Salivary Disorders in Small Animals
Ptyalism is drooling of saliva. This may be caused by hypersialosis (hypersecretion of saliva) or pseudoptyalism (secondary to conformational abnormalities or swallowing disorders in animals producing a normal quantity of saliva). Both are discussed together as ptyalism.
Ptyalism may result from the following: 1) drugs, toxins, or poisons, eg, organophosphates; 2) local irritation or inflammation associated with stomatitis, glossitis (especially in cats), oral foreign bodies, neoplasms, injuries, or other mucosal defects; 3) infectious diseases (eg, rabies), the nervous form of distemper, or other convulsive disorders; 4) motion sickness, fear, nervousness, or excitement; 5) reluctance to swallow or interference with swallowing (from irritation of the esophagus, esophageal obstruction by regional pathology, or from stimulation of GI receptors caused by gastritis or enteritis); 6) sublingual lesions (eg, linear foreign body, tumor); 7) tonsillitis; 8) administration of medicine (particularly in cats); 9) conformational defects (eg, heavy, pendulous lower lips); 10) metabolic disorders (eg, hepatic encephalopathy [especially in cats]) or uremia; 11) abscess or other inflammatory blockage or condition of the salivary gland.
The possibility of rabies should be eliminated before oral examination. The underlying cause, local or systemic, should be determined and treated. Acute moist dermatitis of the lips and face may develop if the skin is not kept as dry as possible. Cleansing with a dilute chlorhexidine solution or benzoyl peroxide may be helpful.
A salivary mucocele (or sialocele) is an accumulation of saliva in the submucosal or subcutaneous tissues after damage to the salivary duct or gland capsule. This is the most common salivary gland disorder of dogs. Although any of the salivary glands may be affected, the ducts of the sublingual and mandibular glands are involved most commonly. Saliva often collects in the intermandibular or cranial cervical area (cervical mucocele). It can also collect in the sublingual tissues on the floor of the mouth (sublingual mucocele or ranula). A less common site is in the pharyngeal wall (pharyngeal mucocele) or lower eyelid (zygomatic mucocele).
The cause may be traumatic or inflammatory blockage or rupture of the duct or capsule (with damage of parenchyma) of the sublingual, mandibular, parotid, or zygomatic salivary gland. Usually, the exact cause is not determined, but a developmental predisposition in dogs has been suggested.
Signs depend on the site of saliva accumulation. In the acute phase of saliva accumulation, the inflammatory response results in the area being swollen and painful. Frequently, this stage is not seen by the owner, and the first noticed sign may be a nonpainful, slowly enlarging, fluctuant mass, frequently in the cervical region. A ranula may not be seen until it is traumatized and bleeds. A pharyngeal mucocele can obstruct the airways and result in moderate to severe respiratory distress. A zygomatic mucocele may result in exophthalmos or enophthalmos, depending on its size and location.
A mucocele is detectable as a soft, fluctuant, painless mass that must be differentiated from abscesses, tumors, and other retention cysts of the neck. Pain or fever may be present if the mucocele becomes infected. A salivary mucocele usually can be diagnosed by palpation and aspiration of light brown or blood-tinged, viscous saliva. Usually, careful palpation with the animal in dorsal recumbency can determine the affected side; if not, sialography may be helpful.
Surgery is recommended to remove the damaged salivary gland and duct. Periodic drainage if surgery is not an option is usually only a temporary measure and has the potential for iatrogenic infection. Marsupialization is often ineffective. Gland-duct removal has been recommended for curative treatment of salivary mucoceles.
Salivary fistula is an uncommon problem that can result from trauma to the mandibular, zygomatic, or sublingual salivary glands. Wounds of the parotid gland are most likely to develop a fistula. Parotid duct injury may be the result of a traumatic wound (eg, bite wound), abscess drainage, or prior surgery in the area with iatrogenic rupture. The constant flow of saliva prevents healing, and a fistula develops.
History of injury in the gland area, location of the fistula, and nature of the discharge are characteristic. A salivary fistula must be differentiated from a draining sinus (due to a penetrating foreign body or endodontic disease of a mandibular tooth) in the neck or from sinuses arising from congenital defects. Surgical ligation of the duct usually results in resolution, but excision of the associated gland may also be necessary.
Salivary gland tumors are rare in dogs and cats, although cats are affected twice as frequently as dogs. Most are seen in dogs and cats >10 yr old. There is no clear breed or sex predilection, although Poodles and Spaniel breeds may be predisposed. Most salivary gland tumors are malignant, with carcinomas and adenocarcinomas the most common. Local infiltration and metastasis to regional lymph nodes and lungs are common, as is local recurrence after surgical excision. Radiotherapy, with or without surgery, offers the best prognosis.
