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Basics ⬇

Basics

Definition

  • The larynx is made of cartilage structures surrounding the rima glottis. The functions of the larynx are to control airflow during respiration, protect the lower airways from aspiration during swallowing, and control phonation.
  • Laryngeal diseases in dogs and cats include laryngeal paralysis, acute laryngitis, obstructive laryngitis, laryngeal collapse in brachycephalic airway syndrome (BAS), foreign body obstruction, neoplasia, and trauma.

Pathophysiology

  • Decreased diameter of the laryngeal opening increases resistance to airflow and results in stridor on inspiration. The decrease in airflow will lead to hypoxemia, cyanosis, or respiratory distress and a decrease in heat exchange (heat intolerance, hyperthermia).
  • Inflammation or lesions of the vocal cords can lead to aphonia or change in bark/meow.

Systems Affected

  • Respiratory-aspiration pneumonia and hypoventilation with cyanosis can occur when laryngeal function is impaired.
  • Cardiovascular-hypoxemia may lead to tachycardia.
  • Gastrointestinal-retching, regurgitation, vomiting, and/or dysphagia can when polyneuropathy causes laryngeal paralysis and esophageal dysfunction; esophagitis is frequently associated with BAS.
  • Nervous-depression, stupor, or coma may occur if severe laryngeal obstruction leads to severe hyperthermia.

Genetics

  • Juvenile laryngeal paralysis in the Bouvier des Flandres is transmitted as a dominant trait.
  • In laryngeal paralysis associated with polyneuropathy in the Leonberger dog, X-linked inheritance is suggested.
  • No other laryngeal disorder has been proven to be genetic in the dog or cat, but familial conditions and breed predispositions have been reported.

Incidence/Prevalence

  • More common in dogs than in cats.
  • Currently, congenital laryngeal paralysis is only sporadic in the Bouvier des Flandres.
  • Idiopathic laryngeal paralysis is a common disease of older large-breed dogs; exact prevalence unknown.
  • BAS is a common syndrome in French and English bulldogs.
  • Laryngeal trauma and neoplasia are rare.

Signalment

Species

Dog and cat

Breed Predilections

  • Familial laryngeal paralysis/polyneuropathy complex occurs in the Dalmatian, rottweiler, Leonberger, and Pyrenean mountain dog (Great Pyrenees).
  • Congenital laryngeal paralysis is found in Bouvier des Flandres, huskies, husky-crosses, white German shepherds, and probably bull terriers.
  • Idiopathic acquired laryngeal paralysis is most often found in large-breed dogs (especially Labrador and golden retrievers).
  • BAS is found in brachycephalic breeds of dogs.
  • Golden retrievers are prone to laryngeal rhabdomyoma.
  • Upper airway obstruction due to laryngeal collapse or narrowed laryngeal opening occurs in Norwich terriers.

Mean Age and Range

  • Congenital and familial laryngeal paralysis-onset of signs usually in the first months of life (2 and 8 months). Later in the Leonberger, 1–9 years, and white German shepherd, 2 years.
  • Acquired laryngeal paralysis-possible at any age but more frequent in older dogs.
  • Neoplasia-middle-aged to old dogs.

Signs

Historical Findings

  • Panting.
  • Exercise and heat intolerance.
  • Noisy respiration.
  • Change of voice.
  • Occasional cough.
  • Severe cases-inspiratory respiratory distress, collapse, syncope, or even sudden death.
  • Polyneuropathy, polymyopathy, or myasthenia gravis-regurgitation, weakness, abnormal gait (pattern of abnormalities varies).
  • Absence of signs is possible in Norwich terriers with upper airway obstruction.

Physical Examination Findings

  • Panting, polypnea, and inspiratory stridor in canine cases.
  • Respiration is less noisy in cats with laryngeal disease.
  • Cyanosis.
  • Hyperthermia frequent.
  • Aspiration pneumonia-fever, crackles on respiratory auscultation.
  • Polyneuropathy, polymyopathy, or myasthenia gravis-paraparesis or tetraparesis with decreased spinal reflexes.
  • Leonberger with familial polyneuropathy-high-stepping pelvic-limb gait with depressed spinal and cranial nerve reflexes.
  • Rottweilers with laryngeal paralysis/polyneuropathy complex-cataracts frequently observed.
  • Normal physical examination in some Norwich terriers with upper airway obstruction.

