Antibiotic Responsive Diarrhoea

Signalment

• Common in young German Shepherd Dogs

Description

Antibiotic responsive diarrhoea (ARD) used to be termed as small intestinal bacterial overgrowth (SIBO). It is a sign of an underlying disease rather than a diagnosis. The aetiology and pathogenesis of this disease is unknown. Few studies have documented the scale of increase in bacterial numbers or whether the growth is responsible for the clinical signs.

ARD can be claasified as idiopathic or secondary. In cases of idiopathic ARD, the only consistent finding is response and remission on antimicrobial therapy. This has been found to be relatively common, but not exclusively, in young German Shepherd Dogs. This is suggested to be associated with IgA defiency or dysregulation, although the true underlying mechanism could be far more complex and numerous other hypotheses have been proposed. In contrast, there is usually an underlying intestinal disease in cases of secondary ARD. Diseases which affect any of the following functions of the intestines can cause secondary ARD:

• decreased gastric acid production
• increased small intestinal substrate
• partial obstructive disorders
• anatomical disorders
• motility disorders

The consequence of ARD are:

• interferance with fluid and nutritional absorption due to dysfunction of the enzymes located at the microvillous.
• disturbance in mucosal permeability.
• deconjugation of bile acids.
• hydroxylation of fatty acids.

Diagnosis

Clinical Signs

• Chronic small intestinal diarrhoea
• Weight loss
• Failure to thrive
• Vomiting
• Variable appetite
• Borborygmi
• Abdominal discomfort

If no localising findings are obvious, a full investigation is recommended. This includes a full routine haematology, biochemistry, urinalysis, faecal bacteriology and parasitologym diagnostic imaging and gastroduodenoscopy. Trypsin-like immunoassay (TLI) can be used diagnose exocrine pancreatic insufficiency (EPI)However, the findings are usually unremarkable in cases of idiopathic ARD. In these instances, a trial treatment with antimicrobial therapy is warranted. If these animals are responsive to the antimicrobial, but the clincal signs relapses upon withdrawal of treatment, a true idiopathic diagnosis can then be made.

Currently, the gold standard direct test for diagnosing ARD is duodenal juice culture. However, this is an expensive test and it is rarely availble. Indirect tests such as serum folate and cobalamin concentrations have been used to analyse the bacterial concetrations in small intestines. Some species of bacteria may increase the level of serum folate concentration or decrease serum cobalamin concentration, or both. Unfortunately, the sensitivity and specificity of this test is low and therefore have questionable use in the diagnosis of ARD.

No single diagnostic test is ideal or recommended for the diagnosis of idiopathic ARD. If secondary ARD is suspected, an investigation for the underlying cause is recommended.

Treatment

Idiopathic ARD

• Antimicrobial for an initial period of 4 weeks
  • A longer course may be required if the clinical signs relapse. This holds true for most cases of ARD.
  • Suitable drugs include oxytetracycline, tylosin, metronidazole. Oxytetracycline if the drug of first choice for idiopathic ARD but its use for secondary ARD is controversial. In addition, resistance is fast to develop with oxytetracycline. Tylosin and metronidazole may be more appropriate at targetting bacteria that are likely to be present in secondary ARD.

Secondary ARD

• Treatment of the underlying cause of ARD

Dietary modification

• Highly digestible and fat restriction diet, with added prebiotics
• This may be useful in both idiopathic and secondary ARD.

Prognosis

For cases of secondary ARD, the prognosis depends on the underlying cause and success of treatment. For cases of idiopathic ARD, the prognosis is guarded and many of them are likely to relapse when treatment is stopped, which may require a prolonged or life-long treatment. Some cases, however, do resolve and only require a short term treatment.

References

• Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company.
• Hall, E.J, Simpson, J.W. and Williams, D.A. (2005) BSAVA Manual of Canine and Feline Gastroenterology (2nd Edition) BSAVA
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.