Lacrimation induced by thermal stress in patients with a facial nerve lesion.

I measured facial sweating, flushing, and lacrimation during body heating in 10 patients with a facial nerve lesion compromising parasympathetic outflow. During heating, moisture accumulated in the symptomatic eye of patients with facial nerve palsy, particularly in patients with a long-standing lesion. Sweating and flushing in the forehead were symmetrical. These findings suggest that sympathetic neural discharge during heat stress influences lacrimation in the symptomatic eye of patients with a long-standing facial nerve lesion. Cross-innervation of lacrimal neurons by sympathetic fibers passing through the sphenopalatine ganglion or occupation of degenerated parasympathetic pathways by sympathetic fibers in the periphery could mediate this response.