Asthma (chronic bronchitis)

Introduction
Normal Physiology
Abnormal Physiology
Cause
Symptoms
Diagnosis
Treatment

Introduction

Asthma is a problem we tend to see much more often in cats than dogs, with the siamese cat being the most prevalent breed. Anyone who has ever had an asthmatic attack has an idea of what these cats go through when they can't get their breath. Its like trying to breathe with a pillow pressed against your nose and mouth.

This disease goes by several names- feline bronchial disease, allergic bronchitis, and allergic airway disease.

A glossary of medical terms will be used in this page:

Normal Physiology

In the normal thorax inhaled air is brought to the lungs through progressively smaller breathing passages. It starts with the trachea (windpipe) and progresses to bronchi and bronchioles, eventually ending at the actual lung tissue called alveoli. It is at the alveoli that oxygen is absorbed by red blood cells on inhalation and carbon dixode is excreted on exhalation.

These breathing passages contain smooth muscle that controls their size. This is the type of muscle that works automatically without you consciously telling it what to do. When these muscles are relaxed the air passages and lung tissue are fully open and breathing is effortless. When they contract (called constriction) the airways narrow dramatically and it is difficult for air to make it all the way to the lung tissue where it exchanges oxygen for carbon dioxide. The size of these breathing passages, especially the bronchioles since they are small in diameter, can have a substantial influence on how much air makes it all the way to the alveoli.

These are the lungs taken during a necropsy. The lungs are sponge-like and have an extensive blood suppy. You can see just a small portion of the blood supply- it is the three vertical and bluish vessels going from the heart to the lungs at the bottom of the picture. Within the actual spongey lungs there is an extensive network of small blood vessels.

The lungs have an extensive network of passages and blood vessels. This barium radiograph illustrates just some of those breathing passages. The barium outlines the major bronchi, the 4 large white breathing passages below. All the fainter whitish area in the lungs below are barium in the small bronchi and alveoli. You can see how extensive this network is.


Since we are an exotics practice, we thought it might be fun to show you the air filled lungs of a bearded dragon. The heart is the purplish and round structure to the upper left of the picture. The lung is the air filled and mesh appearing structure in the middle of the picture.




The lungs are very sensitive and easily damaged. The dark areas on this lung were caused by trauma- this pet was hit by a car. This is called a pulmonary contusion

Pathophysiology

Something (smoke, pollen, perfume) stimulates the bronchi and bronchioles, causing them to become inflamed and swell (edema). This sets up a hypersensitivy reaction causing the smooth muscle in them to constrict.   Sometimes the smooth muscle hypertrophies (gets larger) and causes long term problems.

As the smooth muscle in the bronchi and bronchioles constrict  breathing becomes harder. In addition, cells that normally produce mucous in small quantities might increase their production and literally clog up the air passages. If enough mucous production and constriction occurs the alveoli are unable to exchange oxygen and carbon dioxide to the red blood cells. Obviously, this is a serious problem because you cat can no longer exchange oxygen and carbon dioxide at the alveoli.

A type of white blood cell called eosinophils starts releasing chemicals known as mediators. These chemicals cause scarring of the breathing passage adding to the problem.

Unfortunately, chronic asthma can increase the blood pressure (hypertension) in the lungs leading to potential failure of the right side of the heart. It can also progress and cause emphysema.

Cause

In most cases we do not know the cause, which of course is frustrating. Risk factors include cigarette smoke, marijuana smoke, dusty cat litter, air or scented fresheners, and any aerosol-like deodorant or hair spray.

 Litter that is scented, is dusty or finely ground and has clay in it can be a problem. Some cats get the problem when exposed to litter made from pine or cedar, especially if they have been treated.  Sometimes litter that is made from newspaper, corn, wheat, or wood pellets can be helpful.  Clean the litter pan more often to prevent noxious odors.

Tobacco and marijuana smoke are very toxic to animals. In additon to predisposing dogs and cats to respiratory disease in general, this smoke is a potent stimulator of asthma in cats. Even the smoke that lingers on your clothes and breath can cause a problem, so smoking elsewhere does not prevent this problem. Scented candles and the burned wood in your fireplace are also implicated.

Our households are drowning in a world of chemicals. These chemicals can trigger and allergic reaction. This includes cleaning products, fabric softeners, carpet cleaners and air fresheners, shampoo and soap, hair dye, baby powder, furniture polish, paint, perfume and cologne- you get the picture.

A type of allergy, called allergic inhalant dermatitis, is caused by grasses, trees, shrubs, pollen particles, house dust molds, bed bugs and mites. These same allergens can set off an asthmatic attack.

Food allergies can also be a significant factor with asthma and skin conditions in cats. The allergy can be due to the beef, fish, corn, milk, wheat, or gluten that is in many foods. Even foods that have not caused a problem in the past can trigger an allergic reaction some time in the future. One of the foods we have found most beneficial when we suspect a food allergy is Hills Z/D or Ultra. It must be fed for up to two months to see if it is working. To confirm the food allergy you need to feed the original food and see if the asthmatic or skin problem recurs.

Stress can add to the probem. Cats do not like abrupt change in their daily routine, so take it slow whenever you make a change. Children, guests, repairmen, gardeners, maids, etc can all be a source of stress that adds to the problem. Diseases like diabetes mellitus and kidney disease can add chronic stress, especially when giving insulin injections or SQ fluids.

