Dysphagia is painful or difficulty in swallowing, originating from disorders of the oral, pharyngeal, cricopharyngeal, esophageal, or gastroesophageal stage of swallowing, causing ptyalism, dropping food from mouth, gagging, or multiple swallowing attempts with a single bolus of food. Animals with disorders of the oral cavity, tongue, or jaws have difficulty with the prehension and mastication of food. The affected animals may modify their eating behavior by tilting or throwing back the head while eating. With oropharyngeal and cricopharyngeal disorders, animals will immediately eject a food bolus (undigested) and will display multiple attempts to swallow, generally accompanied by flexing and extending the neck. The swallowing may be painful and drinking ability may also be affected. The animal may cough due to either saliva or food retained within the pharynx or related to the aspiration of food into the airways. Esophageal and gastroesophageal dysphagia typically results in regurgitation of undigested food (see Chapter 27). Discussion in this chapter will be limited to oropharyngeal dysphagia.

Swallowing requires a complex series of well-coordinated events in order to move a bolus of food from the oral cavity to the stomach. Cranial nerves V (trigeminal—masticatory muscles), VII (facial–facial muscles), IX (glossopharyngeal–pharyngeal muscles), X (vagus—pharyngeal and esophageal muscles), and XII (hypoglossal—tongue movement) innervate the numerous muscles used during the act of swallowing.

The normal swallowing sequence can be divided into three phases: (1) oral, (2) oropharyngeal, and (3) cricopharyngeal. The oral stage includes uptake of food or liquid by the tongue, teeth, and/or lips. During the oral stage, the bolus is accumulated at the base of the tongue. Rostral to caudal pharyngeal contractions then propel the bolus from the base of the tongue to the cricopharyngeal passage (pharyngeal phase). The cricopharyngeal stage consists of the relaxation of the cricopharyngeal sphincter, passage of the bolus into the cranial esophagus, closure of the upper esophageal sphincter, and relaxation of the pharyngeal muscles.

The esophageal phase begins when food enters the esophagus. Both primary and secondary peristaltic waves move the bolus of food toward the stomach. The final phase is the gastroesophageal phase, during which the lower esophageal sphincter relaxes and the bolus passes into the stomach.

History and Physical Examination

It is critical to distinguish between the different types of dysphagias as treatment options and prognoses are different. Obtaining a detailed history and observing the animal’s eating and drinking can be helpful in localizing the cause of dysphagia. Careful palpation of the structures of the head and cervical region may reveal a mass or evidence of trauma. The oral cavity should be visually examined and a neurologic examination, including gag reflex, is a must. Rabies is a potential cause of dysphagia. This disease should be carefully considered and the examination procedures modified to reduce human exposure. Younger animals, especially if the dysphagia begins after weaning from milk to solid food, are more likely to suffer from congenital defects. An acute onset of dysphagia in a young to middle-aged dog is most consistent with a foreign body or ingestion of a caustic substance. In older animals with dysphagia, the presence of multiple cranial nerve defects suggests central nervous system involvement. Animals with other body system abnormalities (vomiting, weight loss, and diarrhea) along with dysphagia have an increased likelihood of systemic disease.

Diagnostic Plan

Survey radiographs of the head and neck are indicated if a mass or foreign body is suspected. Thoracic radiographs (including both laterals) are required if aspiration pneumonia or a neoplastic process is suspected. Hematology, biochemical profile, and urinalysis should be done to rule out associated diseases or if other systemic signs are present. With functional disorders, such as cricopharyngeal achalasia, contrast fluoroscopy motion study is recommended. A barium swallow must be done using different consistencies—liquid, paste, and solids (barium-coated kibble). Special care is needed for animals when aspiration is likely. Additional serologic testing should be performed as needed, for example, acetylcholine receptor antibody titers for myasthenia gravis and thyroid testing for a neuropathy secondary to hypothyroidism. An oral examination under sedation and/or endoscopy may be needed.