[A microneurographic analysis of minor reflex sympathetic dystrophy with increased skin sympathetic activity--report of a case].

A 48-year-old man developed swelling, redness, and allodynia in his left palm. Routine physical and neurological examinations revealed no abnormal findings except for left palmar hyperhidrosis. A clinical diagnosis of minor reflex sympathetic dystrophy with causalgia was made. Skin sympathetic activity (SSA), dominating palm sweating and skin vasoconstriction, and discharges of single afferent fiber from the rapidly adapting-type I (RA-I) unit were recorded microneurography from the median nerve at the cubital fossa. SSA obtained from the affected side was significantly increased compared with that from the normal (right) side. The receptive field of RA-I unit in this case was larger than those of normal controls. Enlargement of the receptive field might suggest presence of collateral sprouting in the injured nerve fibers. Allodynia in the left palm was suspected to be resulted from misdirect sprouting between A alpha . beta to A delta . C fibers. Excessive sympathetic out flow to the skin is considered to be the cause of palmar hyperhidrosis, swelling with redness, and lowered pain threshold, since pain threshold is under regulation of SSA. It is concluded that these sensory and autonomic symptoms were resulted from increased sympathetic out flow to the skin and collateral sproutings in the peripheral nerve fibers.