The Core Distinction: Asthma vs. Chronic Bronchitis
Feline lower airway disease almost always boils down to two diagnoses: asthma and chronic bronchitis. They look similar clinically and radiographically, but the underlying pathology is different — and the NAVLE tests whether you know which is which.
Feline asthma is a reversible, type I hypersensitivity-mediated bronchoconstriction. An allergen triggers mast cell degranulation → bronchospasm, mucus hypersecretion, and airway edema → air trapping → hyperinflation. The airways can normalize between episodes. Siamese and other Oriental breeds are disproportionately affected. Young to middle-aged cats are the classic demographic, though any cat can develop it.
Chronic bronchitis is irreversible airway remodeling from persistent inflammation. It tends to affect older cats. The inflammation is predominantly neutrophilic rather than eosinophilic. Cats with chronic bronchitis may not respond as well to corticosteroids as asthmatic cats do. The two conditions overlap — a cat can have both — and distinguishing them requires BAL cytology.
Pathophysiology in One Pass
The sequence matters for understanding both the clinical signs and the treatment targets. Allergen exposure activates IgE-sensitized mast cells in the airway mucosa. Histamine, leukotrienes, and prostaglandins are released, driving three simultaneous effects: smooth muscle contraction (bronchospasm), increased mucus secretion from goblet cells, and mucosal edema. The net result is narrowed, partially obstructed airways that trap air on expiration. Air trapping causes pulmonary hyperinflation — the barrel-chested appearance and flattened diaphragm you see on radiographs.
In the acute episode, the cat cannot exhale effectively. The expiratory phase is prolonged and effortful, which produces the audible wheeze and the classic crouched posture with neck extended. The cat is trying to reduce airway resistance by straightening the trachea. Open-mouth breathing indicates severe hypoxemia.
Clinical Presentation
Acute asthmatic episode: open-mouth breathing, expiratory wheeze, crouched posture with neck extended and elbows abducted. Cyanotic mucous membranes signal severe disease. These episodes can progress to respiratory arrest if not treated.
Chronic or mild disease: recurrent cough (often mistaken by owners for hairballs), mildly increased respiratory rate, intermittent wheeze. Some cats are only mildly symptomatic for months before owners present them.
Chronic bronchitis looks similar — persistent cough, exercise intolerance — but the acute bronchospasm episodes are less prominent than in asthma.
Radiographic Findings
The classic radiographic pattern in feline asthma is bronchial. Two patterns tell you you are looking at thickened airway walls:
- Donut sign — airways seen end-on appear as thick-walled circles
- Tram tracks (tramlines) — airways seen longitudinally appear as parallel dense lines
Supporting findings: pulmonary hyperinflation, flattened diaphragm on lateral view, and — in classic asthma — right middle lung lobe collapse presenting as a triangular opacity adjacent to the cardiac silhouette.
Diagnosis
Clinical signs plus compatible radiographs establish a working diagnosis. To confirm and classify, you need bronchoalveolar lavage (BAL). Cytology is the key result:
- Asthma: >17% eosinophils (some sources use >5% as threshold for abnormal)
- Chronic bronchitis: predominantly neutrophilic (>14%), non-septic
- Bacterial pneumonia: septic neutrophilic (intracellular bacteria)
Before doing BAL, rule out Aelurostrongylus abstrusus (feline lungworm). It produces eosinophilic airway inflammation that is cytologically indistinguishable from asthma. Run a fecal Baermann test — standard flotation misses the first-stage larvae. In heartworm-endemic areas, run both a heartworm antigen and antibody test. Heartworm-associated respiratory disease (HARD) in cats mimics asthma clinically and radiographically and does not respond to bronchodilators.
Asthma vs. Heartworm vs. Lungworm
Treatment: Acute Crisis
The acutely dyspneic cat needs three things: oxygen, bronchodilation, and minimal stress. Move fast and handle gently.
Flow-by or cage
0.01 mg/kg SC/IM
or albuterol MDI if stable
0.5–1 mg/kg IV/IM
if severely distressed
Injectable terbutaline is preferred over inhaled albuterol in the acute crisis because a cat in severe distress cannot take the deep, slow breaths needed to get inhaled medication into the lower airways. Subcutaneous injection delivers reliable bronchodilation quickly with minimal restraint.
Albuterol MDI via AeroKat chamber (90 mcg/puff, 2 puffs) is appropriate for moderate episodes where the cat is distressed but not cyanotic, or as a rescue inhaler sent home with owners of well-managed asthmatic cats.
Treatment: Chronic Management
The goal of long-term management is suppressing airway inflammation and preventing airway remodeling. Steroids are the cornerstone, but the route matters enormously in cats.
Inhaled fluticasone (220 mcg/puff via AeroKat chamber, q12h) is preferred over systemic steroids for chronic management. Inhaled delivery targets the airways directly, reduces systemic absorption, and avoids the major side effects of long-term oral steroids in cats: iatrogenic diabetes mellitus and immunosuppression. Studies show roughly 80% of steroid-dependent asthmatic cats can be controlled on inhaled therapy alone.
Systemic prednisolone is still appropriate when owners cannot use the inhaler consistently, or during periods of active inflammation that need faster systemic control. Dose down to the lowest effective amount as soon as possible.
Environmental modification reduces allergen load and trigger frequency: eliminate aerosol sprays, switch to low-dust litter, remove cigarette smoke and scented candles from the home. These changes alone can significantly reduce episode frequency in sensitized cats.
Asthma vs. Chronic Bronchitis: Side-by-Side
Feline Asthma
- Reversible bronchospasm
- Type I hypersensitivity (IgE-mediated)
- Young–middle-aged; Siamese overrepresented
- BAL: eosinophilic (>17% eos)
- Responds well to corticosteroids
- Acute crisis episodes typical
Chronic Bronchitis
- Irreversible airway remodeling
- Chronic irritant/inflammatory
- Older cats; any breed
- BAL: neutrophilic (>14% neutrophils, non-septic)
- Partial or poor steroid response
- Chronic persistent cough predominates
Prognosis
Cats with well-controlled asthma live normal lifespans. The concern is inadequate long-term management: chronic, uncontrolled inflammation leads to irreversible airway remodeling, smooth muscle hypertrophy, and eventually emphysema. Recurrent severe episodes carry risk of spontaneous pneumothorax from rupture of hyperinflated alveoli. Cats with chronic bronchitis have a variable prognosis depending on severity of remodeling at diagnosis — the irreversibility means early intervention matters more than in asthma.