Merck Manual

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Professional Version

Tonsillitis in Dogs and Cats


Caroline C. Tonozzi

, DVM, DACVECC, Mission Veterinary Partners

Reviewed/Revised Feb 2022 | Modified Oct 2022

Etiology of Tonsillitis in Dogs and Cats

Tonsillitis is uncommon in dogs and in cats. In dogs, it seldom occurs as a primary disease, but when present it is most frequently seen in small breeds. It usually is secondary to nasal, oral, or pharyngeal disorders (eg, cleft palate Congenital Oronasal Fistulas (Cleft Palate and Cleft Lip) Congenital oronasal fistulas result when the palatine shelves fail to fuse during gestation. This fusion typically occurs at 25–28 days of gestation in dogs and 47 days of gestation in horses... read more Congenital Oronasal Fistulas (Cleft Palate and Cleft Lip) ); chronic vomiting or regurgitation (eg, from megaesophagus Dilatation of the Esophagus in Small Animals Megaesophagus may be due to a congenital defect or may be an adult-onset, acquired disorder. Congenital defects that may result in megaesophagus include: vascular ring anomalies esophageal diverticula... read more Dilatation of the Esophagus in Small Animals ); or chronic coughing (eg, with bronchitis Kennel Cough Kennel cough results from inflammation of the trachea. It is a mild, self-limiting disease but may progress to bronchopneumonia in puppies or to chronic bronchitis in debilitated adult or aged... read more ). Chronic tonsillitis may be seen in brachycephalic dogs in association with pharyngitis accompanying soft palate elongation and redundant pharyngeal mucosa. Chronic tonsillitis in young dogs is thought to represent maturation of pharyngeal defense mechanisms.

Escherichia coli, Staphylococcus aureus, and hemolytic streptococci are the pathogenic bacteria most often cultured from diseased tonsils. Plant fibers or other foreign bodies that lodge in the tonsillar fossa may produce a localized unilateral inflammation or a peritonsillar abscess. Other physical and chemical agents may cause irritation of the oropharynx and one or both tonsils. Tonsillitis may also accompany neoplastic tonsillar masses because of physical trauma or secondary bacterial infection.

Clinical Findings and Diagnosis of Tonsillitis in Dogs and Cats

  • Clinical findings

  • Exclusion of other diagnoses or underlying conditions

Tonsillitis is not always accompanied by obvious clinical signs. Fever and malaise are uncommon unless consequent to systemic infection. Gagging, followed by retching or a short, soft cough, may result in expulsion of small amounts of mucus. Inappetence, listlessness, salivation, and dysphagia are seen in severe tonsillitis.

Tonsillar enlargement may range from protrusion just out of the crypts to a mass of sufficient size to cause dysphagia or inspiratory stridor. A septic, suppurative exudate may surround the tonsil, which may be reddened with small necrotic foci or plaques. Tonsillitis usually is a sign of generalized or regional inflammatory disease; therefore, primary tonsillitis should be diagnosed only after underlying diseases have been excluded. Squamous cell carcinoma, malignant melanoma, and lymphosarcoma are common in canine tonsils and should be distinguished from tonsillitis. Tonsillar lymphosarcoma generally results in bilateral symmetric enlargement, whereas nonlymphoid neoplasia is usually unilateral.

Treatment of Tonsillitis in Dogs and Cats

  • Antibiotics

  • Supportive care

Prompt systemic administration of antibiotics is indicated for bacterial tonsillitis. Penicillins are often effective, but in refractory cases, culture and sensitivity testing may be needed. Mild analgesics are appropriate for severe pharyngeal irritation, and a soft, palatable diet is recommended for a few days until the dysphagia resolves. Parenteral administration of fluids is required for those animals unable to take food by mouth.

Tonsillectomy is rarely required for chronic primary tonsillitis but provides permanent relief. Other indications for tonsillectomy include tonsillar neoplasia and tonsillar enlargement that interferes with airflow (eg, in brachycephalic breeds).

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