Autonomic pain: features and methods of assessment.

The distribution of pain originating in the sympathetic nervous system does not match the somatic segmental sensory distribution at the postganglionic level. The two types of distribution are separate and different. At the preganglionic level, fibers show typical segmental sensory distribution, which resembles but is not identical to somatic segmental sensory distribution. Instead, sympathetic pain has its own distribution along the vascular supply and some peripheral nerves. It cannot be called atypical in terms of somatic segmental sensory distribution. Several techniques are available to assess autonomic function in cases of chronic pain. Infrared thermography is superior to any other physiologic or pharmacologic method to assess sympathetic function. Overactivity of sympathetic function in the area of pain is the probable cause of temperature reduction in that area. Accordingly it would appear that in cases in which thermography demonstrates decreased temperature, sympathetic block or sympathectomy would provide relief from the pain.