheral receptor or visceral organ). 21 A comprehensive pain history should include pain onset; description, localization, radiation, intensity, quality, and pattern of the pain; anything that relieves or exacerbates it; and the individual’s personal reaction to the pain.

The single most reliable indicator of the existence and intensity of acute pain is probably the person’s self-report. Unlike many other bodily responses, such as tem- perature and blood pressure, the nature, severity, and distress of pain cannot be measured objectively. To over- come this problem, various methods have been devel- oped for quantifying pain based on the person’s report. They include numeric pain intensity, visual analog, and verbal descriptor scales. Most pain questionnaires assess a single aspect of pain such as pain intensity. For exam- ple, a numeric pain intensity scale would have patients select which number best represents the intensity of their pain, where 0 represents no pain and 10 represents the most intense pain imaginable. A visual analog scale also can be used; it is a straight line, often 10 cm in length, with a word description (e.g., “no pain” and “the most intense pain imaginable”) at each of the ends of the line representing the continuum of pain intensity. Nonpharmacologic Interventions A number of nonpharmacologic methods of pain control are used in pain management. These include cognitive- behavioral interventions (e.g., relaxation, distraction, imagery, and biofeedback), physical agents (e.g., heat and cold), electroanalgesia (transcutaneous electrical nerve stimulation [TENS]), and acupuncture. Often these meth- ods are used in addition to analgesics rather than as the sole form of pain management. PharmacologicTreatment Pharmacologic treatment involves the use of drugs in the management of pain. It includes the use of nonnarcotic and narcotic analgesics, as well as adjuvant medications, such as antidepressants, anticonvulsants, and muscle relaxants. Topical medications (e.g., fentanyl patch) are a new aspect of pain management, whose full potential has yet to be determined. An analgesic drug is a medication that acts on the nervous system to decrease or eliminate pain without inducing unconsciousness. Analgesic drugs do not cure the underlying cause of the pain, but their appropriate use makes the pain more tolerable and, in the case of acute pain, may prevent it from progressing to chronic pain. The ideal analgesic would be effective and nonad- dictive and produce minimal adverse effects. Although long-term treatment with opioids can result in opioid tolerance (i.e., increasingly greater drug dosages being needed to achieve the same effect) and physical depen- dence, this should not be confused with addiction. Long-term drug-seeking behavior is rare in persons who are treated with opioids only during the time that they require pain relief. The unique needs and circumstances presented by each person in pain must be addressed to achieve satisfactory pain management. Nonnarcotic Analgesics. Nonnarcotic oral analgesic medications include aspirin, other NSAIDs, and acet- aminophen. Aspirin (acetylsalicylic acid) acts periph- erally and centrally to block the transmission of pain impulses. It also has antipyretic and anti-inflammatory properties. The action of aspirin and other NSAIDs is