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Basics ⬇

Basics

Definition

  • Chronic bronchitis-inflammation in the airways (bronchi and bronchioles) lacking a specific etiology; chronic daily cough of greater than 2 months in duration.
  • Asthma-acute or chronic airway inflammation associated with increased airway responsiveness to various stimuli, airway narrowing due to smooth muscle hypertrophy or constriction, reversibility of airway constriction, and presence of eosinophils, lymphocytes, and mast cells within the airways.
  • Bronchitis is thought to result in airflow obstruction due to airway remodeling while asthma is associated with airway constriction; however, clinically the two disease processes can appear similar. No physical examination findings or biomarkers can distinguish between the two syndromes, although reversal of airflow obstruction following administration of a beta-agonist is suggestive of the asthmatic form of disease.

Pathophysiology

  • Lower airway inflammation likely results from inhalation of irritant substances.
  • Bronchiolar smooth muscle constriction-reversible spontaneously or with treatment.
  • Increase in mucosal goblet cells, mucus production, and edema of bronchial wall associated with inflammation.
  • Excessive mucus can cause bronchiolar obstruction, atelectasis, or bronchiectasis.
  • Smooth muscle hypertrophy implies chronicity-usually not reversible.
  • Chronic inflammation leads to airway remodeling and irreversible airflow obstruction.

Systems Affected

  • Respiratory
  • Cardiac-pulmonary hypertension rarely

Geographic Distribution

Worldwide.

Signalment

Species

Cat

Breed Predilections

Siamese overrepresented

Mean Age and Range

Any age; more common between 2 and 8 years

Predominant Sex

One study showed females overrepresented

Signs

Historical Findings

  • Coughing, tachypnea, labored breathing or wheezing.
  • Signs are typically episodic and can be acute or chronic.

Physical Examination Findings

  • Severely affected cats present with open-mouth breathing, tachypnea, and cyanosis.
  • Increased tracheal sensitivity is common.
  • Chest auscultation may reveal crackles and/or expiratory wheezes, but can be normal.
  • Labored breathing with an abdominal push on expiration, increase in expiratory effort.

Causes

Triggers of airway inflammation unknown

Risk Factors

  • Cigarette smoke, poor environmental hygiene, dusty cat litter, hair sprays, and air fresheners can exacerbate disease.
  • Use of potassium bromide-implicated in causing signs of bronchitis/asthma in some cats.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Rule out infectious pneumonia (Mycoplasma, Toxoplasma, bacterial or fungal pneumonia).
  • Consider Dirofilaria immitis and primary lung parasites (Aelurostrongylus abstrusus, Capillaria aerophilia, Paragonimus kellicotti). More common in southern and midwest US, and in outdoor and hunting cats in some geographic regions.
  • Primary or metastatic neoplasia can have similar clinical and radiographic appearance.
  • Clinical presentation of idiopathic pulmonary fibrosis may appear similar to feline bronchitis.

CBC/Biochemistry/Urinalysis

Frequently normal, ∼40% of cats with bronchial disease have peripheral eosinophilia.

Other Laboratory Tests

  • Fecal exams-flotation for Capillaria, sedimentation for Paragonimus, Baermann for Aelurostrongylus. False-negative tests common.
  • Heartworm antigen and antibody testing, particularly if coughing occurs in conjunction with vomiting.
  • Radioallergosorbent testing or intradermal skin testing-no correlation between skin allergies and respiratory disease currently documented.

Imaging

Radiography

  • Classically, diffuse bronchial wall thickening; interstitial or patchy alveolar patterns also possible.
  • Severity of radiographic changes does not necessarily correlate with clinical severity or duration, and normal radiographs can be found.
  • Hyperinflation of lung fields-flattened and caudally displaced diaphragm, increased distance between the heart and diaphragm, extension of lungs to the first lumbar vertebrae thought to reflect bronchoconstriction.
  • Collapse of right middle lung lobe due to mucus plugging and atelectasis reported in 11% of cases.
  • Pulmonary lobar arterial enlargement is suspicious for heartworm disease.