Symptoms

Symptoms of asthma can be chronic, acute, or intermittent. The classic signs of a cat with asthma are wheezing or coughing. If you are observant you might have noticed an slight increase in your cats respiratory rate or effort prior to the wheezing or coughing. Other symptoms are sneezing and labored breathing. As time progresses you might even observe a poor appetite (anorexia), weight loss, or lethargy, although these are not common symptoms.

The wheezing or coughing can vary in severity. Your cat might extend its neck or even breathe with an open mouth when severe. If mild all you might notice is an increased respiratory rate when your cat is at rest.

Diagnosis

Cats are masters at hiding problems, so by the time a diagnosis of asthma is made the disease process has usually been present for a significant period of time. This emphasizes the importance of close observation of your cat and a physical exam if you suspect a problem.

Numerous other diseases cause similar symptoms, so the diagnostic process should help differentiate them. Some of these diseases that have similar symptoms include:

    Heartworm
    Pulmonary contusion
    Diaphragmatic hernia
    Pleural effusion
    Chylothorax
    Lung worms
    Heart disease
    Cancer
    Heart failure (cardiomyopathy)
    Pneumonia

Signalment

Mostly cats, with Siamese cats being the most prevalent breed. Most of these cats are young to middle aged.

History

The classic signs of wheezing and coughing, for a variable period of time prior to exam. Sometimes these cats cough in a crouched position while extending their necks. Other diseases like lungworms, heartworms, heart failure, foreign bodies, tumors in the lungs and fluid in the thorax can all cause coughing in cats. Asthma is the most common cause of coughing though in the cat.

Physical Examination

The findings of the physical exam depend on how severe the asthma is, how long it has been present, what caused it, and if there are any other disease processes occurring simultaneously.

The trachea (windpipe) might be sensitive and elicit a cough upon palpation. An increased respiratory rate might be noted, along with increased lung sounds on auscultation with the stethoscope. The lungs sounds might be crackles or wheezes. There might even be normal lungs sounds in the presence of asthma.

More expiratory effort vs inspiratory effort might be noted. This could even include an abdominal push. Heart rate can be low (bradycardia), normal, or high (tachycardia).

In severe cases there might be open mouth breathing and blue discoloration of the mucous membranes (cyanosis). Cyanosis is a serious sign and needs immediate attention.

Diagnostic Tests

A blood panel might show an increase in a white blood cell called eosinophil. This is not a consistent finding though.

This is what a typical CBC reports. This cat has elevated eosinophils as can be seen in the underlined areas. The top underlined area shows 22% eosinophils when up to 12% is normal. The bottom underlined area shows 4906 eosinophils per cc when the maximum should be 1500.  Sometimes this is a sign of parasites or asthma, sometimes there is no significance to it.

Radiographs are an important tool in diagnosis, although a normal radiograph is not uncommon even if your cat has asthma.

This is a normal chest radiograph in a cat. All the dark areas are lung or windpipe. They are dark because they are filled with air. This is what we want to see. The picture below labels the organs.

The anatomy is labeled for better understanding
T- trachea (windpipe)
L- lung
A- aorta
H- heart
B- Main bronchi

This is a typical radiograph of a cat with asthma. Notice how the lung is not as dark, and has a a moth eaten appearance. This is feline asthma.

This cat has asthma also, but the radiograph is not typical. The arrow point to the lesion in the lungs.

A different view of the radiograph you see above. You can see the problem area in the lungs at the arrow.

We cannot assume that just because a cat is breathing hard it has asthma.
This is what fluid looks like in the thoracic cavity. Notice how little dark lung there is. There are several different causes of this- they include diaphragmatic hernia, heart disease, pleural effusion, FIP, pyothorax and chylorthorax to name some of the more common ones.

Some of the fluid was drained from this thorax. In this case it is called chylorthorax. You can tell by the milky fluid in the syringe.

After draining the dark lung tissue becomes more apparent. There is still a substantial problem, but at least now the lung can expand and the cat can get some air.

Bronchial wash is a secondary diagnostic test.  For this test a small amount of saline is flushed into your cats trachea (windpipe). This saline is retrieved and analyzed for cell type. An excess of a type of white blood cell called an eosinophil could indicate asthma. Eosinophils can also be found in normal cats, so this is not a perfect test.

In addition to analyzing the cells a culture and sensitivy can be performed to look for pathogenic bacteria. It is common to grow bacteria in this culture, so this test is not always helpful. If the bacteria are grown in large amounts, or if a Mycoplasma is present, we will sometimes treat with antibiotics.

Heartworm antibody and antigen tests can also be used to eliminate the possibility of feline heartworm disease.

Fecal exam to check for internal parasites.

Treatment

    100% oxygen

Cats that are having a severe breathing problem, called dyspnea, are placed in 100% oxygen. This calms them down and allows them to get the oxygen they are starving for. We usually do this before we proceed with any diagnostics or treatment.

This movie shows a dyspneic cat in the initial stages of its oxygen therapy. Click on it to view.

Summary

Most cats with ashtma are kept well controlled with medication. Be on the alert for subtle breathing patterns that signal the problem could become acute. This needs immediate attention by us. Try to keep stress to a minimum, and make sure your pet is not overweight. This is an all too common problem, and predisposes your pet to other problems besides asthma.

For most cats the prognosis is good for the long term if caught early enough and medication is used consistently.