Disease of the Voice Box or Larynx in Cats
The voice box, or larynx, serves as a passage for airflow from the external environment to the lungs. It protects the lungs from aspiration during swallowing and regurgitation, and allows for vocalization (such as meowing). Laryngeal disease refers to any condition that alters normal structure and/or function of the voice box or larynx.
In cats, the incidence of laryngeal disease is based on limited reports in the literature, but it appears to be significantly lower than in dogs. Affected cats are usually older, but it is seen occasionally in younger cats secondary to trauma or surgical procedures; the average age in one report was 11 years of age. Cancer of the larynx or voice box generally occurs in middle-aged to older cats. There is no defined breed susceptibility.
Symptoms and Types
Symptoms are directly related to the degree of impairment or restriction of airflow through the voice box or larynx, though acquired paralysis is often associated with exertion, stress, or extreme heat. Some common signs of laryngeal disease include:
- Noisy respiration and a high-pitched sound when breathing in (most common)
- Change in character of the bark
- Occasional coughing
- Reduced activity, exercise intolerance
- Elevated rectal temperature (especially during warm weather months)
Laryngeal disease may be congenital (present at birth) or acquired, most often due an unknown cause. The following are some of the more common causes of laryngeal diseases:
- Vagal nerve abnormality - the vagus nerve supplies nerve fibers to the voice box (larynx), throat (pharynx), windpipe (trachea) and other organs
- Abnormality involving the recurrent laryngeal nerves (branches of the vagus nerve)
- Diseases in the chest - such as infections, inflammation, cancer
- Nervous-system disorders involving multiple nerves
- Abnormalities of muscles (myopathy)
- Immune-mediated disorders
- Possible hormonal deficiencies - such as inadequate production of thyroid hormone (hypothyroidism), or inadequate production of steroids by the adrenal gland (hypoadrenocorticism)
- Penetrating wounds (such as bite wounds) or blunt trauma to the neck
- Injury secondary to ingested foreign materials – such as bones, sticks, needles, pins
- Primary cancer of the voice box (larynx) or spread of cancer into the tissues of the voice box (metastatic cancer)
- Lymphoma (predominant cancer in cats)
- Squamous cell carcinoma and adenocarcinoma (a cancer that originates in glandular tissue)
- Thyroid cancer - may put pressure on or actually invade the recurrent laryngeal nerves
Risk factors include existing lung abnormalities, such as pneumonia and chronic airway disease. Fluid build-up in the space between the chest wall and the lungs (pleural effusion) can also have a significant impact on breathing and may increase the breathing difficulties associated with diseases of the voice box or larynx.
You will need to give a thorough history of your cat's health, onset of symptoms, and possible incidents that might have preceded this condition. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis. One of the possible underlying causes your doctor will be looking for is thyroid disease, particularly if your cat is older.
Some of the diagnostic imaging techniques that may be used to find the underlying disorder are X-ray, fluoroscopy, and bronchoscopy to help rule out other differential diagnoses and to detect aspiration pneumonia. These are all fairly non-invasive techniques, as they do not require surgery to inspect the internal structure of the airways. Ultrasound is also a useful diagnostic tool in the non-invasive diagnosis of laryngeal masses.
To get an even closer look at the larynx, your doctor may conduct a laryngoscopy. Your cat will need to be placed under heavy sedation or anesthesia in order for your veterinarian to evaluate laryngeal abduction on inspiration and to detect whether mass lesions are present.
Laryngeal collapse is a complication of long-standing brachycephalic airway syndrome. Chronic proliferative, pyogranulomatous (granular and pussy) laryngitis will require culture and microscopic examination to define; broad spectrum antibiotics, given beforehand, along with tapered administration of corticosteroids, may be required to obtain an optimal response. Conditions that cause obstruction, such as tracheal collapse or masses close to the larynx, may mimic laryngeal disease. If a mass lesion is found during examination, it may require surgical removal.
Diagnosis of paralysis can be confirmed by a loss of abduction (a change in the position) of the laryngeal cartilages during deep inspiration. Paralysis on only one side may be noted in earlier or milder forms of laryngeal dysfunction.