Phantom-limb pain

Treatment of pain in children after limb-sparing surgery: an institution's 26-year experience

A significant proportion of patients report long-term pain that is ≥5 on a 0-10 intensity scale after limb-sparing surgery for malignancies of the long bones. Patients experience several distinct types of pain after limb-sparing surgery which constitute a complex clinical entity. This retrospective study examined 26 years of experience in a pediatric institution (1981-2007) in pain management as long as 6 months after limb-sparing surgery and reviewed the historical evolution of pain interventions. One hundred fifty patients underwent 151 limb-salvage surgeries for bone cancer of the extremities in this series. Pain treatment increased progressively in complexity. Therapies included opioids, nonsteroidal antiinflammatory drugs, acetaminophen-opioid combinations, postoperative continuous epidural infusion, anticonvulsants and tricyclic antidepressants for neuropathic pain, local anesthetic wound catheters, and continuous peripheral nerve block catheters. Management of pain after limb-sparing surgery has evolved over the 26 years of this review. It currently relies on multiple "layers" of pharmacologic and nonpharmacologic strategies to address the complex mixed nociceptive and neuropathic mechanisms of pain in this patient population.

Central neuroplasticity and pathological pain

The traditional specificity theory of pain perception holds that pain involves a direct transmission system from somatic receptors to the brain. The amount of pain perceived, moreover, is assumed to be directly proportional to the extent of injury. Recent research, however, indicates far more complex mechanisms. Clinical and experimental evidence shows that noxious stimuli may sensitize central neural structures involved in pain perception. Salient clinical examples of these effects include amputees with pains in a phantom limb that are similar or identical to those felt in the limb before it was amputated, and patients after surgery who have benefited from preemptive analgesia which blocks the surgery-induced afferent barrage and/or its central consequences. Experimental evidence of these changes is illustrated by the development of sensitization, wind-up, or expansion of receptive fields of CNS neurons, as well as by the enhancement of flexion reflexes and the persistence of pain or hyperalgesia after inputs from injured tissues are blocked. It is clear from the material presented that the perception of pain does not simply involve a moment-to-moment analysis of afferent noxious input, but rather involves a dynamic process that is influenced by the effects of past experiences. Sensory stimuli act on neural systems that have been modified by past inputs, and the behavioral output is significantly influenced by the "memory" of these prior events. An increased understanding of the central changes induced by peripheral injury or noxious stimulation should lead to new and improved clinical treatment for the relief and prevention of pathological pain.

Amputation and the prevention of phantom pain

Although it has been proposed that preoperative analgesia with epidural administration of analgesics may prevent long-term phantom pain, published results to date have been contradictory and controversial. In this case report, we describe a 41-year-old man with local recurrence of squamous cell carcinoma of the anus who underwent a hemipelvectomy. Preoperatively he had a significant neuropathic pain syndrome requiring oxycodone 60 mg every 4 hours. An epidural infusion of morphine and bupivacaine was started 24 hours preoperatively and discontinued on the third postoperative day. Over the next 10 days the oxycodone was gradually decreased and eventually discontinued prior to discharge. A review of the literature reveals conflicting reports on the benefit of preoperative epidural pain management in the prevention of postoperative pain syndromes. Conflicting research and conclusions of commentators leaves unanswered questions for clinicians. Nevertheless, we do know that we need to provide the best pain relief for patients both before and after amputation. This may require a combination of the oral, subcutaneous or intravenous, and epidural routes.