There is no one simple test that can be performed to rule out or confirm a diagnosis of narcolepsy in companion dogs. The veterinarian must rule out a number of other disorders, including primary organic brain disease and other conditions that can cause sleepiness, spasms or seizures such as epilepsy, myasthenia gravis, diabetes and assorted metabolic abnormalities. An initial general database is almost always obtained when a dog comes to the veterinary clinic with a history of unexplained episodes of “falling down” or “passing out.” This includes a thorough history and physical examination, a neurological examination, a urinalysis and routine blood work (a complete blood count and serum biochemistry panel). The results of these tests are typically normal in dogs with narcolepsy, but may be abnormal to various degrees in dogs with underlying primary conditions causing their symptoms.
Several tests can be performed to help diagnose narcolepsy. One is a food-elicited cataplexy test (FECT), the purpose of which is to try to create an exciting, stimulating situation so as to elicit a narcoleptic attack for the veterinarian to observe. This test involves lining up 10 or so bite-sized pieces of tasty food on the ground or floor, spaced about 1 foot apart. The veterinarian will let the dog go and record the time it takes for it to eat all of the treats, together with the number and length of any narcoleptic or cataplectic episodes. Normal dogs usually eat all the food in less than one minute and have no sleep-related, falling or paralytic episodes. Narcoleptic dogs take longer to eat the food and have two or more attacks of varying types.
Certain pharmacologic tests are available as well. These involve administering different drugs that work directly on the dog’s central nervous system and observing for either induction or reduction of narcoleptic episodes. Sometimes, drug-induced tests are used in combination with food-elicited tests. Electrophysiologic tests are available to assess muscle activity during an attack of narcolepsy and assess brain activity for consistency or inconsistency with epilepsy.
Fortunately, narcolepsy is not common and when it does occur in dogs, it usually lasts only a short time and resolves on its own.