Overlap of functional dyspepsia (FD) and irritable bowel syndrome (IBS) might be more common than expected and associated with more severe symptoms, according to Australian research.

A study of more than 1,000 consecutive gastroenterology outpatients at the Princess Alexandra Hospital in Brisbane found more than 10% of patients had a functional gastrointestinal disorder.

On clinical diagnosis 59% had IBS, 17.5% had FD and 23.3% had an overlap of FD and IBS.

However when categorised using the Structured Assessment of Gastrointestinal Symptoms Scale (SAGIS), many patients were re-allocated – resulting in 29.2% with a diagnosis of IBS, only 6.7% with FD and 64.2% with overlap.

The study found a higher intensity of symptoms was likely to predict overlap.

“90% of patients in the high IBS symptom intensity group, and 95% of patients in the high FD symptom intensity group had an overlap of both disorders,” the study said.

The implications of FD and IBS overlap for the long-term outcome of patients and the response to therapies needs to be further explored, the researchers concluded.

Co-author Professor Nick Talley, from the University of Newcastle, told the limbic that the evidence regarding functional gastrointestinal disorders was evolving.

“And these findings indeed support our working hypothesis that these two sets of problems have a similar underlying set of mechanisms. We have been working hard on finding those causes and we are starting to unravel those. We think the small intestine is very important in both stomach type symptoms, interestingly, as well as in colon type symptoms.”

“We know some of these people, in fact probably many of them, have a subtle inflammation in their intestines and we think that when you have more extensive inflammation you get the overlap and you have more severe symptoms.”

“There’s a lot we don’t know but indirectly looking at blood markers of intestinal inflammation – circulating small bowel homing T cells – they are elevated in both of these conditions.”

He said clinicians often fail to ask the questions that might help with recognition and tailor management of the FD and IBS overlap.

“Don’t forget to ask about dyspepsia symptoms in people with IBS routinely because it might modify their management.”

He added there was some evidence that some current therapies may help both types of symptoms.

“So a low FODMAP diet may help both IBS and dyspepsia in some cases. And certain medications may help both as well.”