consultant on call RESPIRATORY MEDICINE

Feline and Bronchitis Philip Padrid,RN,DVM,Family Pet Animal Hospital,Chicago,Illinois,and Ohio State University & University of Chicago

Profile GEOGRAPHIC DISTRIBUTION asthma,” results from a complex interplay None recognized. of activated T lymphocytes, antigen, anti- gen-processing cells, various cytokine pro- DEFINITION teins and chemical messengers, and activat- Chronic bronchitis and asthma are both SIGNALMENT Siamese and Siamese-related breeds appear ed eosinophils and other inflammatory cells chronic inflammatory diseases that occur in to be at risk. Cats of any age may develop in the bronchial mucosa. The inflammatory the lower airways (bronchi and bronchioles). chronic bronchial disease, although young results of these processes include excessive In practice, it is often difficult to distinguish and middle-aged cats (1 to 8 years) most secretion, airway wall edema, and, in between the two disorders. Chronic bronchi- commonly have the disorder. Male and asthmatic patients, bronchoconstriction. tis is defined in part by the presence of a female cats appear to be equally at risk. Airway muscle hypertrophy and hyperplasia daily cough; asthma is defined in part by are more common in asthmatic than in acute bronchoconstriction that may resolve bronchitic airways. Basement membrane spontaneously or with treatment. CAUSES thickening is a feature of asthma in humans Bronchoconstriction may or may not cause Unknown. The causes of asthma and bron- but has not consistently been found in cats. cough in an individual cat (known as cough- chitis probably differ. The most common causes of asthma in humans include house variant asthma). Thus, cats with a daily SIGNS cough may have either disorder, while cats dust mites, feline “dander,” and cockroach- Cough, mucus production, wheeze, open- without cough may have asthma but do not es; chronic bronchitis is the result of ciga- mouth breathing, and exercise intolerance have chronic bronchitis. Both disorders may rette smoke in humans, although this directly resulting from the pathophysiologic result in wheeze and exercise intolerance. association has not been shown in cats. derangements described above. Finally, human asthma is a syndrome in RISK FACTORS which the causes may vary greatly, including HISTORY allergy, exercise, and cold air, in individual Unknown. In humans with asthma, there is Cough and increased respiratory rate and patients. For purposes of this discussion, a 50% chance of developing asthma if both effort are common to asthma and chronic asthma in cats refers to allergic asthma. parents are asthmatic. Living indoors or out- doors is not causally associated with devel- bronchitis. There is usually a gag/choke or swallow at the end of the cough, signifying GENETIC IMPLICATIONS opment of chronic bronchitis or asthma in excess mucus production. Asthmatic Several “asthma genes” have been implicat- cats. Cigarette smoke increases symptoms in patients may have symptom-free periods, ed in the pathophysiology of human asth- human patients with established disease; whereas a daily cough is the defining fea- ma, and this is also an active area of passive cigarette smoke has been linked to ture of bronchitis. research in veterinary medicine. The Siamese bronchial disease in children. No data con- breed seems to be overrepresented, sug- firm this phenomenon in cats, although gesting an inherited trait. common sense suggests that exposure to cigarette smoke is probably harmful. Diagnosis INCIDENCE/PREVALENCE There are no precise actuarial data. Chronic PATHOPHYSIOLOGY PHYSICAL EXAMINATION bronchial disease (both bronchitis and asth- Unknown. In humans, cigarette smoke caus- Physical examination may be unremarkable. ma) probably affects 0.75% to 1% of the es cough, airway wall thickening, and hyper- Most cats with chronic bronchitis or asthma feline population in general and may affect trophy of the mucus-secreting apparatus. have increased bronchovesicular 5% of the Siamese breed. Asthma is more complex and is better sounds heard diffusely. Wheeze may be thought of as a “syndrome” with many heard, especially during expiration. causes. The most common form, “allergic continues

consultant on call ...... NAVC clinician’s brief.....october.2005.....37 consultant on call C ONTINUED

