Autoimmunity is closely connected to the
health of the digestive
tract; it's been linked to increased intestinal permeability (often referred to as «leaky gut»), so it's no surprise that healing from interstitial cystitis
starts with diet.
If your cat normally has no problem with using the litter box and suddenly
starts using your carpet as a toilet there could be a
health issue, a urinary
tract infection or cat diabetes, or feline kidney disease.