Causes

  • Laryngeal paralysis:
    • Congenital-(1) neuronal degeneration of the nucleus ambiguous (Bouvier des Flandres and husky); (2) idiopathic.
    • Acquired-(1) polyneuropathy-idiopathic; familial (laryngeal paralysis-polyneuropathy complex); immune-mediated; (2) myasthenia gravis; (3) polymyopathy-idiopathic; immune-mediated; infectious (toxoplasmosis, neosporosis); (4) ventral cervical or cranial thoracic lesion-neoplasia or trauma affecting one or both recurrent nerves; examples include lymphoma of the vagus nerve in the cat and traumatic neuropathy secondary to thyroidectomy.
  • Acute laryngitis:
    • Cause often not found.
    • Virus-canine parainfluenza virus, feline herpes virus 1.
    • Bacteria-Bordetella bronchiseptica.
    • Gastroesophageal reflux.
  • Idiopathic chronic obstructive laryngitis (lymphoplasmacytic, granulomatous)
  • Laryngeal neoplasia:
    • Dog-rhabdomyoma, rhabdomyosarcoma, adenocarcinoma, squamous cell carcinoma, lipoma, extramedullary plasmacytoma.
    • Cat-lymphoma, squamous cell carcinoma.
  • Trauma: injuries caused by foreign bodies.
  • Neck trauma, bite wounds.
  • Laryngeal collapse secondary to BAS.
  • Idiopathic laryngeal malformation, collapse in Norwich terriers.

Risk Factors

Breed associations. Risk factors for developing severe or fatal clinical signs include obesity, hot or humid temperature (especially in a closed environment), and concurrent lower airway or pulmonary disease.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Pharyngeal diseases – also cause gagging, stridor, and cough. Dysphagia is not seen with laryngeal disease but may be present in the case of pharyngeal lesion.
  • Tracheal diseases may be confused with laryngeal disease in some cases. Cough is more frequent in tracheal disease than in laryngeal disease while inspiratory stridor is more frequent in laryngeal disease.

CBC/Biochemistry/Urinalysis

  • No specific abnormalities.
  • Leukocytosis may be present in aspiration pneumonia.
  • Mild-to-moderate increase in liver enzymes if chronic hypoxemia.
  • Hypercholesterolemia may be present if concurrent hypothyroidism is present.

Other Laboratory Tests

  • If laryngeal paralysis secondary to polyneuropathy/polymyopathy:
    • Thyroid panel in the dog
    • Antibody titers against Toxoplasma gondii (dog and cat) and Neospora caninum (dog)
    • Anticholinesterase receptor antibody titer.

Imaging

  • Thoracic radiographs-to rule-out aspiration pneumonia as a complication, other lower airway conditions, and a mediastinal mass as a cause of laryngeal paralysis.
  • If vomiting/regurgitation present-barium swallow with fluoroscopy (to identify esophageal dysfunction, reflux esophagitis/hiatal hernia coexisting in some cases of brachycephalic airway syndrome).
  • Pharynx/larynx radiographs or ultrasonography-to identify potential mass.

Diagnostic Procedures

Laryngoscopy

  • Method of choice to identify laryngeal paralysis, collapse, mass, trauma, foreign body, or laryngitis.
  • General anesthesia or deep sedation is required.
  • Laryngeal paralysis:
    • Diagnosis confirmed by loss of abduction of arytenoid cartilages during deep inspiration.
    • Usually bilateral but unilateral paralysis is possible in the early course of the disease.
    • Unilateral paralysis has been described in cats.
    • False-positive result possible because of the influence of general anesthesia on laryngeal function. Intravenous doxapram HCl (1–2 mg/kg) to increase respiratory effort is advised if the diagnosis is in doubt.

Esophagoscopy

When vomiting/regurgitation is observed to rule out reflux esophagitis or hiatal hernia.

Retrograde Rhinoscopy

When pharyngeal disease is suspected or in the case of BAS.

Pathologic Findings

  • Laryngeal paralysis:
    • Gross findings-redness, swelling, and thickening of the arytenoid cartilages and the vocal folds.
    • Histopathology-nonspecific edema and inflammation of laryngeal mucosa and submucosa; denervation atrophy of laryngeal muscles in the case of neuropathy of recurrent laryngeal nerve(s).
  • Idiopathic chronic obstructive laryngitis:
    • Histopathology-lymphoplasmacytic, granulomatous, or pyogranulomatous inflammation of the laryngeal submucosa.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

Paralysis:

  • Outpatient medical management-for stable patients awaiting surgery.
  • Emergency:
    • Sedation/anesthesia.
    • Prednisolone succinate (30 mg/kg IV, then 15 mg/kg IV after 6 hours, prednisolone 0.5 mg/kg PO q12h till surgery).
    • Cooling therapy with IV fluids, a blowing fan, and cold water on the neck or alcohol on paws.

