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Chapter 012. Pain: Pathophysiology and Management (Part 5)

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Sympathetically Maintained Pain Patients with peripheral nerve injury can develop a severe burning pain (causalgia) in the region innervated by the nerve. The pain typically begins after a delay of hours to days or even weeks. The pain is accompanied by swelling of the extremity, periarticular osteoporosis, and arthritic changes in the distal joints. The pain is dramatically and immediately relieved by blocking the sympathetic innervation of the affected extremity. Damaged primary afferent nociceptors acquire adrenergic sensitivity and can be activated by stimulation of the sympathetic outflow. A similar syndrome called reflex sympathetic dystrophy can be produced without obvious. | Chapter 012. Pain Pathophysiology and Management Part 5 Sympathetically Maintained Pain Patients with peripheral nerve injury can develop a severe burning pain causalgia in the region innervated by the nerve. The pain typically begins after a delay of hours to days or even weeks. The pain is accompanied by swelling of the extremity periarticular osteoporosis and arthritic changes in the distal joints. The pain is dramatically and immediately relieved by blocking the sympathetic innervation of the affected extremity. Damaged primary afferent nociceptors acquire adrenergic sensitivity and can be activated by stimulation of the sympathetic outflow. A similar syndrome called reflex sympathetic dystrophy can be produced without obvious nerve damage by a variety of injuries including fractures of bone soft tissue trauma myocardial infarction and stroke Chap. 370 . Although the pathophysiology of this condition is poorly understood the pain and the signs of inflammation are rapidly relieved by blocking the sympathetic nervous system. This implies that sympathetic activity can activate undamaged nociceptors when inflammation is present. Signs of sympathetic hyperactivity should be sought in patients with posttraumatic pain and inflammation and no other obvious explanation. Acute Pain Treatment The ideal treatment for any pain is to remove the cause thus diagnosis should always precede treatment planning. Sometimes treating the underlying condition does not immediately relieve pain. Furthermore some conditions are so painful that rapid and effective analgesia is essential e.g. the postoperative state burns trauma cancer sickle cell crisis . Analgesic medications are a first line of treatment in these cases and all practitioners should be familiar with their use. Aspirin Acetaminophen and Nonsteroidal Anti-Inflammatory Agents NSAIDs These drugs are considered together because they are used for similar problems and may have a similar mechanism of action Table 12-1 . All these