Gastroesophageal Reflux Disease in the Dog and Cat

Gastroesophageal Reflux Disease in the Dog and Cat 

Jinelle Webb, DVM, MSc, DVSC, Diplomate ACVIM 

Introduction

Gastroesophageal reflux disease (GERD) is a well-known phenomenon in human medicine, but it is likely underdiagnosed in veterinary medicine.1.2 It has been reported that gastroesophageal reflux occurs in up to 41% of asymptomatic dogs.' Little is known about gastroesophageal reflux in cats, but it likely occurs relatively frequently as well. Many challenges face the inclusion of GERD in a differential diagnosis list, and the steps to attain a diagnosis. There are often non-specific clinical signs present, or even no clinical signs at all. The underlying pathology that is causing GERD can be difficult, if not impossible, to definitively prove. Some of these difficult-to-prove causes include an intermittently ineffective lower esophageal sphincter, or delayed gastric emptying leading to prolonged periods of gastric distension. If a pathology is suspected that is leading to GERD, therapy to prevent esophageal reflux can also be a challenge. However, there are diagnostic steps that can be helpful in narrowing down the causes of GERD, and a therapeutic plan that can benefit affected pets. 

Anatomy and physiology 

The esophagus, stomach and duodenum require a coordinated muscular system, and effective sphincters (upper esophageal sphincter or UES, lower esophageal sphincter or LES, and pyloric sphincter), in order to cause the efficient and appropriate passage 

of ingesta. Dogs and cats have an esophagus and stomach oriented on a horizontal plane, in comparison to humans where the vertical position allows gravity to aid in the movement of ingesta from the mouth to the duodenum. However, there are certain aspects of human anatomy that predispose humans to GERD when compared to dogs and cats, such as the effect of gravity on thoracic organs causing pressure on the diaphragm, and the anatomic location of the pylorus in comparison to the fundus.3 

Ingesta should move rapidly through the esophagus and into the stomach; the esophagus is very sensitive to retained ingesta, or refluxed gastric and duodenal contents. Once ingesta has entered the stomach, coordinated gastric contractions then cause the breakdown of ingesta into smaller pieces, and the movement of the ingesta into the duodenum through the pyloric sphincter. The esophagus does have some barrier functions present to reduce the chance of damage from caustic substances, however these barriers are minimal when compared to the stomach. A properly functioning esophagus should not require the barriers needed in the stomach, which experiences a variation in pH not found in the esophagus. Gastroesophageal reflux is the retrograde movement of gastroduodenal contents into the esophagus. The presence of gastric and duodenal secretions in the esophagus can cause mucosal erosion and inflammation, which can extend into the submucosa and muscularis in severe cases

Causes of gastroesophageal reflux 

A common cause of gastroesophageal reflux is anesthesia induced relaxation of the LES, which occurs at a time when the pet is not conscious to react to the reflux of material.

Figure 1. A cat under general anes- thesia, with endoscopic visualization of a relaxed and partially open lower esophageal sphincter (LES). A small amount of yellow refluxed material can be seen. Picture kindly provided by the Internal Medicine service of the VCA Canada Mississauga-Oakville Veterinary Emergency Hospital, Oakville, ON 

Many pre-anesthetic and anesthetic agents are known to reduce the tone in the LES. When reflux occurs that is either occult or goes unnoticed, the extended exposure time of these caustic secretions during an anesthesia can result in mild to severe esophageal damage. However, this is a predictable cause of gastroesophageal reflux, and there are steps that can be taken to reduce the chance of its occurrence.

In the conscious patient, causes of GERD involve a lack of tone in the LES, prolonged periods of distension of the stomach, chronic vomiting or coughing, or disorders such as hiatal hernia. There does seem to be a link between GERD and airway disease, and GERD is considered one of several aerodigestive disorders. GERD is seen more frequently in brachycephalic dogs, which commonly have congenital and breed related respiratory disease 

Figure 2 An English Bulldog, showing typical brachycephalic anatomy. Picture kindly provided by Dr.Jen (Kyes) Websdale, DVM,

Prolonged periods of gastric distension can be caused by a delay in gastric emptying  

There are many causes of delayed gastric emptying. A physical obstruction to outflow through the pyloroduodenal junction will delay emptying, as will a reduction in gastric motility. Causes of delayed gastric emptying due to reduced motility include both gastric disease and systemic disease. Primary infectious and inflammatory gastric disease can result in delayed gastric emptying, as can systemic diseases that result in electrolyte disturbances, metabolic disorders, use of certain drugs, and abdominal inflammation.

