Vestibular Syndrome

History. A 3-year-old male cocker spaniel is brought to your clinic. The owner states that for the previous 2 days, the dog has held his right ear lower than his left ear. He also tends to walk in circles, clockwise to the right.

Clinical Examination. On physical examination of the dog, you find that the outer ear infection persists. You also confirm that the dog persistently tilts his head with the right ear down and circles to the right; you Iind that he has a spon­taneous horizontal nystagmus. Results of the remaining phy­sical and neurological examination are within normal limits.

Comment. Head tilt, circling, and spontaneous nystagmus constitute a common constellation of clinical signs often called the vestibular syndrome. It results from abnormality in the vestibular system, usually in the membranous labyrinth. It is frequently caused by the extension of an infection from the outer and middle ear to the labyrinth of the inner ear. This results in an abnormal balance of action potential frequencies between the normal and abnormal sides of the vestibular sys­tem, causing asymmetric stimulation of the ocular and pos­tural reflex mechanisms normally controlled by the vestibular nuclei.

Treatment. When such labyrinthitis is caused by bacterial infection, treatment with appropriate antibiotics is often effective in eliminating the clinical signs by returning the peri­pheral receptor to its normal function. In cases of idiopathic vestibular syndrome in older cats and dogs, spontaneous recovery, without treatment, is common.