1. Overview

The word asthma originates from human medicine and refers to chronic airway inflammation involving a variety of cells, especially mast cells, eosinophils and T lymphocytes; in susceptible individuals, this inflammation can cause repeated attacks of wheezing, Symptoms such as shortness of breath, chest tightness, and cough often occur at night or in the early morning; such symptoms are often accompanied by widespread and variable expiratory flow velocity limitation, but can be partially relieved naturally or with treatment; such symptoms are also accompanied by shortness of breath The tract has increased reactivity to a variety of stimulating factors. But it should be remembered that a severe asthma crisis can occur at any time and can be life-threatening. Asthma with constricted airways can be classified as spontaneous or allergic. Treatment is based on reducing and preventing airway constriction.

The definition of feline asthma is difficult to pin down. We often call it chronic bronchitis, bronchial asthma or allergic bronchitis, etc. Most of them are caused by allergies and belong to the allergic reaction type. When cats are stimulated by allergens, 5-hydroxytryptamine present in platelets and mast cells is released, causing airway smooth muscle to contract. Symptoms usually gradually worsen, eventually leading to bronchiectasis and emphysema.

The main allergens that cause cat asthma include pollen, grass seeds, smoke, sprays (perfume, deodorant, hair spray, gel, etc.), cat litter dust, dry cleaning powder or food allergens. The difficulty is that these allergens are often not accurately diagnosed, and asthma symptoms persist and become more frequent. Although it can be well controlled with medication, airway problems may remain with the cat throughout his life.

At present, all clinical diagnostic standards for feline asthma are based on human standards, and veterinary clinical practice needs to be further improved. In terms of human asthma, we know the specific time of asthma attacks and the pathological process of the respiratory tract. However, when cats show symptoms of asthma, we are still unable to determine the specific attack time of asthma and the pathological changes in the trachea. So most of the research draws on research on human asthma.

2. Causes

Feline asthma is a hypersensitivity reaction to environmental allergens, and in most cases it is difficult to identify the specific source of irritation. The sources of asthma irritation can be divided into the following categories through clinical diagnosis and treatment records.

1. Smoke: candles, cigarettes, fireplaces, various incense sticks, outdoor burning

2. Perfume: perfume, air freshener, scented cat litter

3. Chemicals: new carpets, paints, furniture stains

4. Environmental factors: pollen, mold, damp and cold air

5. Dust: dust mites, Lingyan cat litter, bedding (especially when cleaning the house)

6. Stress: overwork, long-distance travel, pressure, fear (leading to shortness of breath and irregular heartbeat)

7. Microorganisms: Parasites, Mycoplasma

8. Overweight.

These reasons may irritate the airways and trigger asthma. Sometimes it's a single stimulus, but more often it's a mixture of multiple sources acting together. This is why clinical identification of the source of stimulation is difficult.

3. Pathophysiology

1. Uncertain stimulation sources cause chronic active infection, leading to the following results.

(1) Epithelial cells shed and proliferate.

(2) Goblet cell hypertrophy and hyperplasia.

(3) Submucus gland hypertrophy, hyperplasia, and excessive secretion.

(4) Edema and cell infiltration into mucosa and submucosal membranes.

(5) Smooth muscle hypertrophy (rare).

(6) Submucosal fibrosis (occasionally). [page]

2. Excitation of stimulating (cough) receptors produces cough and increases tracheobronchial mucus secretions.

3. Airway obstruction is due to intraluminal mucus, edema and cell infiltration accompanied by reversible smooth muscle contraction.

4. Collapse of the airway in the chest during exhalation, especially during exercise, excitement or coughing and for a period of time afterwards.

5. Feline asthma is an allergic reaction (type 1) allergy.

When the various stimulation sources mentioned above enter the body for the first time to cause an immune response, that is, under the action of APC and TH cells, IgE-producing B cells distributed in the lamina propria of the mucosa or local lymph nodes are stimulated, and the latter proliferate and differentiate to secrete IgE. Antibody. IgE binds to the Fc receptor (FcεR) on the surface of mast cells and eosinophils, sensitizing them and placing the body in a sensitized state. When the allergen enters the body again, it binds to specific IgE antibodies on the surface of mast cells and eosinophils. Mast cells and eosinophils are sensitized after binding to IgE. As long as two adjacent IgE molecules or surface IgE receptor molecules are cross-linked in the sensitized cells, the cells will be activated, degranulated, and release pharmacological agents. Active mediators of action, such as histamine, slow reactant A, serotonin, anaphylatoxins, leukotrienes and prostaglandins. These mediators can act on tracheal tissue, causing capillary dilation, increased permeability, mucosal edema, tracheospasm, tracheal obstruction, etc.

