Tonsillitis is common in dogs but rare 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); chronic vomiting or regurgitation (eg, from megaesophagus); or chronic coughing (eg, with bronchitis). 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.
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.
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).