Introduction

Easier access to endoscopic examination of the upper gastrointestinal tract has led to a marked improvement in the diagnosis of esophageal, gastric and small intestinal diseases. However, the increased use of endoscopy in dogs with suspected inflammatory bowel disease (IBD) led to the problem that the histology of mucosal biopsies often does not bring the expected diagnostic yield.

The most commonly used endoscopic technique is standard push enteroscopy with biopsies of the gastric and duodenal/jejunal mucosa. Endoscopy has also been increasingly useful to perform minimally invasive therapeutic procedures. Endoscopic techniques rarely used in veterinary medicine are capsule and double balloon enteroscopy, and endoscopic retrograde cholangio-pancreatography (ERCP).^1-5 ERCP, a combination of endoscopy and radiology, has shown to increase the value of endoscopy for the diagnosis and treatment of pancreatic and biliary tract diseases in people and dogs.^4,5

Indications for Diagnostic Endoscopy

Diagnostic standard push enteroscopy aims at the differentiation of inflammation, neoplasia and anatomic anomalies to support treatment decisions, and assess prognosis and outcome. Diagnostic tools that help to decide for or against endoscopy include clinical assessment of disease severity, response to previous empirical treatments, results of laboratory tests, and findings of noninvasive imaging techniques (thoracic and abdominal radiology, abdominal ultrasound).

Clinical Signs

Clinical signs suggested as indications for endoscopy of the upper gastrointestinal tract are regurgitation, esophageal/gastric foreign body, chronic or recurrent vomiting, hematemesis, melaena and chronic or recurrent small intestinal diarrhea.

Regurgitation, Chronic Vomiting and Hematemesis

These signs without evidence of coagulation disorders have a high likelihood of endoscopic findings. Esophageal diseases that are easily diagnosed endoscopically are foreign body, esophagitis, stricture, parasitism (Spirocerca lupis in endemic areas) and neoplasia. Megaesophagus is rather a radiologic diagnosis and can be misdiagnosed using endoscopy due to the possible relaxation of esophageal striated muscles during deep anesthesia. However, endoscopy can help to differentiate primary (idiopathic) from secondary megaesophagus caused by esophagitis or neoplasia at the lower esophageal sphincter. In case of chronic vomiting and hematemesis, endoscopy helps to reveal different types of chronic gastritis, gastric foreign body and neoplasia.

Melaena

This clinical sign of upper gastrointestinal tract bleeding indicates standard push enteroscopy especially when the patient has also hematemesis. However, endoscopy is nondiagnostic when the lesion is in a part of the small intestine that cannot be reached by endoscopy. Capsule and balloon enteroscopy allow the search for intestinal bleeding by investigating the whole small intestine. However, both techniques are currently not available in veterinary medicine.^1-3 Diagnostic laparotomy is currently the only alternative to diagnose causes of jejunal bleeding.

Chronic or Recurrent Small Intestinal Diarrhea

This can be caused by primary intestinal diseases or disorders that secondarily affect intestinal function. Endoscopy of the small intestine is indicated when inflammatory bowel disease (IBD) is suspected since the diagnosis 'IBD' is based on histologic confirmation of benign intestinal inflammation in patients with 1) persistent gastrointestinal signs, 2) failure to document other causes of gastroenterocolitis by thorough diagnostic work up, and 3) failure to respond to symptomatic therapies (anti-parasitics, antibiotics, gastrointestinal protectants).⁶

The clinical assessment of disease severity in dogs with suspected IBD is currently performed by calculating the canine IBD activity index (CIBDAI) or the canine chronic enteropathy clinical activity index (CCECAI).^7,8 A feline IBD (FIBD) index was also prospectively evaluated in a limited number of cats.⁹ Whether the CIBDAI, CCECAI and FIBD-index can also be indicators for endoscopy remains debatable. In contrast to an initial report that the CIBDAI correlates well with histology,⁷ recent studies did not find this correlation.^8,10,11 However, high CIBDAI scores can be seen as an indication for intensifying the diagnostic workup, especially when the patient does not respond to empirical treatment, laboratory results suggest systemic effects of the intestinal disease, or imaging techniques reveal no other possible pathologic background.

