Neuropathic Pain
49. R.L., a 40-year-old, generally healthy woman, suffered a superficial laceration of her left arm at work from a broken glass window. The initial laceration has since healed without complications, but now she is referred for evaluation of pain management because of persistent intolerable pain in her left arm and hand. Physical examination reveals allodynia (pain resulting from a non-noxious stimulus to normal skin) in her left hand and arm. What caused R.L.'s condition, and how would you manage her pain pharmacologically?
Hyperalgesia after a minor injury is well described, but the pathogenic basis of such pain is not understood. In these afflicted patients, the pain threshold is decreased and stimuli response in the affected region is increased. This persistent pain also can be associated with changes in regional cutaneous blood flow, osteoporosis, swelling, changes in regional temperature, and atrophic musculocutaneous changes in the affected region without demonstrable nerve injury. In the affected areas, pain is elicited by even the slightest mechanical or thermal stimuli. This painful hyperalgesic condition, known as, reflex sympathetic dystrophy, or chronic regional pain syndrome (CRPS) has been attributed to sympathetic excess and has been called sympathetically maintained pain (SMP) by some. It also can be the result of other central or peripheral mechanisms that are independent of the sympathetic nervous system. SMP may partially respond to pharmacologic agents that interfere with the α-adrenergic function; therefore, it would be expected to respond to clonidine, prazosin, phenoxybenzamine, or guanethidine. Some symptoms of these syndromes may respond to other classes of pharmacologic agents, such as steroids and NSAIDs, TCAs, anticonvulsants, antiarrhythmics, or local anesthetics.
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