Inherited respiratory disorders

Laryngeal paralysis

roblib — Fri, 30 Apr 2010 16:55:43 +0000

What is ... ?:

In this disorder, there is some loss of function in the laryngeal muscles that normally open the larynx when an animal breathes in. This is caused by degeneration of certain nerves involved in normal breathing. The result is airway obstruction, to varying degrees, causing loud and labored respiration.

In the Dalmatian, this condition is part of a more widespread condition of the nervous system called laryngeal paralysis-polyneuropathy complex.
In the inherited form, signs are usually seen before 6 months of age. Laryngeal paralysis due to other causes is also seen in older dogs of other breeds.

How is ... inherited?:

In the Bouvier and the Siberian husky, inheritance is autosomal dominant. In the Dalmatian it is autosomal recessive.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Signs of this disorder are usually seen by 2 to 6 months of age and are often first noticed, or become worse, in hot weather. Affected dogs have difficulty breathing, and may collapse, especially with exercise. Your dog's breathing will be noisy, with coughing or gagging when eating, and you may notice that the gums are greyish rather than pink.

As part of the laryngeal paralysis-polyneuropathy complex, affected Dalmatians commonly have megaesophagus, which is a chronic dilation (expansion) of the esophagus that occurs due to loss of normal muscle tone and function, so that swallowing can not occur normally. Affected dogs regurgitate undigested food after meals, and may develop aspiration pneumonia due to inhalation of food particles or other foreign matter.

How is ... diagnosed?:

Your veterinarian will suspect a problem of airway obstruction based on what you describe and on your dog's breathing pattern. Laryngoscopy (looking down your dog's throat with a light) will confirm laryngeal paralysis as the cause.

How is ... treated?:

Initial treatment is aimed at calming your dog and lessoning repiratory distress. Depending on the severity of the obstruction, this may require mild sedation, administration of oxygen, and low doses of corticosteroids to reduce swelling. Rarely, with very severe breathing problems, a veterinarian may need to put a tube into a dog's trachea (an emergency tracheostomy).

Once your veterinarian has assessed your dog, s/he will discuss with you management of this condition. In mild cases, all that may be required is avoidance of stress, especially associated with exercise and heat, and occasional medical treatment as above for episodes of respiratory distress. Where the condition is more severe, your veterinarian may suggest surgery to tie back the muscles and enlarge the opening of the larnyx.
Unfortunately the outlook is guarded to poor for Dalmatians with laryngeal paralysis-polyneuropathy complex. Most die or are euthanized within a few months of diagnosis, due to aspiration pneumonia.

For the veterinarian:

Laryngeal function can best be assessed when the dog is very lightly anesthetized. On inspiration one or both vocal folds will not abduct normally, and the glottis will collapse. Electromyography can be used to test the function of the laryngeal muscles.

Other neurologic signs in Dalmatians with laryngeal paralysis-polyneuropathy complex may appear before, at the same time as, or after the development of signs relating to respiratory distress. Signs of neurologic dysfunction may include hyporeflexia, proprioceptive deficits, hypermetria, and paresis. Megaesophagus is common in these dogs.

Breeding advice:

Affected dogs should not be bred. In the Bouvier and husky, where inheritance is autosomal dominant, close relatives should be carefully evaluated for signs of this problem before being used for breeding.

Due to the autosomal recessive mode of inheritance in the Dalmatian and possibly the bull terrier, breeding of the parents (carriers of the disorder) and siblings (suspect carriers) should be avoided.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Braund KG. 1995. Peripheral nerve disorders. In EJ Ettinger and EC Feldman(eds.) Textbook of Veterinary Internal Medicine, p. 701-726. WB Saunders Co., Toronto.

Braund KG. 1995. Laryngeal paralysis-polyneuropathy complex in young dalmatian dogs. In JD Bonagura and RW Kirk(eds.) Kirk's Current Veterinary Therapy XII Small Animal Practice p. 1136-1140. WB Saunders Co., Toronto.

Bjorling DE. 1995. Laryngeal paralysis. In JD Bonagura and RW Kirk(eds.) Kirk's Current Veterinary Therapy XII Small Animal Practice. p. 901-901. WB Saunders Co., Toronto.

brachycephalic syndrome

roblib — Sun, 02 May 2010 01:27:01 +0000

What is ... ?:

The full name of this disorder is brachycephalic airway obstruction syndrome (BAOS). Brachycephalics are those breeds which have a comparatively short head. Because of their anatomy, virtually all dogs of these breeds have some degree of increased work associated with breathing from the time they are born. Many have varying degrees of obstruction to their airways, which causes signs ranging from noisy breathing to collapse.

