Norepinephrine and epinephrine levels in affected versus unaffected limbs in sympathetically maintained pain.

OBJECTIVE: To test the hypothesis that there is relative sympathetic hyperactivity in the affected limb in patients with sympathetically maintained pain syndromes by measuring serum norepinephrine and epinephrine in the affected versus the unaffected sides.

DESIGN: Venous pool samples were drawn just proximal to the affected area and from an identical site on the unaffected side. Serum norepinephrine and epinephrine were measured by high-pressure liquid chromatography with electrochemical detection.

SUBJECTS: Sixteen women and seven men with a mean age of 44.4 years diagnosed as having sympathetically maintained pain on the basis of a positive response to paravertebral block and a criteria-based diagnostic scheme.

RESULTS: The serum norepinephrine level was significantly lower in the affected limbs than the unaffected limbs (p = 0.024). The serum epinephrine level was not significantly different.

CONCLUSIONS: These results are not consistent with the hypothesis of segmental sympathetic hyperactivity in the affected limb in sympathetically maintained pain and support a hypothesis of peripheral receptor upregulation with pathologic response to circulating catecholamines. Other possible explanations are discussed.