lack of uniform definitions and a comprehensive classification system (Burchiel and Hsu, 2001). The lack of definitions was addressed in 2000 with the release of a proposed scheme by the International Association for the Study of Pain for characterization of the pain associated with spinal cord injuries. By using those new definitions, a prospective study of 100 people found that 5 years after injury, 81 percent reported pain (of all types), and 58 percent reported that their pain was “severe or excruciating” (Siddall et al., 2003). The impact of chronic pain may be so great—deterioration of quality of life, ability to function, self-image, and care delivery—that depression and thoughts of suicide are common (Cairns et al., 1996).
The new classification system organizes spinal cord injury pain under two broad categories—nociceptive and neuropathic—along with five subclassifications (each of which has further clinical subtypes and possible pathologies; see Table 2-8). Nociceptive pain arises from an external source (e.g., a noxious stimulus and consequent tissue damage), whereas neuropathic pain arises from the pathological changes occurring within sensory neurons or pathways. The two types of nociceptive pain—musculoskeletal and visceral—were reported by 59 and 5 percent of patients, respectively, in the prospective trial cited above (Siddall et al., 2003). Of the three types of neuropathic pain, 41 percent of patients reported at-level neuropathic pain, whereas 34 percent reported below-level neuropathic pain (Siddall et al., 2003).
Nociceptive pain is the dull and aching pains that one encounters when a limb is broken or when one has lower back pain. Painful stimuli are registered by specialized sensory cells known as nociceptors. Nociceptors, which are intact with this type of pain, respond to local damage to nonneural tissues (e.g., bone, muscles, and ligaments).
Neuropathic pain, on the other hand, is produced by direct damage to neural tissue. It is described as a sharp, shooting, burning, or electrical type of pain. Sensory neurons and pathways undergo physiological alterations; they may become exquisitely sensitive, firing off impulses out of proportion to the stimulus (hyperesthesia) or even without an external trigger whatsoever. They may register the light touch of a feather as an unpleasant burning sensation (dysesthesia) instead of a pleasant one.
Nociceptive pain and neuropathic pain have distinct causes and, as a result, distinct treatments. Because nociceptive pain arises from tissue damage and not from nerve pathology, it is often treated with standard therapies, most commonly physical therapy, various pain medications, and surgical therapy. Neuropathic pain is more difficult to treat, partly because its mechanisms are still being uncovered. The distinction between the two types of pain, however, is not always clear-cut (Bryce and Ragnarsson, 2002). Over time, nociceptive pain can lead to the sensitization of spinal