IV. Clinical symptoms

There is no obvious age or breed tendency for this disease, but Siamese cats are usually more susceptible and have the most severe attacks.

Affected cats may exhibit standard asthma symptoms, crouching into a hen position, extending their necks close to the ground, and then developing a rough wheezing sound (which can be detected by auscultation of the entire lungs). haveSymptoms of cough may also appear sometimes, mostly dry cough or cough with phlegm, and nausea at the end of the cough. Depending on the severity or frequency of allergens, some cats will have attacks continuously within a day, others will have attacks once every few days, and mild ones will only have attacks once every few months to years.

Because of the pathological changes in the airways of cats with asthma, the amount of air the cat exhales and inhales each time is much less than normal, and the exhalation time is significantly longer. Abdominal breathing with shallow and rapid breathing. Some cats even breathe with their mouths open to maximize air flow. In severe cases, cyanosis may occur.

Asthmatic cats may also experience symptoms such as exercise intolerance, decreased appetite, and depression. However, in the early stages of the disease, the cat may only show this respiratory condition at home, and be very quiet when it comes to the hospital. When encountering this situation, it is best to ask the animal owner to use a camera device to record the cat's wheezing and provide it to the doctor for differential diagnosis of the disease. This is a very useful diagnostic basis for the actual diagnosis of cat asthma.

5. Diagnosis

The actual clinical diagnosis of feline asthma mainly involves clinical history investigation, imaging and tracheal cytology examination. The investigation of clinical history is the most practical and effective method for currently clinically diagnosing feline asthma in pets. This part relies on the animal owner’s detailed description of the cat’s entire disease process. It is best to provide a video of the disease at home (the specific clinical symptoms are in described above).

Chest X-ray characteristically shows clear bronchial vascular texture. Bronchial mucosal hyperplasia and cellular infiltration cause bronchial thickening, which appears as a ring-shaped image on chest X-ray. The gradual increase of inflammatory exudate and mucus in the bronchioles causes the tracheal wall to appear more obvious on images. In some severe cases, pulmonary edema or emphysema may occur.

The small airways constrict so that gas cannot be expelled normally. Overinflation of the lungs, making them appear much larger than normal. This excessive expansion causes the diaphragm to become flatter. As the cat tries to breathe through its mouth and inhales a large amount of air, the stomach will become overly distended and inflated.

(Above) Ventodorsal X-ray of a domestic shorthair cat with severe bronchopneumonia and emphysema showing air trapping. This image was taken using horizontal X-beam technology while the cat was resting on its right side. The dependent lung area is hyperinflated and the heart (H) is close to the upper chest wall. There is a soft tissue mass (M) lesion on the caudal midline, which represents an area of ​​lung consolidation. (Bottom) Lateral radiograph of the same cat demonstrating extensive pulmonary hyperdistension and dorsal lung consolidation.

However, the prerequisite for imaging diagnosis is not to aggravate the cat’s pain. Because in some serious cases, any movement or improper restraint can endanger the cat's life.

(Above) Signs of generalized bronchointerstitial lung disease in a 5-year-old domestic shorthair cat with allergic bronchitis. Due to reticular interstitial lesions, the lungs have a "chicken claw" appearance, and a small amount of bronchial texture can also be seen. (Bottom) Close-up of the caudoventral lung fields of the same cat.

However, the X-rays of some cats with asthma do not show the above abnormalities. Because if there are no obvious asthma symptoms, X-rays are difficult to show abnormalities. In fact, the diagnosis of asthma is very complicated, and clinicians often ignore the possibility of asthma because there are no abnormalities in the X-ray data.

Tracheal cytology mainly reveals granulocytic infiltration, especially eosinophilia, and sometimes alveolar macrophages, but few inflammatory cells and no signs of infection. Due to the high recovery rate of epithelial cells, it is recommended to use tracheal wash fluid to obtain cytology samples, and the use of cytology brushes is not recommended.

