Effects of body heating and mental arithmetic on facial sweating and blood flow in unilateral migraine headache.

Facial sweating and pulse amplitude during body heating were investigated during the headache-free period in 38 subjects who suffered from unilateral migraine headache that usually recurred on the same side. In 22 of these subjects, pulse amplitude recorded from the forehead circulation was examined during a computerized mental arithmetic test. Thermally-induced increases in forehead pulse amplitude were smaller on the side habitually affected by headache than on the other side of the forehead. Although sweating from the upper part of the forehead did not differ consistently between the two sides, asymmetry of sweating correlated significantly with asymmetry of the vascular response. Sweating and vascular responses were symmetrical in the cheeks. During mental arithmetic, mean increases in forehead pulse amplitude did not differ consistently between the two sides, but the maximum increase was greater on the nonsymptomatic side. These findings suggest that vascular sympathetic outflow was reduced on the symptomatic side of the forehead, possibly because of damage to the sympathetic plexus surrounding the internal carotid artery in the carotid canal during repeated episodes of migraine. Sympathetic fibers to the upper part of the forehead and cheeks bypass the carotid canal, which may account for symmetrical responses during body heating. A reduction in sympathetic outflow could influence vasodilation at the site of migraine headache.