Innervation of sweat glands in the forehead. A study in patients with Horner's syndrome.

The amount of sweating in lateral and medial sites in the forehead was investigated with quantitative evaporimetry in 18 patients with Horner's syndrome: eight cases with a central (1st), five with a preganglionic (2nd), and five with a postganglionic (3rd) neurone lesion. The amount of sweating was measured after body heating, and, at another occasion, after intracutaneous injection of the cholinergic drug pilocarpine. The two sites were at the root of the nose (medial position) and at the lateral angle of the eye (lateral position). Generally, there was a reduced level of sweating on the symptomatic versus the non-symptomatic side in both positions during body heating, except in the lateral part of the forehead in the 3rd neurone lesions, where sweating was greater on the symptomatic than on the non-symptomatic side. There was a nearly symmetrical sweating response after pilocarpine injection at all sites. There was one exception to this rule; the lateral position in the preganglionic neurone lesion group where pilocarpine induced more sweating on the non-symptomatic side. Thus, the results suggest a relative supersensitivity to pilocarpine in the medial position for all patients and in the lateral position for the central neurone lesion group. The findings suggest that the innervation of sweat glands in the medial and lateral parts of the forehead is different, the medial part being supplied by nerve fibres from the sympathetic plexus of the internal carotid artery, while the sweat glands in the lateral part is furnished from the plexus surrounding the external carotid artery.