Problem refinement

Irritable bowel syndrome, IBD and coeliac disease do show over-lapping symptom profiles, so to differentiate between these conditions you need to know more about the diarrhoea, if Simon experiences other symptoms and if anything aggravates/precipitates or ameliorates his symptoms. 

Simon tells you that he experiences bloating and lower abdominal discomfort during episodes of diarrhoea. He reports not seeing any blood in the diarrhoea and generally feels fit and healthy both in between and during the episodes of diarrhoea. He has not noticed anything that seems to worsen or help his symptoms.

This description best fits with IBS. In coeliac disease, one would expect Simon to show fatigue and weight loss, while IBD patients usually report symptoms impacting on normal activities, which include bloody diarrhoea, urgency and non-GI symptoms, such as fatigue and joint pain.

Before deciding on management, it would be prudent to check about a medicine history as it is well-known that many medicines can cause diarrhoea. Simon takes occasional ibuprofen – known to cause diarrhoea – but does not believe that his symptoms coincide with taking it. He has previously had no problems with the analgesic, use of which pre-dates his current symptoms. You arrive at a differential diagnosis of IBS.

Red flags

We know Simon has not reported alarm symptoms of weight loss or fatigue (associated with colorectal cancer and Addison’s) or blood in the stools/rectal bleeding, which are associated with colorectal cancer. Simon also shows no signs associated with classical diabetes presentation such as polyuria or polydipsia. 

Management

Simon should be given general advice on nutrition – for example, keeping adequately hydrated, eating regular meals and adjusting fibre intake. Simon could buy loperamide to manage the diarrhoeal episodes.

Regarding prescribing options, antispasmodics are generally first-line in managing abdominal pain/spasms (e.g. mebeverine, alverine or peppermint oil). Second-line treatments include low-dose tricyclic antidepressants (TCAs), such as amitriptyline at a dose of 5-10mg at night, increasing the dose to a maximum of 30mg.
However, given Simon’s symptoms, the use of such agents does not seem warranted.

Safety netting

You tell Simon you think he has IBS and that treatments are available to manage the problem of flare-ups. A follow-up appointment should be made within the next two months to assess his symptoms and consider if any further interventions are required. You also tell him if symptoms worsen or he notices any blood in his stools, he needs to come back straightaway.