Respiratory rate may be increased, and tis is peribronchial cuffing, often described Bronchoscopy is usually not necessary for there may be nasal flaring. Cyanosis occurs as doughnuts or tram lines (Figure 1). diagnosis. Pulmonary function testing is in severe cases. Other common causes of cough and used to determine airway hyperresponsive- increased respiratory effort include pneumo- ness in asthmatic persons. This technology is DIAGNOSIS/DIFFERENTIAL DIAGNOSIS nia, , cancer, and heartworm dis- now available to approximate airway reac- There are no clinical signs or laboratory ease. These disorders usually create radi- tivity in awake, nonrestrained cats (Buxco tests available in general practice that are ographic abnormalities that differ from the box, Buxco Electronics; Wilmington, NC). pathognomonic for asthma or bronchitis. We classic findings of hyperinflation and pursue diagnostic testing in cats with bronchial markings seen in chronic bronchi- Skin testing for the presence of antigen- cough, tachypnea, and/or wheeze to deter- tis or asthma. specific IgE has been proposed as a way to mine the presence of other common causes determine an underlying “cause” of allergic of these signs—for example, heart failure, Both bronchitic and asthmatic cats have asthma. However, the biological response of , pulmonary cancer, respiratory excessive airway mucus. Nonseptic neu- mast cells in skin often differs from that of parasitism, and inhaled foreign bodies. trophils are the predominant cell type in mast cells in the airways to the same anti- bronchial fluid. Eosinophils may predomi- gen in the same cat. For this reason, the LABORATORY FINDINGS/IMAGING nate in bronchial fluid from asthmatic cats, author does not yet recommend this manner Asthmatic cats often present with a history although healthy cats also frequently harbor of testing. of sudden onset of labored breathing that is large numbers of eosinophils in the respira- quickly relieved with some combination of tory tract. POSTMORTEM FINDINGS oxygen, bronchodilators, and steroids. In • Bronchitic and asthmatic airway epitheli- some cases, the only sign is chronic or inter- We also measure pulse oximetry in cats um may thicken (hypertrophy), evolve to a mittent cough. Patients with chronic bron- breathing room air to determine the relative different structure (metaplasia), or simply chitis have a history of chronic daily cough degree of impaired oxygen exchange. In become damaged (erosion or ulceration). with gag/choke or swallow at the comple- general, a pulse oximeter reading of 95% or • Bronchitic and asthmatic goblet cells and

tion of the cough, representing excessive above (PaO2 of approximately 80 mm Hg or submucosal glands may enlarge and pro- mucus secretion. above) is considered stable; a reading of duce excessive amounts of a particularly

90% or below (PaO2 of approximately 60 thick form of mucus. The most common radiographic change mm Hg or below) is considered extremely • Asthmatic bronchial smooth muscle will common to both feline asthma and bronchi- unstable. often spasm and may undergo hypertro- phy and/or hyperplasia.

These changes are associated with cellular infiltration of the bronchial mucosa and sub- mucosa. This tissue may also become ede- matous. See Figures 2 and 3.

Treatment

INPATIENT OR OUTPATIENT Asthmatic and bronchitic patients may pres- ent in various stages of distress. The deci- sion to hospitalize these patients is made on a case-by-case basis. In addition to clinical criteria, patients with a pulse oximeter read- 1 ing of 95% or higher are often treated as outpatients; those with readings of 90% or This lateral thoracic radiograph demonstrates classic features of feline asthma, including hyperinflation and peribronchial infiltration (doughnuts and tram lines). MDI = metered-dose inhaler

38....october.2005.....NAVC clinician’s brief ...... consultant on call

Prednisone is gradually tapered over a 2- week period to allow the inhaled medica- tion to achieve its full effect.

