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Improving Outcomes in Acute Pain Management: Optimizing Patient Selection: Neuropathic and Nociceptive Pain


Neuropathic and Nociceptive Pain

If we start with the concept of pain as a disease, then treatment begins with a pain diagnosis. Pain pathophysiology comprises 2 categories: nociceptive and neuropathic pain. Nociceptive pain is further divided into visceral and somatic pain, and neuropathic pain is divided into peripheral and central neuropathic pain.

Nociceptive, or somatic, pain is the common discomfort we have all experienced as a result of injury -- a paper cut, a broken bone, or appendicitis, among other things. Somatic pain makes sense to us; we can understand the patient's pain.

Neuropathic pain is associated with injury to a nerve or the central nervous system. Such injuries can give rise to paresthesias, such as numbness, tingling, or electrical sensations. Neuropathic pain can also generate unusual symptoms, such as anesthesia dolorosa, in which the area producing the pain is numb to the touch. This symptom is often puzzling to patients, and some have questioned their own sanity because painful numbness makes no sense. They can pinch the area and not feel the pinch, yet the area is excruciatingly painful. In addition, with nerve, spinal cord, or brain injuries, syndromes (such as allodynia) can develop and ordinarily non-noxious stimuli (such as light pressure or stroking) cause pain.

An in-depth discussion of nociceptive and neuropathic pain is beyond the scope of this column, but the key concepts are straightforward: Nociceptive pain is typically responsive to anti-inflammatory agents and opiates, whereas, for unclear reasons, neuropathic pain is often poorly responsive to these agents. Recent studies suggest that in neuropathic pain, anatomic and physiological changes occur within the spinal cord and perhaps the brain. These consequences of central nervous system plasticity mean that some of the processes that generate neuropathic pain may, over a relatively short period of time, become hardwired into the nervous system.[11]

Postoperative and posttraumatic pain are primarily nociceptive and not neuropathic in nature. A simple fracture produces somatic nociceptive pain and should respond to an anti-inflammatory or opiate. A stone in the ureter produces visceral somatic pain and often responds well to an anti-inflammatory or opiate. Despite the fact that most acute pain is nociceptive, there are relatively common acute situations in which nociceptive and neuropathic pain occur together. An example is the patient with an acute herniated disc who experiences somatic nociceptive pain from the disruption of the disc and neuropathic pain from compression and inflammation of the nerve root. Thus, in this case, treatment should be directed at both the somatic and neuropathic pain components.

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