Autonomic asymmetry in migraine: augmented parasympathetic activation in left unilateral migraineurs.

Brain autonomic control is asymmetrical, the left hemisphere affecting predominantly parasympathetic function and the right hemisphere affecting predominantly sympathetic function. It is not known whether the extent of autonomic activation is altered in migraine, although the fact that some migraineurs express parasympathetic features such as facial flushing, lacrimation and rhinorrhoea might suggest increased parasympathetic activation. We instilled diluted soapy eyedrops and measured (i) the trigemino-parasympathetic reflex by the vasodilator response of forehead skin bilaterally using photoplethysmography; (ii) the somato-sympathetic reflex by vasoconstriction in the index finger; and (iii) heart rate response. We studied 14 left-sided and 15 right-sided unilateral migraineurs outside attacks. We found that left-side migraineurs had significantly higher bilateral parasympathetic vasodilatation, regardless of the stimulation or measurement side (+60.1 +/- 6.4%) compared with right-side migraineurs (+41.9 +/- 6.4%, P < 0.05). Sympathetic vasoconstriction, however, was similar for the two groups (left, -15.9 +/- 4.2%; right, -17.7 +/- 4.1%, NS). Bradycardia was significantly more pronounced for the left-side migraineurs (interbeat, RR interval increase of +6.2 +/- 1.1% versus +3.1 +/- 1.1%, P < 0.04). We conclude that unilateral left-side migraineurs have increased parasympathetic activation in response to pain compared with right-side migraineurs. Sympathetic responses were similar in the two groups and seemed not to be affected by migraine side. Since cranial parasympathetic activity induces cerebral vasodilatation, this augmentation might be an inherent part of the migraine pathophysiology in these patients.

Different patterns of parasympathetic activation in uni- and bilateral migraineurs.

Several lines of evidence support involvement of the parasympathetic system in migraine: (i) migraine-associated symptoms, such as exaggerated facial flushing, lacrimation and rhinorrhea; (ii) increased levels of cranial venous vasoactive intestinal peptide in migraineurs during attacks; and (iii) reports of migraine pain alleviation by intranasal instillation of lidocaine, which can block some of the parasympathetic outflow to the cranium. This study assessed cranial parasympathetic function in migraineurs in between attacks, assuming that abnormal function might imply involvement of the parasympathetics in migraine pathogenesis. We tested 39 female migraineurs outside attacks, of whom 11 had bilateral pain, 20 unilateral at a specific side and eight alternating unilateral head pain, and 16 controls. The trigemino-parasympathetic reflex was studied, using soapy and saline eye drops for stimulation of the afferent limb of the reflex arch, and cutaneous vascular response at the forehead for the efferent limb. The latter was recorded by photoplethysmography on both sides of the forehead. We found no difference in vasodilatation between migraineurs as a group and controls (83.7 +/- 6.5% and 80.8 +/- 7.6%, respectively, not significant). However, when analysing data by the site of pain, we found that those with bilateral pain had the largest vasodilatation response (141.6 +/- 16.2%, P < 0.05 versus controls, analysis of varance, post hoc Tukey-Kramer HSD), while those with unilateral pain had the least vasodilatation (45.5 +/- 3.3%, P < 0.05). The response of patients with alternating pain (97.2 +/- 12.6%) did not differ from controls. It is concluded that cranial parasympathetic function does differ among patients with various migraine types at rest. Based on the understanding of dysfunctional brainstem pain modulation in migraine, we suggest a model of within-brainstem interaction between the two locus coeruleus nuclei, which are involved in control of pain and cranial parasympathetic outflow. The model assumes various levels of inhibitory inter-relationships between these two nuclei; diminution or absence of the normal reciprocal inhibitory relationships between them may underlie the augmented cranial parasympathetic response in bilateral migraineurs, while an excess of reciprocal inhibitory relationship between them may underlie the diminished cranial parasympathetic response in unilateral migraineurs. These findings might help in clarifying inter-relationships between brainstem nuclei in the context of migraine pathogenesis.