Bronchodilators Albuterol is given by inhalation as needed in the same manner as steroids. Albuterol can be given every one-half hour for 4 to 6 2 3 hours if needed in a crisis. Oral drugs can be used for cats that cannot tolerate inhaled A cross section from the large airway of a cat This large airway from a cat with chronic bronchitis with asthma, demonstrating the classic findings of demonstrates goblet cell hypertrophy and a mucus albuterol. The pharmacokinetics of theo- smooth muscle hypertrophy, invagination of plug. Airway smooth muscle is normal and there is phylline are well described in the feline epithelium (bronchoconstriction), and luminal exu- no evidence of bronchoconstriction, thus distinguish- species; however, in the author’s experience, date. ing bronchitis from asthma. the response to terbutaline (0.1 mg/kg PO Q 12 H) is more consistent. Cats in status asth- below are frequently hospitalized and treat- and the medication fills the spacer. The cat maticus can also be treated with parenteral ed with oxygen. Between the 90% and 95% breathes in and out 7 to 10 times with the terbutaline (0.01 mg/kg IV or IM). values, there is great room for individual mask in place, and treatment is complete. clinician decision making. MEDICATIONS Oxygen ACTIVITY To some extent, drug therapy depends on Oxygen is usually given in an oxygen- Cats with bronchitis or asthma usually whether clinical signs occur daily. Because enriched cage. The author uses the patient’s adjust activity to suit their level of comfort. chronic bronchitis is defined in part by the clinical status and pulse oximeter reading to presence of a daily cough, we treat bron- determine the need for oxygen (pulse CLIENT EDUCATION chitic cats with a twice-daily corticosteroid. oximeter reading > 95% approximates a Both chronic bronchitis and asthma are Asthmatic cats are slightly more complex. PaO2 of 80 mm Hg and does not usually chronic disorders that require chronic treat- Cats that have clinical signs more than require oxygen therapy). ment. Some patients with asthma outgrow twice weekly are treated with daily corticos- the disease, and others seldom have clinical teroids; those that have clinical signs less Antibiotics signs. Some cats with asthma get worse, than twice weekly are usually treated with There is no objective evidence that bacterial some get better, and others remain stable just bronchodilators on an as-needed basis. infection plays a significant role in the cause for years. Cats with chronic bronchitis tend This approach is based on the National or continuation of most cases of feline asth- to slowly deteriorate and become less stable Institute of Health’s recommendation for ma or chronic bronchitis. In general, antibi- as time passes. These patients rarely if ever humans with asthma and has served as the otics are rarely indicated for cats with asth- “grow out” of the disease. basis for treatment of more than 125 cats ma or chronic bronchitis and are appropriate with bronchial disease in the author’s prac- only when there is good evidence of true If inhalants are used, clients must be shown tice over the past 6 years. airway infection. how to use them with their own cat and demonstrate to the clinician to confirm that Corticosteroids Antileukotriene (or Receptor) Inhibitors they can use the medications correctly. Thus, Prednisone can be given at 1 mg/kg Q 12 H These drugs block production or ligation of the MDI is used with a “spacer” and face- for 5 days. The response is usually dramatic. leukotrienes (LTs) to their receptors. The mask that is specifically designed for cats. The drug is then tapered to the lowest effec- product of LTC4 and LTD4 metabolism, LTE4, The spacer is a plastic chamber the size of tive dose. If daily prednisone is required to is a useful marker for the production of the cardboard tube in a roll of toilet paper. control clinical signs, the author introduces these molecules in humans with asthma. The MDI fits into one end of the spacer; the Flovent (GlaxoSmithKline) (inhaled fluticas- Recent data suggest that LTE4 in urine, and other end attaches to the facemask. one, 110 µg Q 12 H), given as a single thus LTC4 and LTD4 in the bloodstream and “puff” into a feline-specific chamber airways, is not increased in cats with experi- The client places the facemask gently over (Aerokat, Trudell Medical International). The mentally induced allergic airway disease or the cat’s nose. The MDI is actuated (pressed), patient then takes 7 to 10 breaths. continues

consultant on call ...... NAVC clinician’s brief.....october.2005.....39 consultant on call C ONTINUED

