The relationship between thermographic asymmetry in various parts of the face and indices of ocular sympathetic outflow was examined in 80 patients with unilateral migrainous headache. Both during and between episodes of headache, the pupil on the symptomatic side dilated more slowly and less extensively in darkness than the opposite pupil, indicating that ocular sympathetic outflow was compromised in some patients. In such cases the upper forehead and orbital region were warmer on the symptomatic side during migraine. In contrast to these signs of a reduction in cervical sympathetic outflow, eyelid separation was greater on the symptomatic side in patients with headache on the side that was usually affected. During the headache-free interval no consistent thermographic asymmetry was detected and eyelid separation was similar on both sides. These findings suggest that extracranial vascular changes and ocular sympathetic dysfunction during migraine are secondary to activation of trigeminal-vascular reflexes or to antidromic release of vasoactive substances from trigeminal nerve terminals. A secondary deficit in the sympathetic pathway to the symptomatic pupil could also prevent the expression of an increase in sympathetic outflow during headache.
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