Cutaneous pain threshold changes after sympathetic block in reflex dystrophies

Abstract

In a group of 30 human subjects suffering from sympathetic reflex dystrophies of the limbs, the sympathetic ganglia of the affected side were blocked with a local anesthetic. Using an original method, the cutaneous pain threshold was measured before the block and at prefixed intervals after the block during a period of 2 days. In all subjects the cutaneous pain threshold showed damped oscillations both in the limb ipsilateral to the block and in the contralateral one. The analysis of these oscillations showed that the sympathetic control of the cutaneous pain threshold may be exerted through a negative feedback loop (skin-afferent input-CNS-sympathetic output-skin); and that the afferent discharge of a limb controls the contralateral sympathetic output through central mechanisms.