Sensory testing of pathophysiological mechanisms of pain in patients with reflex sympathetic dystrophy.

The incidence of 3 sensory abnormalities was studied among 17 patients with a diagnosis of reflex sympathetic dystrophy (RSD) and 14 patients with persistent limb pain following trauma; the extent to which the 3 abnormalities were associated with each other and with the intensity of spontaneous clinical pain were also studied. These abnormalities included (1) heat-induced hyperalgesia (54.8% of 31 patients tested); (2) low-threshold A beta-mediated (45.2%) or high-threshold (54.8%) mechanical allodynia; and (3) slow temporal summation of mechanical allodynia (10 of 29 patients tested). These 3 sensory abnormalities occurred to widely varying extents and were not reliably associated with each other. As hypothesized, patients with temporal summation had significantly more intense spontaneous pain than those who did not demonstrate this sensory characteristic. In contrast, the presence or absence of thermal hyperalgesia and type of allodynia did not appear to influence the intensity of spontaneous pain. These results indicate that variable types of primary afferents (i.e., A beta versus A delta, C) and/or varying extents of abnormal spatial summation mechanisms trigger pain responses among RSD patients and that at least one of these, slow temporal summation, is likely to contribute to the intensity of a patient's ongoing pain.