My cat eats constantly, loses weight, has diarrhea, tests negative. Why?

These are indeed an unusual set of symptoms, thyroid disease and diabetes would be the first suspects for a cat with increasing appetite and weight loss. A specialist ultrasound scan of the abdomen may be worth while to investigate difficulties with food digestion and absorption or even tumours using up the calories

It sounds as though you and Schumacher have been through a lot over the past 2 years! Given his weight loss, chronic diarrhea, normal blood work and initial response to depomedrol, chronic pancreatitis or primary intestinal issues, such as inflammatory bowel disease or lymphoma would be my main concerns. In this situation, further diagnostic testing is often needed to try to get to the bottom of this issue. Some tests include vitamin absorption and pancreatic blood tests (B12, folate, TLI, fPL) and an abdominal ultrasound to look at his internal organs, intestinal thickness, lymph nodes, etc. In some cases, biopsies are needed to differentiate between different conditions so that the most appropriate treatment can be started. Cats with inflammatory bowel disease or lymphoma often benefit from long-term steroids, antibiotics and prescription diets to control their clinical signs. I hope that all goes well for Schumacher!

The thyroid level can change in a month, especially if Dewey’s previous thyroid level was towards the middle of the normal range. There are also some other more specific tests that can be positive before the total thyroid hormone level increases. A few other diseases that can cause weight loss with a normal appetite include intestinal parasites, diabetes or occasionally certain types of cancer. If Dewey is continuing to lose weight I would recommend rechecking with your vet.

It is fairly rare, but ask your veterinarian if your kitty may be suffering from Cushing's disease or liver disease. Also sometimes cats can still be hyperthyroid, even though the thyroid parameters are within normal limits (this is called euthyroid sick). He could also have a tumor. In any case, this needs to be investigated further.

I definitely think you should have Dahlia examined by your veterinarian. A few diseases that could cause an increased appetite with weight loss include intestinal parasites, diabetes, and hyperthyroidism. Your vet can examine Dahlia and her stool, and may recommend checking lab work if parasites seem unlikely. All of these diseases are very treatable, but it's important to get a diagnosis quickly.

Poor Sachi! Significant weight loss and inappetence are certainly a major concern. I'm glad to hear that his blood work (I assume a CBC, chemistry and T4?) was unremarkable. However, foreign body intestinal obstruction/blockages, intestinal malabsorption issues that can cause inflammatory bowel disease (IBD) or exocrine pancreatic insufficiency (EPI), chronic pancreatitis, or cancerous processes, do not necessarily cause changes on screening blood tests. If Sachi has not yet had abdominal x-rays or an ultrasound, consider talking to your vet about these tests as his next diagnostic step. If he has a foreign body obstructing his intestines, this is a surgical emergency, and these tests would be helpful in obtaining a diagnosis. If pancreatitis, IBD or EPI are more highly suspected, consider talking to your vet about testing for vitamins B12 and folate, as well as TLI and fPLI. I hope this helps!

Food allergies could be one of the reason for the persistent diarrhoea and weight loss, but these conditions must be differentiated from IBD (inflammatory bowel diseases) and unfortunately from more sinister conditions like tumors. Weight loss in old cats can have different causes as well, and endocrine diseases (hyperthyroidism and diabetes mellitus) are frequently associated with intestinal diseases as well. Considering all these possible clinical scenarios, I would recommend a check up and more tests (blood test+urine analysis including thyroid hormone and feline pancreatic lipase and possibly an ultrasound of the abdomen) to determine underlying cause and treat appropriately. Please do not hesitate to contact us again on the forum or by requesting a consultation if you have any more questions or to discuss it any further.