Echocardiography

Useful to document heartworm disease or secondary pulmonary hypertension.

Diagnostic Procedures

Transoral Tracheal Wash

Use a sterile endotracheal tube and polypropylene catheter to collect airway fluids at the level of the carina.

Bronchoscopy

  • Allows visualization of trachea and bronchi. Excessive amounts of thick mucus are common with bronchitis. Mucosa of the airways is typically hyperemic and edematous.

Cytology of TOTW or BAL

  • Eosinophils and neutrophils are most prominent cell types.
  • Up to 20% eosinophils on BAL cytology can be found in normal cats.
  • A mixed inflammatory cell population occurs in about 21% of cats.

Bacterial Cultures

  • Quantitated cultures recommended; positive cultures frequently encountered but bacterial colony counts >100–300 cfu/mL uncommon with bronchitis.
  • Specific Mycoplasma culture often needed.

Biopsy

Keyhole biopsy-can differentiate between idiopathic pulmonary fibrosis, neoplasia and bronchitis if needed.

Pathologic Findings

Hyperplasia/hypertrophy of goblet cells, hypertrophy of airway smooth muscle, epithelial erosion, and inflammatory infiltrates.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Remove patient from environment that exacerbates disease.
  • Hospitalize for acute respiratory distress.

Nursing Care

Oxygen therapy, bronchodilators, and sedatives in an acute crisis. Minimize manipulation in order to lessen stress and oxygen needs of the animal.

Activity

Usually self-limited by patient.

Diet

Calorie restriction for obese cats.

Client Education

  • Most causes are chronic and progressive.
  • Do not discontinue medical therapy when clinical signs have resolved-subclinical inflammation is common and can lead to progression of disease. Lifelong medication and environmental changes usually necessary.
  • Some clients can be taught to give terbutaline subcutaneously and corticosteroid injections at home for a crisis situation.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

Emergency Treatment

  • Oxygen and a parenteral bronchodilator. Injectable terbutaline (0.01 mg/kg IV or SC); repeat if no clinical improvement (decrease in respiratory rate or effort) in 20–30 minutes.
  • A sedative can aid in decreasing anxiety (butorphanol tartrate at 0.2–0.4 mg/kg IV or IM, buprenorphine at 0.01 mg/kg IV or IM, or acepromazine at 0.01–0.05 mg/kg SC).
  • A short-acting parenteral corticosteroid may also be required. Dexamethasone sodium phosphate (0.1–0.25 mg/kg, IV or SC). Can repeat if no improvement noted within 20–30 minutes.

Long-Term Management

Corticosteroids

  • Decrease inflammation.
  • Oral treatment is preferred over injectable for closer monitoring of dose and duration.
  • Prednisolone: 0.5–1 mg/kg PO q12h. Begin to taper dose (50% each week) after 1–2 weeks if clinical signs have improved. Maintenance therapy = 0.5–1 mg/kg PO q24–48h.
  • Longer-acting parenteral steroids (Vetalog or Depomedrol) should be reserved only for situations where owners are unable to administer oral or inhaled medication on a routine basis.

Inhaled Corticosteroids

  • Requires a form-fitting facemask, spacer, and metered-dose inhaler (MDI). Veterinary brand: Aerokat (Trudell Medical).
  • The most common corticosteroid used as an MDI is fluticasone propionate (Flovent). 110-µg Flovent MDI is recommended (1–2 actuations, 7–10 breaths q12h). In one study, use of 44-µg Flovent decreased BAL eosinophil counts in cats with experimentally induced lower airway disease.
  • Flovent is used for long-term control of airway inflammation. Takes 10–14 days to reach peak effect; use oral steroids concurrently during this time.
  • Results in some suppression of the hypothalamic-pituitary axis but systemic side effects appear to be limited.

