Idiopathic facial paralysis in the dog.

Facial nerve paralysis of acute onset is reported in seven mature dogs, five of which were cocker spaniels. The clinical signs were characterised by ear drooping, lip commissural paralysis, sialosis, and collection of food on the paralysed side of the mouth. All dogs showed absent menace responses and trigeminofacial/acousticofacial reflexes. Horner's syndrome was not present in any dog. In four dogs, bilateral facial paralysis developed. The facial paralysis was unrelated to otitis media. Electrodiagnostic studies revealed denervation potentials and absent evoked muscle potentials. Facial nerve biopsies from two cases showed nerve fibre degeneration and apparent loss of larger diameter myelinated fibres. The condition has been termed idiopathic facial paralysis since the aetiopathogenesis is presently unknown.