Samples obtained by tracheal washing can also be cultured for secretions, and generally more aerobic bacteria can be obtained than endoscopy. Bacterial cultures do not need to be passaged in nutrient-rich media to indicate the true pathogen.

Researchers in the United States reported that when a large number of eosinophils are found, it can be used as a reference diagnostic material for cat asthma. But it still cannot be determined that a cat has asthma based on this alone. Sometimes there is a certain amount of eosinophils in the tracheal secretions of normal cats. In addition, parasitic infections such as heartworms can also increase the body's eosinophil content. The possible influence of these diseases must first be ruled out through other diagnostic methods. Abnormal blood pictures and serum chemical reactions represent some unrelated diseases and have little diagnostic significance for asthma.

To sum up, when clinicians deal with suspected cases of feline asthma, they must ask the animal owners in detail to fully understand the cat's condition. The results of impact studies and laboratory tests are also combined. Eventually an accurate diagnosis was obtained. And do a good job of returning visits and following up on the cases.

6. Differential diagnosis

Because there are many clinical diseases that can cause cats to cough and have shortness of breath, differential diagnosis must be carried out to investigate and ultimately diagnose the disease. The diseases to be identified are roughly as follows.

1. Heart failure. It often causes cardiogenic tachypnea and cardiogenic pulmonary edema.

2. Heartworm. A large number of parasites inhabit the cardiovascular system, which can block blood circulation and lead to heart failure and cardiogenic diseases.

3. Pneumonia. Simple severe pneumonia can also cause coughing and shortness of breath in cats. But it rarely relapses after cure.

4. Leukemia and feline AIDS. Impaired immune function can lead to various allergic reactions.

5. Foreign objects. Foreign objects blocking the airway can cause severe abdominal breathing and shortness of breath.

Routine examinations are to eliminate these interfering factors, so although only imaging and cytology are the most important for asthmadiagnostic significance, but other examinations must also be done.

7. Treatment

Treatment varies depending on the stage of asthma. Cats with a history of coughing can be treated conservatively while cats with difficulty breathing cannot. An important factor in dealing with a cat that has difficulty breathing is to avoid further harm to the cat. This can be done by stabilizing the cat in an oxygen cage and further observing the breathing pattern.

1. Emergency treatment includes oxygenation and rapid bronchodilation, the latter of which can use rapid-acting corticosteroids, sympathomimetics, and bronchodilators.

(1) Quick-acting corticosteroids such as prednisone sodium succinate (1~4mg/kg iv) or glucocorticoids. This is important in the first aid management of feline asthma.

(2) Epinephrine is a fast adrenergic agonist that can rapidly dilate the bronchi of critically ill patients. [page]

2. The key to asthma is long-term control treatment

It is important to realize that the fundamental problem of asthma is inflammation of the trachea, which is caused by constriction of the trachea. To address inflammation, corticosteroids have been the cornerstone of treatment. These drugs can be given by mouth, injection, or aerosol inhalation. At the beginning of treatment, either by mouth or by injection. This type of drug is relatively cheap and can achieve good results, and can also provide useful therapeutic diagnostic data for determining later treatment plans. If oral corticosteroids are effective initially, long-term continued use is generally recommended. But long-term use of corticosteroids will definitely have certain side effects, even if cats are highly resistant to corticosteroids. For a cat with severe asthma symptoms, oral medication may be difficult, and long-acting steroid injections may be an option to control symptoms. However, since injectable drugs are more effective than oral drugs, all side effects will be stronger than oral drugs. This means that injectable drugs can only be given periodically to avoid the risk of metabolic diseases such as diabetes. If a cat requires multiple injections of medication over the course of a month, an inhaler should be considered (see below for details).

The key to using oral corticosteroids is to find the lowest controlled dose over time. Cats may become resistant to steroids if high doses are required for frequent use. At this time, you also need to consider changing to a different drug or a different method of administration.

(1) The initial dose of prednisolone is 1 mg/kg, po, bid, 10~14 days;

(2) Maintenance dose 0.1~0.25mg/kg, po, bid, once every other day or the lowest effective dose to control cough;

(3) Corticosteroid treatment should gradually reduce the dosage within 2 to 3 months.

3. Other treatment options besides corticosteroids

(1) Antibiotics should be used when bacterial infection is confirmed by bacterial culture, and preventive or long-term antibiotic treatment should be avoided.