Bronchodilators

  • Methylxanthines: sustained-release theophylline formulations recommended, and pharmacokinetics can vary greatly. Only generic currently available. Dose at 15–20 mg/kg PO once daily in the evening.
  • Beta-2 agonists (terbutaline, albuterol)-reverse smooth muscle constriction. Oral terbutaline dose is 1/4 of a 2.5 mg tablet q12h. Initial albuterol dose is 20 µg/kg PO q12h; can increase to 50 µg/kg PO q8h.

Inhaled Bronchodilators

  • Albuterol-preferred inhalant bronchodilator, effect lasts less than 4 hours. Long-term use of traditional racemic form of inhaled albuterol (R and S-enantiomers) has been associated with worsened airway inflammation. Enantiomer specific R-albuterol should be used if the drug is needed in moderately to severely affected cats (q12–24h) or during respiratory distress.

Anthelminthics

  • Empirical therapy is indicated for cats with clinical signs of bronchial disease and eosinophilic airway cytology in an appropriate geographic location.
  • Consider fenbendazole, ivermectin, or praziquantel.

Antibiotics

Use based on a positive quantitative culture and susceptibility testing or Mycoplasma isolation.

Contraindications

Beta-2 antagonists (e.g., propranolol) are contraindicated because of their ability to block sympathetically mediated bronchodilation.

Precautions

  • Long-term use of steroids increases risk of development of diabetes mellitus and predisposes to immunosuppression.
  • Use of corticosteroids in cats may precipitate congestive heart failure.
  • Beta agonists could cause tachycardia and exacerbate underlying cardiac disease.

Alternative Drug(s)

Leukotriene receptor blockers and inhibitors of generation: no evidence to support use. Anti-serotonin and antihistamine drugs: no evidence to support use. Immunotherapy: no clinical evidence to support use at this time.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Owners should report any increase in coughing, sneezing, wheezing, or respiratory distress. Medications should be increased appropriately or additional therapy initiated if clinical signs worsen.
  • Follow-up radiographs may be helpful to detect onset of new disease.
  • Owner should watch for signs of PU/PD that could indicate diabetes mellitus or renal disease. Monitor blood glucose and urine cultures.

Prevention/Avoidance

Eliminate any environmental factors that can trigger a crisis situation (see “Risk Factors”). Change furnace and air-conditioner filters on a regular basis. Consider dust-free litters.

Possible Complications

  • Acute episodes can be life-threatening.
  • Right-sided heart disease rarely develops as a result of long-term bronchitis.

Expected Course and Prognosis

  • Long-term therapy should be expected.
  • Most cats do well if recurrence of clinical signs is carefully monitored and medical therapy appropriately adjusted.
  • A few cats will be refractory to treatment; these carry a much worse prognosis.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

Cor pulmonale can be a sequela to chronic lower airway disease.

Pregnancy/Fertility/Breeding

Glucocorticoids are contraindicated in the pregnant animal. Bronchodilators should be used with caution.

Synonyms

Allergic bronchitis, asthmatic bronchitis, feline lower airway disease, extrinsic asthma, eosinophilic bronchitis.

See Also

Abbreviations

  • BAL = bronchoscopy/bronchoalveolar lavage
  • MDI = metered-dose inhaler
  • PU/PD = polyuria/polydipsia

Internet Resources

Suggested Reading

Cohn LA, DeClue AE, Cohen RL, Reinero CR. Effects of fluticasone propionate dosage in an experimental model of feline asthma. J Feline Med Surg 2010, 12(2):91–96.

Kirschvink J, Leemans J, Delvaux F, et al. Inhaled fluticasone reduces bronchial responsiveness and airway inflammation in cats with mild chronic bronchitis. J Feline Med Surg 2006, 8(1):45–54.

Authors Carrie J. Miller and Lynelle R. Johnson

Consulting Editor Lynelle R. Johnson

Client Education Handout Available Online