Plasma neuropeptide Y in the symptomatic limb of patients with causalgic pain.

The aim of this experiment was to measure the concentration of neuropeptide Y (NPY), a vasoactive transmitter which co-exists with noradrenaline in sympathetic nerve terminals, in venous blood taken from the painful and contralateral limbs of 16 patients with features of reflex sympathetic dystrophy (RSD) or causalgia. In nine patients tapping the skin of the affected limb provoked pain (allodynia). In seven of the nine patients with allodynia the concentration of NPY was lower on the painful side; similar results were obtained in only two of seven patients without widespread allodynia. In addition, the concentration of NPY was generally lower in the painful limb if it was warmer than the contralateral limb. These findings suggest that a reduction in sympathetic activity might accompany allodynia and influence vasomotor disturbances in patients with causalgic pain.