Do you need an endoscope to diagnose canine gastrointestinal diseases?

As an RCVS Recognised Specialist in Small Animal Medicine (Gastroenterology), I am never happier professionally than when undertaking gastrointestinal (GI) endoscopy - even colonoscopy where the challenge now is to obtain ileal biopsies. But I am strange like that!

Vomiting and diarrhoea are common presenting problems in small animal practice but they are only clinical signs and not the diagnosis. Whilst they may be an indication of primary GI disease, they can also be caused by a large number of extra-GI conditions.

Concentration of investigations on the GI tract (including endoscopy) too early in the diagnostic approach may lead to unnecessary tests being performed and can result in an erroneous diagnosis with, at worst, fatal consequences. However, through careful history-taking and thorough physical examination, with particular emphasis on all body organ systems, the clinician should avoid such errors. 

Only after disease in other organ systems has been evaluated and ruled out is it safe to formulate a diagnostic plan for the investigation of GI disease - which need not necessarily include endoscopy and endoscopic biopsy.

Should your diagnostic plan include endoscopy?

Many years ago I was in the middle of investigating megaoesophagus in a Westie, when I got the lab results back showing hyponatraemia and hyperkalaemia. An ACTH stimulation test confirmed hypoadrenocorticism and saved the dog from more unnecessary investigations, but didn’t hide my embarrassment.

Now, having acquired the necessary equipment and skill after years of practice, I have become increasingly aware that endoscopy is often not needed to make a diagnosis in many situations. This is good news if your practice cannot afford an endoscope, or only has one that is the wrong size for a Chihuahua or a Great Dane!

Whilst endoscopy can provide a definitive diagnosis of certain conditions, it often only confirms what the astute clinician has already identified through the key skills of history-taking, physical examination, laboratory testing and imaging. It cannot diagnose non-GI causes of the signs, and if a histological diagnosis of GI inflammation is made, the clinician still has to find the cause; they may even resort to empirical treatment trials, as inflammation is merely a final common pathway for a number of underlying causes.

There is virtually no indication for endoscopy in acute GI disease, which is almost always self-limiting if the patient is treated supportively. And only when there are criteria of concern such as anorexia, severe weight loss, and hypoalbuminaemia should endoscopy be considered in cases of chronic diarrhoea.

The young puppy with chronic diarrhoea that is still eating, is most likely to have a dietary or infectious cause once an intussusception is ruled out by palpation and/or imaging. Endoscopic biopsy is very likely to yield absolutely nothing significant: idiopathic inflammatory bowel disease (IBD) is not a disease of puppies. So why not look for and treat any infections and perform a diet trial before ever considering endoscopy in such cases?

Last year I was asked to perform endoscopy on a colleague’s dog that had a presumptive diagnosis of IBD and a secondary reactive, immune-mediated polyarthritis but was not responding as expected to steroids. The answer was obvious when I saw Uncinaria hookworms in the duodenum. And the dog’s sore limbs weren’t due to polyarthritis but interdigital larval migration. A faecal examination confirmed the diagnosis, but this examination (or empirical worming) should have been done first as endoscopy was not needed.