Chronic diarrhoea is common in dogs. Diarrhoea is considered as chronic when it lasts for longer than 2-3 weeks, or if there are relapsing episodes of acute diarrhoea. Differential diagnoses for chronic diarrhoea are numerous (see figure 1).
Management of diarrhoea can be challenging and sometimes frustrating especially from an owner point of view. A thorough diagnostic approach (figure 2) and appropriate treatment are paramount.
History and physical examination (including evaluation of the body condition score, dehydration, pallor of the oral mucous membranes, abdominal palpation and rectal examination) are the first steps.
Haematology, serum biochemistry (including urea, creatinine, ALP, ALT, glucose, total solids, albumin, cholesterol), electrolytes, basal cortisol, cobalamin and Spec cPL (or Snap cPLi) often form part of the initial investigations. Trypsin like immunoreactivity can also be run, when there is a clinical suspicion of pancreatic exocrine insufficiency.
It is important to remember that the sensitivity of Spec cPL or Snap cPLi is around 80%, and thus a negative result does not rule out a pancreatitis.
Basal cortisol should be used as a screening test for glucocorticoid deficiency hypoadrenocorticism. This means that a value below 55nmol/L can be used to rule out the disease, but a lower value does not confirm hypoadrenocorticism, and in that case ACTH stimulation test is necessary. Specific electrolyte abnormalities (hyperkalaemia and hyponatraemia) can also raise a suspicion for Addison’s disease.
Initial evaluation (physical examination and bloodwork) may reveal an extra-digestive condition (hypoadrenocorticism, pancreatitis, pancreatic exocrine insufficiency, kidney disease, hepatopathy…). In that case specific investigations and treatment are appropriate.
Hypocobalaminaemia (<300ng/L) does not give an indication of the specific cause of the diarrhoea; however, it is more frequent in chronic enteropathy and alimentary lymphoma. Vitamin B12 supplementation is necessary in cases of hypocobalaminaemia, regardless of the origin of the diarrhoea.
Significant hypoproteinaemia can be due to protein-losing enteropathy (as a result of neoplastic or inflammatory infiltration of the intestinal wall, or lymphangiectasia). In that case further investigations including abdominal ultrasound, endoscopy and biopsies of the stomach and duodenum +/- ileum and colon are recommended. It is imperative to obtain intestinal biopsies and not just gastric biopsies in dogs with suspected chronic enteropathy.
Chronic intestinal bleeding (in some cases not witnessed by the client) can cause hypochromic, microcytic anaemia and thrombocytopaenia or thrombocytocytosis. In that case, ultrasonography and gastroduodenoscopy would be recommended.
When there is no sign of an extra-digestive condition or systemic consequences (such as hypoalbuminaemia or anaemia), and if the patient is otherwise clinically stable various treatments can be tried, in the following order:
Intestinal parasites (helminths, protozoa) can contribute to chronic diarrhoea, even if the dog is regularly wormed. Faecal examination (on faeces collected during 3 days as many parasites have intermittent excretion) can be performed before starting treatment. Fenbendazole (50mg/kg once a day for 5 days) is recommended due to its broad spectrum of activity.
If there is no improvement, a diet trial can be trialled at this stage or alternatively further investigations can be started. The dog needs to be fed exclusively with a hypoallergenic diet or with a diet containing a single protein source.
Finally, if after 2 weeks of strict diet trial the clinical signs don’t resolve, options include further diagnostics or an antibiotic course. Metronidazole is often the antibiotic of choice (10mg/kg twice a day) for 2 weeks minimum due to its purported gastrointestinal immunomodulatory effects.
When there is no evidence of extra-digestive conditions, and diarrhoea does not respond to previously described trials; or when there is poor body condition, abnormal abdominal palpation, melaena, hypoproteinaemia or anaemia present. Many clients prefer to pursue further diagnostics prior to performing diet or drug trials.
Abdominal ultrasonography may reveal a foreign body, an abdominal mass, thickening of the intestinal wall, an abdominal effusion… and these findings may then orientate the further diagnostics.
Often, upper +/- lower digestive endoscopy are indicated. This allows direct visualisation biopsy sampling of the intestinal wall.
Histological analysis of intestinal biopsies may reveal chronic enteropathy, lymphangiectasia, neoplasia… A specific treatment will then be elected, including possibly another diet trial, immuno-suppressive therapy or chemotherapy.
Faecal culture is uncommonly recommended, for two reasons: bacterial diarrhoea in dogs is uncommon, and the presence of pathogenic bacteria in a canine faecal sample does not necessarily mean that this bacteria is causing the clinical signs.
However, if all the previously described procedures did not reach a diagnosis, or if there are immune-suppressed persons in the household and the risk of a zoonosis is a concern, faecal culture could be done. Pathogenic E.Coli, Salmonella, Campylobacter, Yersinia and Clostridium (difficile and perfringens) are the most common bacteria involved in canine bacterial diarrhoea.
Thorough workup is paramount in the management of chronic diarrhoea. The owners have to be aware that it can be difficult to find a diagnosis, and further investigations are often necessary. They have to be involved in the management of the disease, as this is likely to increase the chances of therapeutic success.