The ABC Syndrome
Recently Ochoa (58) described a newly recognized painful syndrome in a small group of patients. He believes this syndrome represents a subset of causalgia/RSD, and he calls it the ABC (Angry Backfiring C nociceptor) syndrome. This syndrome has been found in patients with major sciatic nerve injury, diabetic neuropathy, and other neuropathic disorders. The following are the characteristics of the syndrome: (a) stimulus-induced pain in response to low-intensity skin stimulation (hyperalgesia, allodynia) and often spontaneous burning pain; (b) induced pain is characteristically elicited by both mechanical and thermal stimuli—he named this polymodal hyperalgesia (PH); © in most patients decreasing the skin temperature abolishes both spontaneous and mechanically induced pain, whereas increasing the temperature aggravates both symptoms. Less often this thermal dependence is reversed (i.e., cold aggravates and heat relieves the pain), and in still other more unfortunate patients, the thermal dependence is bipolar, expressing aggravation by either increasing or decreasing the temperature. He termed such influence of one stimulus energy on the perception threshold of another cross-modality threshold modulation (XTM); (d) vasodilation with warming of symptomatic skin as best revealed by thermography is a key sign of the syndrome; and (e) symptoms that are up-modulated by increased temperature may worsen during sympathetic blocks. As discussed in some detail in the section C, Ochoa believes this syndrome is due to sensitization of polymodal nociceptors (CPNs) and that the most rational therapeutic strategy is drug- induced desensitization of CPNs.


http://neuro.vetmed.ufl.edu/neuro/Jo...es/CPS_Art.htm