Little is known about ineffective sphincters in the upper gastrointestinal tract. The sphincters themselves are created by alterations and/or thickening in focal areas. 

Aerodigestive disorders 

Aerodigestive disorders are diseases that affect both the respiratory and gastrointestinal affect both the respiratory and gastrointestinal systems, and many disease processes fall under this umbrella. However, it is only recently that a link was recognized between treatment of GERD, and improvement in certain respiratory diseases, both in animals and humans. In addition, addressing certain airway conditions can result in improvement in GERD, especially in brachycephalic dogs. 

Brachycephalic dogs are well known to have gastrointestinal disease, including poor gastric motility and pyloric hypertrophy, as well as brachycephalic syndrome affecting the upper respiratory system. One study indicated that in brachycephalic dogs previously treated medically for gastrointestinal symptoms, a definite and sustained improvement in gastrointestinal symptoms was noted in 88% of dogs after brachycephalic surgery. This same study also found that pre-surgical treatment for presumed GERD resulted in a decreased complication rate and improved prognosis in brachycephalic dogs undergoing brachycephalic corrective surgery. Another study has indicated increased incidence of GERD in dogs with laryngeal paralysis.

The pathophysiology causing a link between. GERD and respiratory disease is not fully elucidated. There is likely a component of partial lack of protection of the larynx in certain causes of dysphagia, as a highly co- ordinated process is needed for proper swallowing. However, there is no evidence to date that altered swallowing is present in all cases of GERD. More data is needed on the 

link between GERD and respiratory disease in the dog and cat; however, there should be an increased awareness of GERD in at-risk breeds, and the potential for improvement in GERD by addressing certain respiratory issues. 

Consequences of gastroesophageal reflux 

Exposure of the esophageal mucosa to caustic gastric and duodenal material can result in esophagitis and esophageal erosion. De- pending on the nature of the material, period of exposure, and presence of repeated exposure, this can vary from mild to severe esophagitis and possibly mucosal erosion. Damage to the esophagus in the conscious pet experiencing gastroesophageal reflux typically occurs in the distal aspect of the esophagus, and can be circumferential.

However, damage to the esophagus in the anesthetized cat or dog can involve the proximal esophagus, mid esophagus, distal esophagus, or entire esophagus, depending on where the refluxed material pools.

 Although not a common occurrence, a con- sequence of esophageal damage is the formation of an esophageal stricture. This is most likely to occur when there has been significant, circumferential damage. Fibrosis that is formed at areas of significant esophageal damage can lead to a stricture, which in many cases narrows the esophageal lumen to a tiny hole. These strictures may only allow the passage of liquid material such as water. The presence of regurgitated, undigested food within a very short period (seconds to minutes) after eating should raise concern for the possibility of an esophageal stricture. 

Clinical signs of gastro- esophageal reflux 

In many cases of dogs and cats with GERD, no clinical signs are noted. Clinical signs, when present, may be vague and difficult to narrow down to the esophagus. 

More obvious clinical signs include 

- Excessive salivation, regurgitation, pain on swallowing, extension of the head and neck, and avoidance of food. 

-Some pets may appear hungry, but be unwilling to eat. However, many of these clinical signs can be also attributed to other disease processes. The pain noted may be interpreted as neck pain or dental pain. Excessive salivation can be interpreted as nausea or secondary to dental disease. Regurgitation can be difficult to differentiate from vomiting in some cases. Food avoidance is common in many disease processes. 

Physical examination is typically normal in pets with gastroesophageal reflux. However, it is important to thoroughly investigate the oral cavity for signs of dental disease, rule out neck pain, and perform an abdominal palpation to assess for nausea or abdominal abnormalities. It may be helpful to offer food, and observe ingestion for any signs of pain when swallowing.

Diagnostics steps 

Definitive diagnosis of gastroesophageal reflux continues to be a challenge. The main goal when there is a clinical suspicion should be to rule out other causes, and obtain as much information as possible. Survey radiographs of the thorax and abdomen are likely to be normal in cases of GERD. Contrast radiography or fluoroscopy will likely also be normal, unless other diseases are present, or a hiatal hernia or esophageal stricture is present. Ultrasound of the thorax does not provide imaging of the esophagus, other than the proximal esophagus which is expected to be normal. 