Untreated asthma can be rapidly fatal. at a glance Untreated chronic bronchitis often gets worse and may result in chronic debilitation. • Asthmatic patients with a pulse oximeter reading of 95% or higher are often treated as outpatients; those with readings of 90% or below are frequently AT-HOME TREATMENT hospitalized and treated with oxygen. Aerosolized particles and dry, unhumidified • Bronchitic cats are treated with a twice-daily corticosteroid. air may contribute to clinical signs. • Asthmatic cats that have clinical signs more than twice weekly are treated with Humidification of room air to at least 40% daily corticosteroids; those that have clinical signs less than twice weekly are is recommended. Air purifiers are probably usually treated with just bronchodilators on an as-needed basis. only helpful if they are effective for the size • Prednisone and albuterol can be administered by inhalation with use of a of the room (or the house) where the cat spacer and facemask in asthmatic cats; the response to prednisone is often spends most of its time. Common sense dic- dramatic. tates that cats with bronchial disease should not be exposed to dust, molds, cigarette naturally occurring bronchitis. In addition, ther drug has lived up to its promise in a smoke, fireplace exhaust, construction

direct instillation of LTC4 into the airways of clinical setting. debris, carpet sweepings, and other particu- normal cats has no adverse effect on feline late matter. airway structure or function. No current data NUTRITION support the use of antileukotriene drugs to No dietary changes reliably benefit cats with FUTURE FOLLOW-UP treat cats with asthma or chronic bronchitis. asthma or chronic bronchitis. Grossly obese Stable cats should be reevaluated every 3 to patients will benefit from weight reduction 6 months. Unstable patients should be eval- CONTRAINDICATIONS & so that the diaphragm can fully expand dur- uated as often as needed until they become INTERACTIONS ing inhalation. stable. If bronchodilator drugs that increase beta- adrenergic tone increase myocardial con- tractility, cats with hypertrophic cardiomy- Follow-up In General opathy may theoretically have a worsening of their outflow tract obstruction. However, in practice this occurrence is rare. PATIENT MONITORING RELATIVE COST Patients with newly diagnosed chronic bron- $$–$$$ Initial evaluation and diagnosis Because inhaled steroids are not absorbed chitis or asthma should be rechecked within $–$$ Initial treatment into systemic circulation, they do not inter- 7 to 10 days to ensure that medications are $ Monthly medication being dispensed properly. act significantly with other drugs. As a Cost Key result, they are rarely contraindicated by other treatments or comorbid diseases. PREVENTION $ = < $100 $$$$ = $500-1000 There are no recognized common triggers of $$ = $100-250 $$$$$ = > $1000 asthma or chronic bronchitis in cats. PRECAUTIONS $$$ = $250-500 Asthma can be acute and life-threatening. Anything that can be inhaled can theoreti- Bronchitic or asthmatic patients should be cally trigger an asthmatic or bronchitic seen immediately if clinical signs worsen. cough. PROGNOSIS Asthma and chronic bronchitis are not cur- ALTERNATIVE & NOVEL THERAPIES COMPLICATIONS/COURSE able. Spontaneous resolution is common in No alternative therapies reliably benefit cats In some cats (15% to 25%), the right middle adult humans who developed asthma in with asthma or chronic bronchitis. lung lobe collapses. Although this may cause childhood. This may or may not be true in Experimentally, cyproheptadine was shown no additional clinical signs, it can be an asthmatic cats. Some cats with asthma or to block allergen-induced airway smooth- additional cause of chronic cough. The col- bronchitis may be only mildly symptomatic, muscle contraction in feline tissue baths and lapsed lung lobe reexpands in fewer than and others may have life-threatening illness. cyclosporine was used to inhibit the devel- 50% of cases. Education is critical so that our clients opment of airway reactivity. However, nei- develop realistic expectations of the effec- tiveness of drug therapy for their pets. ■

40....october.2005.....NAVC clinician’s brief ...... consultant on call