The most common anatomical features that lead to the respiratory difficulties typical of these breeds, include an elongated and fleshy soft palate, and narrowed nostrils. Many affected dogs also have changes to the larynx (everted laryngeal saccules) and a relatively small trachea (hypoplastic trachea).

How is ... inherited?:

Selection for exaggerated features has resulted in the respiratory difficulties in these breeds. For example breed standards for the English bulldog specify that the face should be very short, as should the distance between the tip of the nose and where it is set deep between the eyes. It is hardly surprising that this leaves little room for the structures involved in normal breathing.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Problems associated with this syndrome range in severity, with most brachycephalic dogs snuffling and snorting to some degree. Some will have no further difficulties, but many will have problems such as increasingly noisy breathing, coughing and gagging, fainting or collapsing episodes, and a decreased tolerance for exercise (ie. they tire easily). Over the long term, this also puts an increased strain on the heart. Some dogs, such as English bulldogs, may have frequent episodes of sleep-disordered breathing.

Overheating is especially dangerous in these breeds, because increased panting (the normal mechanism for cooling in dogs) can cause further swelling and narrowing of the already constricted airways, which will increase your dog's anxiety. Excitement, exercise, or warm weather (and especially a combination of these factors) can trigger this vicious cycle. These dogs can also have gastrointestinal problems, because of difficulties coordinating swallowing when they are working so hard at breathing. This can result in vomiting ar gagging because of swallowing so much air, or aspiration pneumonia, because of breathing in saliva or food particles.
All dogs of these breeds have an increased risk associated with sedation and anesthesia, for which your veterinarian will take extra precautions.

How is ... diagnosed?:

These problems are usually evident from a young age. If your dog has respiratory difficulties, your veterinarian may discuss this syndrome with you as part of a regular visit, or you may bring your dog in because of an episode such as collapsing after exercise.

Because some changes in anatomy are common to all dogs of these breeds, diagnosis is really a question of the degree of abnormality. The overlong soft palate is best examined under general anesthesia, and so, because of the associated risks, your vet will most likely ask your permission in advance to surgically correct it at the same time if necessary. Neutering can often be performed at the same time.

How is ... treated?:

Medical treatment (oxygen therapy, corticosteroids) can be used for short term relief of airway inflammation. Surgery is required where severe anatomic faults interfere with breathing. Most commonly this involves removal of some of the excess fleshy soft palate, and widening of air passages at the nostrils.

It is important to keep your dog from becoming overweight, as this will worsen his or her respiratory difficulties in the long run.
For the veterinarian: In mild episodes of obstruction, short-acting steroids, oxygen therapy, and cooling the dog while it calms down may be sufficient. Bear in mind that sedation without intubation will relax upper airway muscles and may increase obstruction, and that hyperthermia may develop in an oygen tent or cage and exacerbate the problem.
These dogs, particularly the English bulldog, have an increased risk of aspiration pneumonia following surgery to correct airway problems.

Breeding advice:

This syndrome is directly related to the conformation or standards for these breeds. Although so common as to be accepted as normal for brachycephalics, BAOS causes serious physical problems and discomfort for individual dogs. Breed improvement by breeding away from the extremes of conformation that cause these problems, is a challenge for responsible breeders.

Dogs with pronounced breathing difficulties or that have required surgery to correct airway obstruction, should not be used for breeding. These dogs should be neutered at the time surgical correction is performed.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Hendricks, JC. 1995. Recognition and treatment of congenital respiratory tract defects in brachycephalics. In JD Bonagura and RW Kirk (eds.) Kirk's Current Veterinary Therapy XII Small Animal Practice.p. 892-894. W.B. Saunders Co., Toronto.

hypoplastic trachea

roblib — Sun, 02 May 2010 01:29:31 +0000

What is ... ?:

In this congenital condition (ie dogs are born with it), there is abnormal growth of the rings of cartilage that make up the trachea, resulting in a narrowed airway. Hypoplastic trachea is seen most often in young brachycephalic dogs, and can occur as one component of brachycephalic syndrome. The condition may also occur at the same time as heart abnormalities. Brachycephalics are those breeds which have a comparatively short head.