Sialadenitis, or inflammation of the salivary gland, is rarely a clinical problem in dogs and cats. However, it is frequently an incidental finding on histopathology at necropsy.
The cause may be trauma from penetrating wounds or systemic infection affecting the salivary gland or surrounding tissue. Sialadenitis as a component of systemic disease has been reported with rabies, distemper, and the paramyxovirus that causes mumps in people.
Signs include fever, depression, and painful, swollen salivary glands. Rupture of an abscessed gland discharges pus into the surrounding tissue or the mouth. Rupture through the skin may cause a salivary fistula to form. Swelling of the parotid gland is most prominent below the ear, swelling of the mandibular gland at the angle of the jaw, and swelling of the zygomatic gland just caudal to the eye. Zygomatic gland involvement may result in retrobulbar swelling, divergent strabismus of the affected eye, exophthalmos, excess tearing, and reluctance to open the mouth or eat. Abscesses of the zygomatic and parotid glands are acutely painful; the animal may hold its head rigidly and resent any manipulation involving the head or neck.
Radiographs and laboratory tests are usually not helpful, although evaluation of fluid in an abscess can lead to a diagnosis. Histopathology of salivary gland tissue can reveal acute or chronic inflammatory changes or necrosis.
Mild sialadenitis requires no treatment, and recovery is usually rapid and complete. A developed abscess should be drained through the overlying skin or, if involving the zygomatic gland, behind the last upper molar on the affected side. Systemic antibiotics should be administered.
Lack of resolution or recurrence necessitates cytology of aspirated material, biopsy, or surgical removal of the affected gland.
Sialadenosis is a non-inflammatory, non-neoplastic, usually bilateral enlargement of the mandibular salivary glands, associated with regional swelling (dependent on location) and exophthalmos but no apparent pain. The dog may retch and gulp, which is elicited by mild excitement and occurs several times a day. There may be weight loss, reluctance to exercise, snorting, lip smacking, nasal discharge, hypersalivation, inappetence, and depression. Histologically, there are no obvious abnormalities. Excessive saliva production may be associated with increased parasympathetic activity or changes in sympathetic innervation. Phenobarbital administration usually results in lasting improvement, providing support for a neurogenic pathogenesis.
Necrotizing sialometaplasia has also been termed salivary gland necrosis or infarction. There is squamous metaplasia of the salivary gland ducts and lobules, with ischemic necrosis of the salivary gland lobules. It can be seen in dogs (mostly small breeds such as terriers) of all ages, most often 3–8 yr old. Affected dogs usually are depressed, nauseous, and anorectic. Clinical signs include salivary gland enlargement that may be painful on palpation, weight loss, ptyalism, retching, gagging, regurgitation, and vomiting. Other signs include persistent swallowing, lip smacking, coughing, tachypnea, dyspnea, and abdominal respiration. Examination of samples from fine-needle aspirates or biopsies often reveal no abnormalities. Diagnosis requires excluding other causes of enlargement. Surgical removal of the affected salivary gland produces minimal if any improvement. Pain management, antibiotics (based on culture and sensitivity of the fluid/tissue aspirate), NSAIDs, antiinflammatory doses of glucocorticoids, and control of internal parasites have resulted in favorable responses in some cases. Phenobarbital administration (1–2 mg/kg, PO, bid, or higher initial doses) has resulted in dramatic improvement in several cases, providing more support for a neurogenic pathogenesis..
Hypoptyalism is a decreased secretion of saliva that can result in a dry mouth (xerostomia). It can cause significant discomfort and difficulty during eating. It is uncommon in dogs and cats but is very common in people who have undergone radiation therapy for tumors of the head and neck that resulted in collateral radiation injury to the salivary glands. As radiation treatment is used more commonly in veterinary medicine, xerostomia may become more frequent in animals. Decreased salivary secretion may also result from use of certain drugs (eg, atropine), extreme dehydration, pyrexia, or anesthesia. It is seen in some dogs with keratoconjunctivitis sicca and can be immune-mediated. Occasionally, it is due to disease of the salivary gland. Determination and treatment of the underlying cause is of primary importance. Physiologically balanced mouthwashes relieve the discomfort that results from xerostomia. Fluids should be administered if the animal is dehydrated. Immunosuppressive therapy is indicated if immune-mediated disease is suspected.