My cat has chronic diarrhoea, negative stool tests and only partial improvement with hydrolysed food. Has anyone been through this?

[u/GlitterySeaweed]

My 3-year-old cat has been struggling with recurring soft stools and diarrhoea for months, and I’m starting to feel a bit lost. I’m hoping to hear from anyone whose cat has experienced something similar, especially if you eventually found something that helped.

Her symptoms:
- Chronic soft stools, sometimes progressing to watery diarrhoea.
- Very foul-smelling stools.
- During the worst episodes earlier this year, she strained and had some blood in her stool. She couldn’t relieve herself in the litter box so she did it on the carpets. This got better after the initial Giardia treatment.
- Otherwise, she seems well: she eats, plays, is affectionate, has a shiny coat and hasn’t lost weight.

What I’ve tried and tested:
- She received a short course of Metrobactin (metronidazole) earlier this year. Her stools became completely normal for a while, but the diarrhoea eventually returned.
- A faecal parasite test was negative.
- Giardia, coronavirus and parvovirus tests were negative.
- Her bloodwork was mostly within the reference ranges, although her folate was elevated.
- She has been eating Hill’s Prescription Diet z/d for several weeks. Her energy and general behaviour seem better, and her stools are sometimes more formed, but she still has episodes of diarrhoea. She may occasionally get into my other cats’ food, so the diet hasn’t been perfectly exclusive.
- She had a course of Proplan Fortiflora but I didn’t see any meaningful improvements.

My vet suspects IBS, but we haven’t established a definite cause yet. We’ve discussed seeing an internal medicine specialist, although I’m trying to work out which next steps might be most useful at this point.

For anyone who has dealt with something similar, did you eventually find a cause, even after negative stool tests?

I’d really appreciate hearing what helped in real cases. I am starting to feel the desperation and I cry sometimes because I cannot help her.

Thank you!