Interstitial Cystitis

Why a Bladder Condition Shows Up in Stool Samples

The research here is early and the studies are small, but the pattern they point to is a surprising one. Interstitial cystitis, also called bladder pain syndrome, causes persistent pelvic pain, urgency and frequent urination without an infection to explain it. Treatment options are limited and the cause remains unknown. The clearest bacterial signal found so far isn't in the bladder at all.

Looking in the obvious place first

Urine was long assumed to be sterile. Better culture techniques showed it isn't, and the bladder holds its own resident bacterial community.

That made the bladder's own bacteria the obvious suspect, and several groups went looking.

The results didn't hold up. Two studies reported an association, but several others failed to find one, including a large multi-centre research programme set up specifically to study chronic pelvic pain.

The vaginal microbiome was examined too, with the same outcome. No consistent association emerged.

So the straightforward explanation, that a bladder condition is driven by bladder bacteria, hasn't survived testing.

The signal that did appear

Researchers then examined stool instead, on the reasoning that pelvic organs share sensory nerve pathways and animal work had shown gut bacteria altering pelvic pain.

They sequenced stool from 17 women with the condition and 17 healthy women, and scored symptom severity with a validated pelvic pain questionnaire.

Twenty-six bacterial groups passed a strict relevance threshold, spread across several distinct branches of the bacterial family tree.

Several were then confirmed with species-specific testing and described as deficient in this condition. They included Faecalibacterium prausnitzii and Odoribacter splanchnicus, both major producers of butyrate, the compound gut bacteria make from fibre that helps regulate inflammation and pain signalling.

The amounts tracked with how severe symptoms were, not just with having the diagnosis.

Source: Stool-based biomarkers of interstitial cystitis/bladder pain syndrome

How a gut signal could reach the bladder

An association between stool bacteria and bladder pain needs a route, and two plausible ones exist.

The first is nerve wiring. Sensory nerves from the bladder, bowel and other pelvic organs converge on the same segments of the spinal cord. Signals from one organ can amplify perception from another, which is why bowel and bladder symptoms so often travel together.

The second is inflammation. The bacteria found depleted here produce compounds that restrain inflammatory signalling throughout the body. Less of them means more of that signalling reaching tissues including the bladder wall and the nerves supplying it.

Neither route has been demonstrated in people with this condition. Both are consistent with what's been measured.

Where the evidence currently sits

Two limits are worth stating.

Seventeen people per group is small. Findings from studies that size need replication before anyone treats them as settled, and the specific bacteria named have varied between research groups.

Direction is also unresolved. Chronic pain changes diet, sleep, activity and medication use, all of which reshape gut bacteria. So the differences could partly follow the condition rather than contribute to it.

Genetic analyses published more recently have started testing whether specific gut bacteria causally influence risk, which is the approach most likely to settle it.

Source: The microbiota in patients with interstitial cystitis/bladder pain syndrome: a systematic review

What this means for you

Persistent bladder pain, urgency or frequency without infection needs assessment by a urologist, since diagnosis is largely a matter of ruling other conditions out and several treatments can help with symptoms. In addition, the research above found the bacterial differences separating people with this condition from those without sitting in stool rather than urine, and the depleted species were butyrate producers. A varied, plant-rich diet supports the same gut bacteria this research ties to lower symptom severity. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.