Two patients with congenital Horner's syndrome had unilateral facial flushing. Both showed pupillary supersensitivity to epinephrine as well as anhidrosis on the affected side of the face and neck. Facial skin temperature after exercise increased on the intact side, but decreased on the affected side. Thermal vasodilation in the major portions of the face is regulated by sympathetic vasodilator fibres, and less predominantly by adrenergic vasoconstrictor fibres. The asymmetry of facial flushing may have been caused by impaired sympathetic vasodilation and further intensified by active vasoconstriction due to supersensitivity to circulating catecholamine on the affected side.
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