Disease of the Voice Box or Larynx in Dogs
The voice box, or larynx, protects the lungs from aspiration during swallowing and regurgitation, allows for vocalization (such as barking and growling), and serves as a passage for airflow from the external environment to the lungs. Laryngeal disease refers to any condition that alters normal structure and/or function of the voice box or larynx.
Paralysis of the larynx is an inherited disorder in the Bouvier des Flandres breed (inherited as an autosomal dominant trait); genetic susceptibility is also suspected, but unproven, in Siberian huskies and bull terriers. Paralysis of the voice box or larynx as part of a condition involving multiple nerves throughout the body (laryngeal paralysis, or polyneuropathy complex) in young Dalmatians and rottweilers, and is considered to be inherited, but a genetic basis is presently unproven.
Symptoms and Types
Hereditary paralysis of the voice box or larynx in dogs is part of a generalized disorder involving several nerves (polyneuropathy syndrome). Symptoms of hereditary paralysis can vary from breed to breed. In Bouvier des Flandres, onset may show around four to six months of age; in Dalmatians, around four to eight months; in rottweilers, around eleven to thirteen weeks of age; and in white-coated German shepherd dogs, around four to six months of age. In addition, medical literature suggests a reported incidence of males being affected at a rate of up to three times more often than females.
Acquired paralysis (a condition that develops sometime later in life/after birth) of the voice box or larynx in dogs has been seen in higher numbers in giant-breed dogs such as St. Bernards and Newfoundlands, and in large-breed dogs such as Irish setters, Labrador retrievers, and golden retrievers. In the acquired form, the reported incidence shows males being affected twice as often as females.
Symptoms of both of these types 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 voice box or larynx paralysis 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)
- Squamous cell carcinoma – a form of cancer of the carcinoma type that may occur in many different organs, including the skin, lips, mouth, esophagus, urinary bladder, prostate, lungs, vagina, and cervix
- Rhabdomyosarcoma – a fast-growing, highly malignant tumor
- Undifferentiated carcinoma
- Oncocytoma – a salivary gland tumor made up of oncocytes, a large granular acidophilic cell
- Lipoma – a benign tumor composed of fatty tissue
- Thyroid carcinoma - may put pressure on or actually invade the recurrent laryngeal nerves
- Mast-cell tumor – mast cells play an important protective role, being intimately involved in wound healing and defense against pathogens, but they can also form tumors
- Osteosarcoma – a malignant bone cancer
- Fibrosarcoma – a malignant tumor derived from fibrous connective tissue
- Melanoma – a malignant tumor of the melanocytes, the melanin producing cells of the skin, eyes and bowel
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 dog'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 dog 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 dog 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.