Narcolepsy

Introduction | Causes & Prevention | Symptoms & Signs | Diagnosis & Test | Treatment Options

Narcolepsy

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Introduction

Narcolepsy in dogs is a disorder of the neurological mechanisms that control sleep – especially the state of deep sleep, also known as rapid eye movement sleep (REM). Affected dogs have sudden periods of excessive daytime sleepiness that can include temporary unconsciousness. Narcoleptic episodes are often accompanied by cataplexy, which refers to a temporary loss of muscle control causing partial to complete flaccid (limp) muscle paralysis and/or periods of collapse. Narcolepsy and cataplexy begin during full wakefulness and usually resolve spontaneously. For purposes of these articles, the term "narcolepsy" will be used to include both narcoleptic and cataplectic symptoms, unless otherwise indicated.

Causes & Prevention

Causes of Canine Narcolepsy
Narcolepsy in dogs is thought to have a genetic component. The signs noticed by most owners are the sudden loss of muscle tone and control, called cataplexy. Most affected dogs have no medically detectable central nervous system abnormalities, although rarely some sort of underlying brain disease is found. An inherited form of the disease has been identified in a family of Doberman Pinschers. The gene thought to be responsible for their hereditary disorder involves an abnormality in the receptor for a particular chemical neurotransmitter, hypocretin, that is involved in regulating normal sleep cycles. Most narcoleptic dogs produce normal levels of hypocretin in their brains, but they lack the appropriate receptors for hypocretin, which affects their ability to control various aspects of deep sleep. It has been reported that dogs, people and mice with narcolepsy share a defect in the receptors for this chemical neurotransmitter. Further research is underway to determine the precise cause of narcolepsy in the species that it affects.

Prevention of Narcolepsy in Dogs
Narcolepsy cannot realistically be prevented at this time. However, it rarely requires treatment, unless severe episodes interfere with a dog's safety or overall quality of life.

Special Notes
Diagnosis of narcolepsy is best done at a veterinary teaching hospital or other specialized medical facility. One current treatment protocol involves administering antidepressants. Modafinil is a drug being used in dogs to promote wakefulness. Another is Ritalin, also called methylphenidate, and other treatment options are being pursued. Any treatment should be prescribed and closely supervised by the attending veterinarian. The prognosis for dogs with narcolepsy is fairly good, with consistent management of stressful or otherwise stimulating events.

Symptoms & Signs

Introduction
Dogs are infamous for their frequent napping habits. While naps are quite normal for domestic dogs, sometimes excessive daytime sleepiness is caused by a medical condition called narcolepsy. Narcolepsy is a syndrome in which the sleep-wake cycle is disrupted, causing tiredness, lethargy and brief periods of muscle paralysis or unconsciousness.

Symptoms of Narcolepsy in Dogs
Dogs suffering from narcolepsy periodically (and abruptly) fall into a state of deep sleep during normal waking hours. They often become partially or completely immobilized, and then spontaneously recover. Narcolepsy is neither life-threatening nor painful. Affected animals usually develop one or more of the following symptoms:

Excessive daytime drowsiness
Prolonged periods of sleep during the daytime
Rapid onset of periods of deep sleep, lasting seconds to minutes
Collapse into lateral (lying on the side) or sternal (lying on the stomach) recumbency
Difficulty rousing from sleep
Abrupt loss of consciousness
Abrupt return to consciousness or wakefulness (usually spontaneous)
Paralysis (partial to complete; "cataplexy"; often involves the lower legs or the head and neck)
Muscle twitching (especially around the face, eyes and lower limbs)
Rapid eye movements (REM sleep)
Narcolepsy in dogs is characterized by a condition called cataplexy, which involves brief episodes of partial or complete muscle paralysis with loss of reflexes. Cataplectic episodes are almost always completely and spontaneously reversible. The dog may develop weakness and/or twitching in its leg muscles, and its facial and neck muscles may also be affected. Narcoleptic episodes often occur during times of activity, such as eating, playing, running or other periods of excitement. For example, a dog playing fetch with its owner might suddenly fall into an apparent deep sleep, and then rise and recommence playing as if nothing has happened. These "sleep attacks" tend to be short (seconds to minutes), although they can last up to 30 minutes or more. Most affected dogs can be roused by loud noises, petting, calling their name or other forms of external stimuli. The frequency of narcoleptic symptoms depends upon the severity of the condition in a given dog. Some dogs experience only a few narcoleptic bouts each week or month, while others have dozens of episodes daily. Signs of narcolepsy can mimic signs of other, more serious conditions such as heart disease, diabetes and epilepsy.

Dogs at Increased Risk
Narcolepsy has been diagnosed in many breeds and has an established hereditary component. Predisposed breeds include the Labrador Retriever, Poodle, Dachshund and Doberman Pinscher. Symptoms usually appear by 6 months of age. Small-breed dogs seem to be more severely affected.

Diagnosis & Tests

Introduction
Canine narcolepsy is uncommon and is not an easy condition to diagnose, especially if the attacks are short and infrequent. It is of course best to diagnose narcolepsy when the behavior associated with the condition can be seen by the attending veterinarian, which usually is best accomplished by engaging the dog in play or triggering an episode by presenting highly palatable food treats.

How Narcolepsy is Diagnosed
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.

Special Notes
Fortunately, narcolepsy is not common and when it does occur in dogs, it usually lasts only a short time and resolves on its own.

Treatment Options

Introduction
Narcolepsy is a medical condition that involves excessive daytime sleepiness, lethargy and brief periods of collapse, paralysis and/or unconsciousness that usually resolve completely without treatment. Fortunately, narcolepsy can be managed medically, and there are effective measures that an owner can take to keep their narcoleptic friend safe. The primary goal of treating canine narcolepsy is to reduce the frequency and severity of the cataplectic (paralytic) episodes.

Treatment Options
Treatment is generally only considered if a dog has repeated attacks that interfere with its safety or lifestyle. Narcoleptic episodes themselves do not harm a dog's health. However, they can occur at inopportune times. Narcoleptic dogs that cannot be regularly supervised may be placed on management therapies.

The current medical protocol for dogs with narcolepsy is oral administration of tricyclic antidepressants. These drugs block cellular uptake of certain neurotransmitters, including norepinephrine, and are quite effective at managing the periodic paralysis that typically occurs in dogs with narcolepsy. Oral stimulants are available to relieve daytime sleepiness. Of course, new medications are constantly under development.

Prognosis
Narcolepsy and the associated cataplectic attacks normally are not life-threatening. While there is no cure for this condition, its symptoms can be minimized with medical management. In some cases, the symptoms resolve spontaneously and do not recur.

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