Nursing Care

Paralysis:

  • Avoid warm, poorly ventilated environments, stress, and intense excitation as these further compromise normal cooling mechanisms and proper air exchange.
  • Avoid cervical collars.
  • Avoid weight gain.

Activity

Exercise should be severely restricted in animals suffering from laryngeal paralysis, especially in warm temperatures.

Diet

Loss of weight is advocated in overweight patients with laryngeal paralysis.

Client Education

  • Paralysis:
    • Discuss the importance of surgery and the risk of not performing surgery (chronic hypoxemia, heat stroke, risk of suffocation, and death)
    • Discuss potential complications of surgery
    • Discuss the guarded prognosis with surgery in cases with polyneuropathy
    • Discuss the potential heritability of this condition in certain breeds.
  • Neoplasia:
    • Discuss surgical/chemotherapeutical options.

Surgical Considerations

  • Paralysis-surgery (unilateral arytenoid lateralization) is the treatment of choice in both dogs and cats; bilateral surgical correction is not advised because it increases the risk of aspiration pneumonia; oral prednisolone therapy (anti-inflammatory doses) should be given for a few days before surgery to decrease laryngeal edema.
  • Neoplasia-surgery can be curative in some cases, for rhabdomyoma, rhabdomyosarcoma, lipoma or squamous cell carcinoma; tracheostomy may improve quality of life if surgical excision is not possible.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • Paralysis-if surgery is declined, oral prednisolone therapy (0.5 mg/kg q12h for 1 week then progressive tapering of dosage to 0.5 mg/kg q48h).
  • Lymphoma (mainly in cats)-chemotherapy (see Lymphoma-Cats).

Precautions

Usual safety precautions if chemotherapy is administered.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Immediate post-surgical period-check rectal temperature (should remain normal).
  • Monitor for aspiration pneumonia (short and long term).
  • If surgery is successful, exercise, stridor, and heat intolerance should decrease.

Possible Complications

  • Paralysis-recurrence of clinical signs are uncommon if surgery is correctly performed; aspiration pneumonia is possible as the larynx is placed in a fixed open position; risk of aspiration pneumonia increased if bilateral arytenoid lateralization is performed or if dysphagia due to pharyngeal and/or esophageal dysfunction coexists.
  • Tumor-recurrence of clinical signs if complete resection is not possible, increased risk of aspiration pneumonia in the postoperative period.

Expected Course and Prognosis

  • Idiopathic paralysis-good with surgery; guarded to poor if surgery is declined.
  • Paralysis associated with esophageal dysfunction-poor.
  • Tumor-guarded to good in the case of successful resection of a benign tumor; poor in the case of carcinoma, even with radiation therapy; variable in the case of feline lymphoma.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

  • Laryngeal paralysis is sometimes associated with a mass in the anterior mediastinum or the ventral cervical region.
  • Coexistence of megaesophagus, weakness, or abnormal gait with laryngeal paralysis suggests polyneuropathy, polymyopathy, or myasthenia gravis.

Age-Related Factors

Congenital and familial laryngeal paralysis-onset of clinical signs in the first year of life.

Pregnancy/Fertility/Breeding

Dogs affected with congenital laryngeal paralysis or laryngeal paralysis/polyneuropathy complex should not be bred.

Abbreviations

  • BAS = brachycephalic airway syndrome

Suggested Reading

Gabriel A, Poncelet L, Van Ham L, Clercx C, Braund KG, Bhatti S, Detilleux J, Peeters D. Laryngeal paralysis-polyneuropathy complex in young related Pyrenean mountain dogs. J Small Anim Pract 2006, 47:144–149.

Hammel SP, Hottinger HA, Novo RE. Postoperative results of unilateral arytenoid lateralization for treatment of idiopathic laryngeal paralysis in dogs: 39 cases (1996–2002). J Am Vet Med Assoc 2006, 228:1215–1220.

Johnson LR, Mayhew PD, Steffey MA, Hunt GB, Carr AH, McKiernan BC. Upper airway obstruction in Norwich Terriers: 16 cases. J Vet Intern Med 2013, 27(6):1409–1415.

Schachter S, Norris CR. Laryngeal paralysis in cats: 16 cases (1990–1999). J Am Vet Med Assoc 2000, 216;1100–1103.

Authors Dominique Peeters and Cécile Clercx

Consulting Editor Lynelle R. Johnson

Client Education Handout Available Online