About: Colitis is an inflammation of the colon (large intestine) which is the last part of the digestive tract in cats. Water is absorbed in the colon and feces are stored until the cat passes it out of the body.
Causes: There are a number of causes of colitis in cats which include infection, food allergy or intolerance, parasites, pancreatitis, cancer, dietary indiscretion, and stress.
Symptoms: Frequent watery stools which may contain blood or mucus, loss of appetite, vomiting, dehydration, lethargy, abdominal pain.
Diagnosis: Complete physical examination and baseline tests including complete blood count, biochemical profile and urinalysis. Fecal tests to look for parasites, colonoscopy, and biopsy, and possibly additional tests depending on your veterinarian’s index of suspicion.
Treatment: Find and treat the cause, as well as a low-fat diet, anti-inflammatory medications and supportive care where necessary.
What is colitis?
Colitis is the inflammation of the lining of the colon (large intestine). It may be chronic, symptoms have been present for 14 to 21 days, or acute (sudden onset).
The colon is responsible for extracting water from the feces and storing fecal matter prior to evacuation (bowel movement).
Inflammatory bowel diseases are classified according to the type of inflammatory cell infiltrating the gastrointestinal wall. Lymphocytic-plasmacytic enterocolitis is the most common form of IBD. Lymphocytes (a type of white blood cell) and plasma cells (antibody producing cells) are the predominant types of inflammatory cells present in the mucosa of the small and large intestine. Eosinophilic Enterocolitis is the second most common form of IBD, eosinophils may be found in the stomach, small intestine or colon, Granulomatous (Regional) Enteritis in which macrophages are found in the lower small intestine and colon.
If the inflammation is restricted to the large intestine it is referred to as colitis, if the small intestine is involved it is referred to as enteritis and if both the large and small intestine are involved it is referred to enterocolitis, if the stomach is involved it is referred to as gastritis. 
There are several causes of colitis including:
Certain bacteria (Salmonella and Campylobacter), viruses and fungi.
Stress – Moving house, a new family member, change in routine etc.
The most obvious sign of colitis is diarrhea, possibly outside the litter tray because of the ‘urgency’ to go. The stool is often soft or watery and may contain blood or mucus. Other symptoms may include;
Straining in the litter tray causing discomfort.
Diarrhea (the stool may start out normal but finish off loose or watery)
Your veterinarian will perform a physical examination of your cat and obtain a medical history, including symptoms you have noticed. Your veterinarian may be able to determine a cause depending on how the colitis has presented. Was it acute (sudden onset), chronic (lasting several weeks) or episodic (comes and goes)?
Fecal test for bacteria, nematodes (worms) and Giardia.
Complete blood count. Most cases will reveal a normal CBC but some cats may have become anemic. Higher numbers of white blood cells may be observed.
Chemistry profile (biochemistry profile) to evaluate for diabetes mellitus, liver disease, renal disease.
X-Rays/ultrasound don’t help diagnose colitis but are useful to rule out other medical conditions such as cancer.
Colonoscopy and biopsy to determine the type if inflammatory cell present, check for cancer.
Feline trypsin-like immunoreactivity (fTLI) to evaluate for pancreatitis.
FIV and FeLV tests may suggest if a secondary disease is present.
Total T4 (TT4) to evaluate for hyperthyroidism as diarrhea can be a symptom.
The goal of treatment is to identify and eliminate the cause as well as give supportive care. This may include:
Provide a high fibre diet if the colon is affected.
Anti-inflammatory medications to reduce inflammation.
Supportive care such as fluids to treat dehydration and nutritional support.