The friction sweat test as a new method for detecting facial anhidrosis in patients with Horner's syndrome.

Forty-eight patients with Horner's syndrome documented by cocaine test were examined with the friction sweat test, a method of detecting a mild sweating asymmetry using alcohol and a standard office prism bar. In all but one patient, the results of the friction test corresponded with the results predicted by the history, physical examination, and Paredrine testing, or with the results of a starch-iodine sweat test. The test is a quick, simple, and reproducible procedure that allows a more accurate determination of the location of the Horner's syndrome at the initial office visit, and therefore assists in determining what tests need to be performed in the further examination of the patient.