Ultrasound of the abdomen is recommended, in order to rule out other disease processes, and assess for appropriate gastric emptying after a period of fasting. If delayed gastric emptying is documented, then causes of delayed gastric emptying should be investigated. This should include lab work (electrolytes at minimum, but ideally full lab work including random cortisol), fecal ova and parasite examination to rule out parasitism, and then upper gastrointestinal endoscopy to assess for outflow obstruction, and obtain biopsies to assess for inflammation and infection. Occasionally, delayed gastric emptying is idio-pathic and no cause is found. 

Upper gastrointestinal endoscopy can be helpful in some dogs and cats with GERD. The esophagus is a challenge to assess for motility under general anesthesia, as muscular contraction will not occur and therefore cannot be assessed. The esophagus can be evaluated for evidence of esophagitis, al- though many cases of GERD may only have intermittent esophagitis. Endoscopic biopsy of the esophagus is very challenging due to the muscular nature, unless there is relatively severe esophagitis present. In addition, there is variation in the pathologic interpretation of esophageal biopsies. The UES, LES, and pyloric sphincter are typically relaxed under general anesthesia, and therefore the presence of a relaxed and open sphincter does not indicate a pathologic process occurring when the pet is conscious. 

The primary goal of upper gastrointestinal endoscopy in pets with suspected GERD is to assess for possible causes, evaluate the gross appearance of the esophagus, stomach and duodenum, and obtain biopsies of the stomach and duodenum, especially in cases with delayed gastric emptying 

Occasionally, gastric parasitism is diagnosed endoscopically in cases when fecal parasite testing is negative. Esophageal stricture is easily diagnosed with endoscopy. When counseling owners on the goal of upper gastrointestinal endoscopy for cases of suspected GERD, it is important to remember that a normal gastrointestinal endoscopy does not rule out GERD. Many cases are diagnosed based on clinical suspicion, and therapy initiated to assess for a 

response. 

Future of diagnostics 

One of the biggest challenges facing increasing knowledge of GERD is the inability to fully assess the anatomy and function of the upper gastrointestinal tract. Efforts have been made to validate novel methods to assess swallowing and gastroesophageal motility in both humans and animals. Contrast fluoroscopy has the benefit of being performed on conscious pets, which eliminates any effect of sedation. However, there is a lack of standardization of interpretation of these studies, and a large variation of normal seen in pets. In addition, some abnormalities in function of the upper gastrointestinal tract are intermittent, therefore contrast fluoroscopy may be normal in a pet with GERD. The most promising diagnostic test to diagnose GERD in dogs and cats to date is measuring intraesophageally pH proximal to the LES, in the conscious pet and over a period of time. This immediately presents the issue of a conscious pet tolerating the placement of an esophageal catheter that can measure pH, and the pet allowing it to remain in place over time. These catheters have the benefit that they can measure pH impedance, which allows determination of composition of refluxed material, along with data regarding the movement of the refluxed material. However, keeping the catheter in place for even 24 hours is a challenge in conscious pets. Another option is the use of a capsule that is attached to the esophageal wall, which does not require a catheter and therefore is tolerated well by pets. The capsule can only measure pH, but can gather data for 96 hours (4 days). This method has promise in the diagnosis of GERD in pets, although the cost of placement under general anesthesia may dissuade many pet owners. In addition, the use of esophageal capsules has not been validated for dogs and cats, and there is the potential for complications such as early dislodgement or even capsule retention, as the capsule is intended to dislodge on its own after approximately 5-7 days.3 In some cases, data transmission does not occur consistently over the 96 hours. However, there is promise in at least increasing knowledge of gastroesophageal reflux in the dog and cat through study, using the capsule and/or catheter. 

Therapy 

Most cases of GERD will be diagnosed based on clinical suspicion, rather than a definitive diagnosis. However, cases where an underlying disease process is documented should have therapy targeted towards that disease process, along with consideration of what may be helpful to reduce 

gastroesophageal reflux. 

