Cricopharyngeal achalasia in a dog

Abstract

A 4-month-old, female terrier-poodle cross was presented with a chronic history of dysphagia. Fluoroscopic swallowing studies localized the problem to the upper esophageal sphincter. A diagnosis of cricopharyngeal achalasia was made. After cricopharyngeal and thyropharyngeal myectomy, the dog was able to eat soft food without difficulty.

A 4-month-old, female terrier-poodle cross with a history of chronic dysphagia was referred to the Western College of Veterinary Medicine for further diagnostic tests and treatment. On physical examination, the dog appeared bright and alert, but she was thin and small for her age. Lung sounds were increased bilaterally. The referring veterinarian was suspicious of aspiration pneumonia, so the dog was being treated with amoxicillin/potassium clavunate (Clavomox tablets; Pfizer Animal Health, Kirkland, Quebec), 8 mg/kg bodyweight (BW), PO, q12h.

Results of a complete blood cell (CBC) count showed a mild lymphocytosis (8.848 × 10⁹/L; reference range, 1.2 to 5.0 × 10⁹/L), due possibly to either the struggle during blood collection or antigenic stimulation. Results of a biochemical panel showed an elevation in alkaline phosphatase (128 mmol/L; reference range, 9 to 90 mmol/L) and phosphorus (2.50 mmol/L; reference range, 0.63 to 2.41 mmol/L), likely due to the dog's young age. Creatinine was low (39 μmol/L; reference range, 41 to 121 μmol/L), associated possibly with her thin body condition and decreased muscle mass. There was also a mild hypercholesterolemia (6.10 mmol/L; reference range, 2.70 to 5.94 mmol/L).

Plain view cervical and thoracic radiographs were taken and a fluoroscopic swallowing study was performed. The cervical and thoracic radiographs showed no obvious abnormalities and, at the time, there was no evidence of aspiration pneumonia. Multiple fluoroscopic examinations were made with different types of food mixed with barium (Polibar; Therapex, Montreal, Quebec). On visual examination, the dog was observed to extend her neck and make multiple attempts to swallow. Gagging and coughing often followed this behavior. The fluoroscopic images showed that the pharynx became distended with food material and appeared to contract. Further movement of food was restricted at approximately the level of the upper esophageal sphincter (UES). Eventually, small boluses formed, entered the esophagus, and traveled normally to the stomach. A diagnosis of cricopharyngeal achalasia (CPA) was made.

Two days following the diagnosis, the dog was prepared for surgery. She was fasted overnight; the following morning, she was premedicated with glycopyrrolate (Sabex, Boucherville, Quebec) 0.01 mg/kg, BW, IM, and oxymorphone (Numorphan; Bristol-Myers Squibb Canada, Montreal, Quebec), 0.06 mg/kg BW, IM. She was then induced with ketamine (Betalar; Betrepharm, London, Ontario), 5 mg/kg BW, IV, and diazepam (Vallium; Sabex, Boucherville, Quebec), 0.5 mg/kg BW, IV, and maintained on isoflurane (IsoFlo; Abbott Laboratories, Saint-Laurent, Quebec).

A cricopharyngeal and thyropharyngeal myectomy was planned to relieve the constriction at the level of the upper esophageal sphincter. The dog was placed in right lateral recumbency and an incision was made on the left lateral side of the neck, slightly dorsal to the ventral midline. The musculature overlying the larynx and trachea was separated and retracted. The larynx and trachea were rotated ventrally; a suture was placed though the lamina of the thyroid cartilage to maintain laryngeal rotation, allowing for exposure of the cricopharyngeal musculature and cranial part of the esophagus. A bougie tube was passed into the esophagus to aid in identification of the esophageal wall. The m. cricopharyngeus and a portion of the m. thyropharyngeus were carefully elevated from the underlying esophagus, resected, and removed. Hemorrhage was minimal and controlled with gauze and light pressure. The esophagus was inspected for damage; none was seen. The suture in the thyroid cartilage was released and a routine 3-layer closure was performed with 3-0 polydioxanone suture (PDS II; Ethicon, Peterborough, Ontario). Dexamethasone (Dexamethasone 5; Vetoquinol, Lavaltrie, Quebec), 1 mg/kg BW, IV, and oxymorphone (Numorphan; Bristol-Myers Squibb Canada, Montreal, Quebec), 0.05 mg/kg BW, IM, were administered postoperatively.

The recovery from anesthesia was uneventful, and less than 24 h after surgery, the dog was able to eat soft food comfortably and without distress. Three months after surgery, she was doing well and showed no signs of dysphagia.

