Weekly Cat Vomiting: IBD, Hairballs and Low-Grade Lymphoma

Vomiting once or twice a week is not "just a sensitive stomach." In a cat, that frequency is a symptom worth investigating, and the hairball that owners blame is usually the visible end of a motility problem rather than a normal event. The practical threshold is simple: more than 2 vomits a month, or any vomiting that comes with weight loss, means a workup. Chronic enteropathy, meaning inflammatory bowel disease (IBD) or low-grade lymphoma, is the most common finding, and the two are hard to separate even on biopsy.

What counts as abnormal, and why owners underestimate it

Cats vomit quietly, often at night, and the mess is easy to normalize. Ask three questions instead. How often: once a month may be tolerable in a cat that is gaining weight and eating normally, once a week is not. What comes up: digested food means the stomach had time to work, undigested food within an hour of eating points to a motility or gastric problem, foam or yellow fluid means an empty stomach, and hair with bile is not "normal grooming." What else changed: weight, appetite, stool volume, and whether the cat now eats in small bursts and walks away.

A cat that lost 10 percent of body weight over 6 months while vomiting weekly has a real disease, and 10 percent is often only 400 to 500 grams, hidden under a winter coat.

Why hairballs usually mean a problem, not a habit

Cats swallow hair every day, and healthy cats pass it in stool. A hairball is a felt-like mass that has been sitting in the stomach long enough to mat, which means transit was already slow. In practice, most cats that bring up hairballs more than about once every 2 weeks have an underlying chronic enteropathy, and removing the hair with a laxative treats the sign while the inflammation continues. Two exceptions exist: a long-haired cat in heavy shed, and over-grooming driven by itch or stress. Even then, rule out the gut first.

The minimum workup, in the order most clinics run it

Test	What it rules out	Why it comes first
CBC and chemistry panel	Anemia, dehydration, liver and kidney values	Cheap, fast, sets the baseline for steroids
Total T4	Hyperthyroidism	Very common in cats over 8 and causes vomiting
Feline pancreatic lipase (fPL)	Pancreatitis	Often coexists with IBD
Cobalamin and folate	Small intestinal bacterial overgrowth, ileal disease	Low B12 predicts where the disease sits
Abdominal ultrasound	Mass, intussusception, thickened bowel, gall bladder disease	Guides whether to biopsy
Fecal panel and deworming	Parasites, Giardia, Tritrichomonas	Cheap and treatable

Skip no step because the cat "seems fine." Young cats with chronic vomiting are more likely to have parasites or a dietary intolerance; cats over 8 are more likely to have hyperthyroidism, lymphoma or triaditis. Age changes the prior probability, not the list.

Ultrasound tells you where, biopsy tells you what

Ultrasound shows bowel wall layering thickness, usually reported in millimeters, and normal small intestine is under about 3 mm. It can also show a muscularis layer that is disproportionately thick, loss of layering, or an enlarged mesenteric lymph node. What it cannot do is distinguish inflammation from neoplasia. Full-thickness surgical biopsy with histopathology is the gold standard; endoscopic biopsy is less invasive but only reaches the stomach and duodenum, so it misses disease in the jejunum and ileum. If the cat is stable, most internists still start with a diet trial and reserve biopsy for failure to respond or for a focal mass.

IBD and low-grade lymphoma look the same under the microscope

Both produce a lymphocytic infiltrate in the lamina propria, and pathologists disagree on where inflammation ends and neoplasia begins. Two add-ons help. Immunohistochemistry stains for CD3 and CD79a to characterize the population, and PARR testing looks for clonal antigen receptor rearrangement, which supports lymphoma. Neither is perfect: a clonal result strongly supports lymphoma, while a polyclonal result does not fully exclude it. Clinical behavior often decides: a cat that responds within 4 to 6 weeks of steroids and holds the response for a year is behaving like IBD, while a cat that improves and relapses repeatedly, or has a palpable mass, behaves like lymphoma.

The diet trial has to be strict or it proves nothing

Two options work. A hydrolyzed protein diet breaks the protein into fragments too small to trigger an immune response. A single novel protein diet uses a protein the cat has never eaten, such as venison, rabbit or insect-based food, introduced by gradual transition. Either way the trial runs 4 to 8 weeks, and during that window the cat gets nothing else: no treats, no table food, no flavored liquid medication, no other cat's bowl. A cat that raids the dog's dish has not had a trial. Owners who cannot enforce this should say so at the start, because a trial on a contaminated diet leads straight to biopsy.

B12 is not optional

Cobalamin is absorbed in the ileum, so chronic small intestinal disease lowers it, and low B12 impairs the lining's ability to recover. Most clinicians supplement when the level is low, typically cyanocobalamin injected under the skin weekly for 6 weeks and then monthly, with a recheck at 3 months. It is cheap, and correcting it improves appetite and weight independent of the steroid dose.

Steroids: starting dose, taper, and what to watch

Prednisolone is started at roughly 1 to 2 mg per kilogram per day for 2 to 3 weeks, then tapered over 6 to 12 weeks to the lowest dose that holds remission, ideally every other day. Budesonide is an alternative with more first-pass liver metabolism and fewer systemic effects, dosed around 1 mg per cat per day. Before starting, confirm there is no active infection and no diabetes, because steroids raise blood glucose. Recheck weight, appetite and B12 at 4 to 6 weeks; a cat that has not improved by then needs the biopsy, not a higher dose. Never stop prednisolone abruptly after months of use.

Signs that mean today, not next week

1. Vomiting more than 3 times in 24 hours, or vomiting after every meal.
2. Weight loss above 10 percent, or ribs and spine becoming visible.
3. Blood in the vomit, black tarry stool, or yellow gums and skin.
4. Refusing food for 24 hours in an adult, 12 hours in a kitten.
5. A tense, painful abdomen, or a cat that sits hunched and will not lie down.

Chronic vomiting is one of the few feline problems where early workup changes the outcome: the gap between inflammation and lymphoma is measured in months of good appetite. A log of vomit dates, weight and stool quality tells the vet more than any single test.

Frequently asked