Diet manipulation is an important component of many gastrointestinal diseases, and this is the case for many causes of GERD. If an underlying disease process is present, then diet manipulation targeted to that disease should be selected. For example, evidence of inflammatory bowel disease may warrant a hypoallergenic diet. Diet texture can help with some disease processes. Improvement in transit times for cases with delayed gastric emptying may be seen by using lower fat, canned or liquified diets. This may be as simple as soaking kibble in water prior to feeding, allowing for a crumbled to slurry type diet. Frequency of feeding is also an area where manipulation may be of benefit. Feeding smaller meals more frequently can improve gastric transit times. Late night feeding of larger meals should be avoided in pets with proven or suspected GERD, as the LES may be more relaxed during sleep. 

There are several medications that may aid in the reduction of gastroesophageal reflux, including those that provide a barrier function, reduce gastric pH, and increase motility. If there is esophagitis and/or erosion present, then liquid sucralfate is an import- ant medication to provide a barrier which protects the damaged region of the esophagus from refluxed material. 

Gastric pH can be increased with H2 receptor blockers (eg ranitidine, famotidine) or proton pump inhibitors (eg omeprazole). Use of these medications would reduce the acidity of material refluxed from the stomach into the esophagus, and therefore reduce the potential for esophagitis. 

In cases where gastric motility appears to be reduced, a promotility agent can be used to reduce the amount of ingesta in the stomach. Promotility agents have little impact on esophageal motility. Metoclopramide is the most commonly employed promotility agent, although Cisapride is also used in some cases. Both of these drugs can increase LES sphincter tone. Ranitidine also increases gastric motility to some degree. 

Medication can usually rapidly resolve esophagitis and/or erosion unless it is severe or has led to stricture. However, as gastroesophageal reflux can occur with no clinical signs, it can be challenging to know whether medication is required on an ongoing basis. This would require repeat endoscopy to reassess for ongoing damage, and because reflux can be intermittent, even repeat endoscopy may not diagnose these occurrences. Cases with documented delayed gastric emptying may need a promotility agent long term. Clinicians will need to use their judgement for duration of and type of medical therapy indicated in cases of proven or suspected GERD. 

Prognosis 

The prognosis in pets with GERD is variable. It is somewhat dependent on the underlying cause of GERD, and the ability to correct or treat the cause. In cases where gastroesophageal reflux can be managed, ideally with correction of an underlying disease process, or through diet manipulation, the prognosis is good. Cases that have had severe esophagitis leading to stricture formation have a more guarded prognosis, which will depend on response to intervention of the stricture. 

Communication is imperative throughout the process of workup of cases with suspected GERD  it is a disease that can have vague symptoms, and a lack of conclusive diagnostic results. It is important to manage expectations from the first appointment. There is benefit to obtaining negative results, meaning normal results from a diagnostic test can help to narrow down the possible differential list. The results of each test should be discussed, including how these results have aided in progression of the diagnostic process. At the point when clinical suspicion of GERD is high, but attaining a definitive diagnosis is not possible. In these cases, a trial of diet manipulation and/or medication trial may be recommended, with close assessment of response to therapy. 

Conclusions 

GERD remains a frustrating disease in the cat and dog, presenting a challenge to clinicians in obtaining a definitive diagnosis. However, intervention in cases with proven or suspected GERD can often result in an improvement in clinical signs. Client understanding and professional communication is vital throughout the diagnostic and therapeutic process. Over time, research may provide better diagnostic testing for cases of GERD in the cat and dog. 

Information Provided by: 

Dr. Jinelle Webb obtained board certification with the ACVIM (Small Animal Internal Medicine) in 2005, and then started the Internal Medicine Service at the Mississauga-Oakville Veterinary Emergency Hospital. In 2020, Dr. Webb started VetLink Mobile Imaging, a mobile practice providing internal medicine imaging and diagnostic services to local veterinary clinics. She is an Adjunct Professor at the OVC, has been active with both AAHA and the ACVIM, and is a published author and speaker. 

References 

1. 

Harris R, Grobman M, Allen M, et al. Standardization of a videofluoroscopic swallow study protocol to investigate dysphagia in dogs. J Vet Intern Med 2017;31(2):383-93. 2. Muenster M, Hoerauf A, Vieth M. Gastro-oesophageal 

reflux disease in 20 dogs (2012 to 2014). J Small Anim Pract. 2017;58(5):276-283.