Within the realm of feline health, one enigmatic condition that demands our attention is asthma—a recurring respiratory disturbance characterized by the constriction (narrowing) of the airways in the lungs. This complex ailment encompasses three defining features:
- Airway inflammation
- Airway hyper-responsiveness
- Reduced airflow (partially reversible)
In simpler terms, this condition leads to inflamed airways that are unusually reactive to mental stress or respiratory irritants, leading to reduced air movement in the lungs. When all three features converge, we can confidently diagnose asthma.
Peering into the Lungs: Unveiling Asthma's Core
A cascade of events occurs within the lungs of cats grappling with asthma. Excessive mucus accumulates in the airways. Subsequently, inflammation causes the airway walls to swell and, in some cases, ulcerate. Lastly, the airway muscles go into spasms, culminating in constriction. This constricted state makes deep breathing difficult, induces exercise intolerance, triggers coughing, and results in distinct musical sighs known as "wheezes." However, not all these symptoms may manifest concurrently. While some cats may exhibit a persistent, low-grade cough, it's crucial to acknowledge that asthmatic crises can arise suddenly, potentially posing life-threatening situations. Asthmatic airway constriction can occur spontaneously, in response to stress or anxiety, or even as an allergic reaction.
Bridging the Gap: Human vs. Feline Asthma
The term "asthma" was bestowed upon the feline ailment due to its resemblances to human asthma. As of now, it appears that all the diagnostic criteria applicable to humans are relevant to cats as well. However, we're still untangling the intricacies of this syndrome in feline patients. While we know that humans experience actual asthma symptoms episodically despite continuous airway disease, it remains uncertain whether feline airways are consistently diseased or if structural changes only occur during visible distress.
Deciphering the Diagnosis
Due to the constricted airways, the volume of air a cat can draw in and expel with each breath diminishes. Often, labored breathing is observable, with the visible effort exerted in expelling air. The abdomen may contract to aid air expulsion, and breaths become shallow and rapid. Cats may resort to breathing with an open mouth to maximize air intake.
Proceeding with the diagnosis of feline asthma typically entails a chest radiograph, provided the cat's distress doesn't impede the procedure. This radiograph frequently reveals "air-trapping," indicating that the small airways have contracted, preventing exhalation. The lungs might appear larger than normal due to over-inflation, and the diaphragm could appear flattened as a result.
Radiographs can provide detailed views of the tiny airways. These airways stand out due to the mucus and inflammatory fluid within them, resembling "doughnuts" (when viewed head-on) or "tramlines" (when seen from the side). These findings are classical markers of airway disease.
A Diagnostic Conundrum
Not all asthmatic cats exhibit visible radiographic changes, leading to potential overdiagnosis. Diagnosing asthma can be intricate, and it's notably underdiagnosed, with up to 23% of affected cats having completely normal radiographs.
The presence of a coughing cat with unremarkable chest radiographs creates a diagnostic puzzle. Even with evident radiographic changes, distinguishing among various conditions can be challenging. Additionally, feline heart disease, where the heart muscle thickens without altering the external heart shape, might resemble asthma. In heartworm-endemic regions, feline heartworm disease must also be considered. For cases where anesthetic risk isn't excessively high, a tracheal wash and/or bronchoscopy could be contemplated, though these often yield inconclusive results. CT scans hold promise as a diagnostic tool, but their availability remains limited.
Unveiling Clarity through Therapeutic Response
A pivotal attribute of asthma is its reversible airway constriction. During emergencies, a small dose of epinephrine or terbutaline can swiftly reverse an asthmatic crisis in just 15 minutes. Response to an injectable corticosteroid like dexamethasone typically yields positive results within 30 minutes.
Sometimes, diagnostic tests leave questions unanswered, and treatment response becomes the corroborative evidence. Effective asthma treatment, often with oral prednisone initially, followed by transitioning to a metered dose inhaler, bolsters the diagnosis. This switch minimizes potential corticosteroid side effects.
Crafting a Treatment Tapestry
The cornerstone of asthma treatment revolves around countering inflammation, the root cause of constriction. Corticosteroid medications form the bedrock of therapy, available in pill, injectable, or inhaler forms. Oral corticosteroids like prednisolone or long-acting injections like Depo-Medrol are typically the starting points. Their affordability and effectiveness help verify the diagnosis. Inhaler use, such as Flovent®, is increasingly favored, as its localized delivery reduces systemic side effects.
Metered dose inhalers, previously used exclusively by humans, now benefit cats thanks to pediatric spacer devices. These devices solve the inhalation predicament by delivering medication to the airways, sparing the rest of the body from undue exposure. Cats inhale from a mask attached to the spacer, taking approximately 7 to 10 breaths. Corticosteroid inhalers are employed for long-term management, while airway dilator inhalers like Proventil® or Ventolin® alleviate flare-ups.
Initially, a combination of oral prednisone and a metered dose inhaler is administered, with a gradual transition to the inhaler alone.
Exploring Alternatives in Treatment
Other potentially beneficial medications encompass:
- Allergen-Specific Immunotherapy: Beneficial for many cats, this "allergy shot" approach aids asthmatics by gradually desensitizing them to allergens. While not a quick fix, it offers long-term benefits. Veterinary dermatologists typically oversee this therapy.
- Airway Dilators: Terbutaline (Brethine®) and theophylline, used in asthma management, alleviate constriction. Terbutaline can be administered orally or via injection. Keeping injectable terbutaline at home for crises can be advised. Theophylline, an oral medication, is taken once daily before bedtime.
- Cyclosporine: A newcomer to asthma treatment, cyclosporine, an immunomodulator used in organ transplant patients, is used when other treatments prove inadequate. Blood level monitoring increases treatment costs.
Mindful of the Air
Mitigating air irritants benefits asthmatic cats:
- Ban cigarette smoke from the environment.
- Opt for dustless cat litter.
- Choose non-topical insecticides to minimize sprays.
- Regularly replace home air filters.
Crucially, asthma can culminate in a life-threatening respiratory crisis. If a cat exhibits mouth breathing, heightened abdominal movement during breathing, and isn't purring, immediate veterinary attention is vital.
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