The degree of tracheal narrowing ranges from mild to severe, as does the severity of clinical signs. Some dogs with this condition appear to outgrow it.

How is ... inherited?:

unknown

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Since this is a congenital condition (ie dogs are born with it), problems are usually noticed by 5 or 6 months of age. The kinds of signs you will see include noisy or laboured breathing, and coughing. Your pup may become ill with bronchopneumonia (moist cough, lethargy, fever).

Dogs with no abnormality other than a mild to moderately narrowed trachea may have no clinical problems; however hypoplastic trachea is frequently seen as one element of brachycephalic syndrome. Affected dogs have varying degrees of obstruction to their airways, which causes signs ranging from noisy breathing to collapse.

How is ... diagnosed?:

Your veterinarian may find this problem on routine physical examination, or because your dog has respiratory difficulties. S/he will take x-rays to determine the extent of the narrowing, taking into consideration that all bulldogs have relatively small tracheas.

How is ... treated?:

There is no specific treatment to correct the tracheal malformation. If your dog does not have heart disease or brachycephalic syndrome, the condition may never cause any clinical problems.

It is wise to maintain your dog at a healthy weight, as being overweight will worsen any respiratory difficulties. There may be occasional need for broncho-dilator therapy and antibiotics to treat an infection.

For the veterinarian:

On x-ray, the size of the tracheal lumen does not vary with the stage of the respiratory cycle as is seen with tracheal collapse.

Breeding advice:

Dogs with this condition should not be used for breeding.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Brayley, KA, Ettinger, SJ. 1995. Disorders of the trachea. In EJ Ettinger and EC Feldman(eds.) Texbook of Veterinary Internal Medicine, p. 754-766. W.B. Saunders Co., Toronto.

tracheal collapse

roblib — Sun, 02 May 2010 01:38:45 +0000

What is ... ?:

Tracheal collapse is a narrowing of the inner diameter of the trachea, that fluctuates with the stage of the respiratory cycle. The rings of the trachea (made of cartilage) lose their ability to maintain their shape, and collapse when the dog breathes, causing a harsh cough. Most often this disorder is seen in middle-aged toy and miniature breeds. Chronic respiratory infection, obesity, and heart disease can all contribute to the development of the condition, but it appears that there is also a congenital deficiency (ie. a dog is born with it) in the make-up of the trachea itself.

How is ... inherited?:

unknown

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Affected dogs typically have a harsh, dry "honking" cough, that is paroxysmal in nature and gradually becomes worse over time. The cough may be brought on by excitement, exercise, pressure on the trachea (such as is caused by pulling on a leash, or an enlarged heart), or drinking or eating.

How is ... diagnosed?:

Your veterinarian will suspect this problem if your small breed dog has a history of coughing "fits" that have gradually become worse, and if your dog responds to gentle pressure on his/her trachea with the typical "goose honk" cough. Your vet will do a thorough exam of the respiratory system and also the heart, because underlying heart disease is not uncommon in these dogs. Diagnosis and the degree of collapse are confirmed by comparing x-rays taken at the maximum inhalation and exhalation phases of the respiratory cycle. The trachea can also be examined during breathing by use of a scope, to determine the severity of the problem.

How is ... treated?:

Your veterinarian will discuss with you ways to manage this condition in your dog. Most cases can be treated successfully medically, with the use of bronchodilators, nebulizers or vaporizers, and occasional use of corticosteroids or sedatives as necessary to treat inflammation of the trachea. Your dog should be walked on a halter, rather than a collar.

For the veterinarian:

Either the cervical, or both cervical and thoracic trachea may be involved. If both, then inspiratory radiographs usually show collapse of the cervical and dilation of the thoracic segments, and essentially the reverse on expiration. Fluoroscopy may be necessary to confirm the diagnosis, as sometimes collapse is only evident during forced expiration of coughing.

Breeding advice:

Ideally, affected dogs should not be used for breeding. This is difficult in practice however, because many affected dogs do not develop signs of this condition until middle age, when they have already been bred. It is preferable not to use lines of dogs for breeding in which collapsing trachea is a problem.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Brayley, KA, Ettinger, SJ. 1995. Disorders of the trachea. In EJ Ettinger and EC Feldman(eds.) Texbook of Veterinary Internal Medicine, p. 754-766. W.B. Saunders Co., Toronto.