① There is no evidence that bacterial infection plays a major role in chronic bronchitis in cats.

② Antibiotic treatment is determined based on the bacterial culture results. The choice of antibiotics is the same as for other respiratory tract inflammations.

(2) Cough medicine is only used when animals faint after coughing or cannot sleep due to coughing, or when livestock owners cannot sleep due to animal coughing.

① Butorphanol 0.05~0.1mg/kg, po, sq, sid~tid.

② Hydrocodone (bitartrate) 0.22mg/kg, po, sid~tid.

(3) Bronchodilator drugs.

Bricanil and theophylline are ideal bronchodilators and are often used to deal with airway narrowing in asthma. If tracheal stenosis is a major problem in a sick cat, applying this drug can be of great help. Both terbutaline and theophylline can be taken orally or injected. It is recommended that the owners of sick cats keep some at home for use in emergencies. The doctor should inform the owner of the correct medication method and teach the owner how to administer it.

① Bricanil 0.625mg/cat, po, bid.

② Aminophylline 4~6mg/kg, po, sid.

(4) Antihistamines

Histamine is an inflammatory substance released during allergic reactions. Histamine has long been thought to be involved in airway constriction mechanisms, and antihistamines are widely prescribed for feline asthma. But recent research has shown that there is a receptor called H3 in the cat's airway, which produces a swelling response instead of a contraction response when it senses histamine. This is why sometimes antihistamines don't have the desired effect. Antihistamines are generally ineffective in treating cat asthma.

(5) Cyclosporine[page]

The use of cyclosporine in the treatment of asthma is relatively new. It is often used as an immunomodulator in human organ transplant surgeries. It is occasionally given with other medications when inflammation cannot be controlled with medications alone. Or when the cat cannot take steroids for some reason (complicated diabetes, history of calcium oxalate stones, etc.), cyclosporine can be used.

4. Inhaler treatment

Just like asthma in humans, asthma in cats can also be controlled with an inhaler. In order for cats to use inhalants successfully, special equipment is required. Some veterinarians use children's asthma inhalers with medical masks, but the results are not ideal. An asthma inhaler (AEROKET) specifically for cats is currently available.

The inhaled drugs are mainly steroids and trachealAs dilation drugs, you can choose human inhaled drugs, such as Flixotide and Serevent. Inhaled drugs are limited to the respiratory system and do not cause serious side effects like oral or injected drugs.

Serevent is a long-acting β2 antagonist. It begins to take effect 15 to 30 minutes after inhalation, but the effect can last for more than 12 hours. This agent is not recommended for use in acute bronchoconstriction, but it can be used with When used daily, steroid inhalers can reduce the dosage of steroids and relieve and control asthma symptoms.

Flixotide is considered to be the most effective and longest-acting inhaled steroid inhaler. Steroid inhalers are the most effective anti-inflammatory inhalants. When used during the onset of asthma, they can help control asthma symptoms and normalize lung function. , and prevent irreversible airway damage, it can help within 24 hours after inhalation, but to achieve the best control effect, it may need to be used continuously for 1 to 2 weeks or longer; when the drug is stopped, the effect on asthma The control effect can last for several days.

8. Prognosis and monitoring

For cats with asthma, try to reduce airborne irritants. Don’t make the area where cats live filled with smoke, and try to use dust-free cat litter. If you need to get rid of pests, try not to use spray pesticides. Consider using an air purifier in your home to maintain ventilation. Controlling your weight and losing weight can also slow asthma symptoms. For food, you can choose hypoallergenic prescription recipes.

Tell cat owners that once their cat develops abdominal breathing and mouth breathing, they must seek medical attention as soon as possible. The owner should explain that the treatment of cat asthma is only to do everything possible to improve the quality of life of the cat, but it is impossible to completely cure it. Although the coughing frequency decreases over a period of time, it is rarely completely eliminated. Exercise intolerance will increase, and the degree of collapse of the airway within the tracheal lumen can be seen through bronchoscopy. Weight reduction in obese animals can improve exercise tolerance and improve oxygen tension. Re-evaluate the animal's physical condition and medication every 3-6 months. If coughing increases in severity or frequency, exercise tolerance decreases, or the animal develops systemic disease, the animal's status will need to be reassessed.