No response to empirical treatment is another indication for direct macroscopic and histologic examination of the small intestine. It has been reported that 50-70% of dogs with chronic enteropathies respond to diet change alone.^8,11,12 It has also been repeatedly documented that food responsive enteropathies cannot be differentiated by histology from steroid responsive enteropathies.^8,11 Therefore it seems reasonable that dietary management should precede endoscopy. When dietary change (e.g., hypoallergenic diet) and immunomodulatory antibiotics (e.g., tylosin, metronidazole) has failed, it seems reasonable to expect a higher likelihood of endoscopic findings that influence further treatment decisions.

Currently, endoscopic control examinations of dogs with IBD seem to be of academic value only. In clinical practice they are probably not always indicated. Several articles reported that histological changes in the small intestine did not improve even when patients showed significant improvement in the clinical CIBDAI score with dietary and medical treatment.^8,11,13

Laboratory Tests

Laboratory tests play an important role in assessing systemic effects of the disease process and the necessity for intensified diagnostic workup. Useful parameters are serum total protein, albumin, and cobalamin. Serum C-reactive protein (CRP) and fecal alpha1-antiprotease are also suggested to be of value.

Panhypoproteinemia and hypoalbuminemia are associated with a poorer prognosis and the necessity for more intensive medical treatment.^8,10,12,14 Therefore, low serum protein levels strongly indicate macroscopic and histologic examination of small intestinal tissue. Endoscopy is a favorable alternative to diagnostic laparotomy with intestinal full-thickness biopsy, because endoscopy caries fewer risks for complications in severely hypoproteinemic patients.¹⁵

Low serum cobalamin values indicate the need for endoscopy when exocrine pancreatic insufficiency has been excluded by determination of serum cTLI or canine fecal elastase. Hypocobalaminemia is a negative prognostic sign since it reflects long lasting malabsorption.^8,12

Serum concentration of canine CRP could be useful as an activity marker of canine chronic enteropathies as one study suggests.⁷ However, other studies did not find a correlation between clinical severity index (CIBDAI) and cCRP concentration.⁸ In human medicine, CRP values correlate well with the activity of Crohn's disease but not as well with ulcerative colitis.¹⁶

Fecal markers that are promising indicators to detect gut inflammation in patients with established IBD are calprotectin and alpha1-proteinase inhibitor.^17-19 Increased fecal alpha1-PI concentration may signal the need to perform gastrointestinal biopsies.²⁰

Non-invasive Imaging Techniques

Techniques such as radiography and abdominal ultrasound are helpful tools to decide whether endoscopy or surgery should be chosen as next step of the diagnostic work up or treatment. Esophageal and gastric foreign bodies are an indication for endoscopic intervention; intestinal foreign bodies still need a surgical approach.

Standard push enteroscopy is indicated when abdominal ultrasound reveals intestinal hyperechoic mucosal striations in a hypoproteinemic patient. The finding is associated with lymphangiectasia but does not predict the histologic severity.^21,22 In dogs with suspected IBD, ultrasonographic exclusion of intestinal wall changes does not exclude the presence of IBD.²³ Laparotomy with full-thickness biopsies of the intestinal wall is indicated when ultrasound reveals marked thickening, irregularity, and loss of structure of the intestinal wall. These sonographic findings are strongly associated with neoplastic processes.^24-26

Indications for Therapeutic Endoscopy

Endoscopic therapeutic procedures are indicated when the minimal invasive approach ensures a successful alternative to surgical methods. Possible endoscopic interventions in the upper gastrointestinal tract are removal of foreign bodies out of esophagus and stomach, dilation of esophageal strictures, and placement of tubes for enteral feeding such as percutaneous gastric (PEG) tubes, and PEG-jejunal or nasojejunal tubes for postduodenal feeding.^27,28 Endoscopic sphincterotomy of the major papilla by ERCP might be a useful alternative to surgical treatment of extrahepatic biliary obstructions in future.⁵

References

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