Horner syndrome is a condition characterized by a drooping upper lip, narrow pupils, and recessed eyeballs caused by nerve damage in dogs. While Horner syndrome may be the result of a number of diseases and illnesses, damage to the nerves in the face is the central cause of the condition. Muscles in the face are no longer stimulated by the sympathetic nerves because of some injury. In fact, the most common causes of Horner syndrome in dogs include car accidents, bite wounds, IV disc disease, middle ear infections, brain or chest cancer, and even some medications while as many as half of Horner syndrome cases have no known cause. Moreover, Horner syndrome is particularly common in Golden Retrievers.
Your veterinarian will diagnose Horner syndrome first by looking for the tell-tale signs of the disease (drooping lip, narrow pupils, etc) and then through a complete physical and neurological exam. Generally, your vet will order x-rays, blood tests, and maybe even a CAT scan or MRI to identify the cause of the syndrome. After correctly diagnosing the disease, most treatments focus on ameliorating the underlying cause but the location of injury is also very important.
First of all, phenylephrine drops are prescribed as they can treat the visible signs of the disease. Other than that, your vet will want to treat the main cause. A bite wound or middle ear infection would be treated according to your vet’s advice. In cases where the cause of Horner syndrome in dogs is unknown, clinical signs are treated and normally the syndrome clears up on its own in 6 to 8 weeks. When the syndrome is caused by injury outside the brain and spinal chord, prognosis is usually better than when damage occurs to the nerves inside the brain and spinal chord.