Horner's syndrome in dogs and cats: 49 cases (1980-1986).

Medical records of 49 dogs and cats with Horner's syndrome were reviewed. Causes included head, neck, and chest trauma, chronic otitis, cranial thoracic mass, and injury attributable to cleaning of the external ear canal. Cause could not be delineated in 54.5% of the dogs. Numerous diagnostic tests and pharmacologic challenge exposure with epinephrine were used to localize the site of injury. Resolution of all clinical signs was observed in 36 animals and required a mean of 7.7 weeks.