Cricopharyngeal achalasia occurs when the UES fails to relax or when there is asynchrony between contraction of the pharynx during swallowing and relaxation of the UES (1,2). For the purpose of this discussion, the term achalasia has been used to encompass both presentations. Cricopharyngeal achalasia is an uncommon condition in dogs, but it should be considered as a differential diagnosis in cases of dysphagia and regurgitation. It is considered to be a neuromuscular motility disorder in which there is asynchronous or incomplete relaxation of the UES (1,2,7,8,10). Cricopharyngeal achalasia is differentiated from other disorders of deglutition through the use of fluoroscopic swallowing studies (7,12). Several causes of CPA have been set forth. Early studies suggested that the cause might be due to cricopharyngeal hypertrophy or myositis (1,9). However, histopathological evaluation of affected m. cricopharyngeus in young dogs disputes this claim (10). The current belief is that there is an underlying congenital neuromuscular defect (8,11). The most common signalment of CPA is the development of dysphagia shortly after weaning, which lends anecdotal support to the theory of a congenital abnormality. A case study by Weaver (9) suggested a genetic predisposition for this condition in cocker spaniels.

Dogs with CPA generally present with a history of difficulty in swallowing, gagging, regurgitation, and nasal discharge. Aspiration pneumonia may occur as a sequela. Despite a ravenous appetite, the dog is usually small for her/his age. In the absence of aspiration pneumonia, other diagnostic parameters are normal. Clinical signs are not useful in differentiating between cricopharyngeal dysphagia and pharyngeal dysphagia. An accurate diagnosis of the cause of dysphagia is necessary, as surgical transection of the m. cricopharyngeus in dogs suffering from pharyngeal dysphagia will cause their condition to worsen. Radiographic evaluation is essential in diagnosing CPA.

Video fluoroscopy is the most reliable method of evaluating the complex process of swallowing (12). Survey radiographs and barium contrast studies only allow for the visualization of a single moment in the swallowing process, and thus are inadequate in providing information about motility. Swallowing has been divided into 3 phases: the oropharyngeal, esophageal, and the gastroesophageal phases (13). Obviously, much overlap exists between each of these stages, thus the division is not as straight-forward as it seems. The oropharyngeal phase, which is involved in CPA, is further divided into the oral, pharyngeal, and pharyngoesophageal stages (13). The oral phase involves prehension, and movement of the food bolus to the base of the tongue. Disorders of this phase are characterized fluoroscopically by decreased tongue movements and difficulty in accumulating a bolus (13). The pharyngeal stage of swallowing involves delivery of the bolus from the oropharynx to the laryngopharynx (13). Pharyngeal stage disorders are characterized by the presence of weak or absent contractions in the pharyngeal area seen during fluoroscopy (13). The m. cricopharyngeus, however, functions normally (13). During the pharyngoesophageal stage, the upper esophageal sphincter relaxes and allows the passage of the bolus into the cranial esophagus (13). Disorders seen during this phase vary, depending on whether the underlying problem is asynchrony or achalasia at the level of the cricopharyngeal musculature. On fluoroscopic evaluation, this may present as either contrast material being misdirected rostrally, in the case of asynchrony of pharyngeal contraction and cricopharyngeal relaxation, or pharyngeal contraction distorting the shape of the cricopharyngeal region, in the case of achalasia (13). Differentiating pharyngeal and cricopharyngeal dysphagia is pivotal to treatment, as the conventional treatment of cricopharyngeal dysphagia is surgery. If, however, the dysphagia is of pharyngeal origin, surgery will worsen the condition and increase the likelihood of aspiration pneumonia. The conventional treatment of this disorder is either the transection or the complete removal of the muscles that surround the esophagus in this region; specifically the m. cricopharyngeus, the m. thyropharyngeus, or both (4,5,6,7,14,17,18).

Several different surgical methods have been described for the resolution of CPA. Most approaches involve placing the dog in dorsal recumbency and making a ventral midline cervical incision (3,4). The larynx and trachea are rotated so as to expose the dorsal aspect of the cricopharyngeal musculature. An inflated Foley catheter or endotracheal tube can be place in the esophagus to aid in the identification of muscle fibers. The m. cricopharyngeus is then carefully elevated and removed by cutting the muscle along its lateral attachments. Other investigators have felt that transecting rather that removing the m. cricopharyngeus has been sufficient in resolving CPA (2,7). Another variation is to transect a portion of the m. thyropharyngeus as well (16,17).

An alternate approach is to place the animal in right lateral recumbency and make a left lateral incision dorsal to the larynx and ventral to the jugular vein, starting at the rostral aspect of the cricoid cartilage (6,14). Upon identification of the m. cricopharyngeus, it can be undermined and a portion resected. This approach has been described as technically easier to perform, allowing for more rapid identification of the m. cricopharyngeus (6). Complications arising from both of these surgical procedures include fibrosis, recurrent laryngeal paralysis, esophageal perforation, recurrence of dysphagia, and pharyngocutaneous fistula (14). Care must be taken to transect all muscle fibers or excessive fibrosis and recurrence of dysphagia may occur. In addition, if there is a concurrent pharyngeal component to dysphagia or if esophageal motility is impaired, there is an increased risk of aspiration pneumonia.

In humans with CPA, the diagnosis and treatment is very similar. There has been some investigation into the use of botulinum toxin for the diagnosis and management of CPA (17,18); however, surgery is still the preferred treatment, if the patient is a stable operative candidate.