North American Veterinary Licensing Examination (NAVLE) Practice Test

Horner's syndrome in dogs is characterized by a distinct set of clinical signs resulting from disruption of the sympathetic nerve supply to the eye and surrounding structures. The most common cause of this condition is indeed idiopathic, meaning that the underlying cause is often unknown or cannot be determined despite thorough investigation.

In many cases, idiopathic Horner's syndrome occurs without any identifiable reason and has been observed frequently in breeds such as the Golden Retriever and Collie. The idiopathic nature of this condition often leads to a good prognosis, as many cases resolve spontaneously over time, and typical signs include ptosis (drooping of the eyelid), miosis (constricted pupil), and enophthalmos (recession of the eyeball).

While other conditions like brachial plexus avulsion, neck bite wounds, and otitis media can lead to Horner's syndrome, they are less frequent causes compared to idiopathic origins. Brachial plexus avulsion often results in more severe neurological deficits beyond just Horner's syndrome, and neck bite wounds can also cause a variety of other complications. Otitis media can cause nerve damage leading to the syndrome as well, but it is an atypical source compared to idiopathic cases. Hence, idiopathic remains