Diabetes in Cats, Part I

March 29, 2019

One of the common illnesses we see in cats is Diabetes Mellitus (DM). Because it is common in people, most people at least know that DM causes high blood glucose (sugar). This is complicated issue, so we’ll split it up into two parts. Today, we’ll talk about what diabetes is, the types of diabetes, symptoms, and diagnosis.

Let’s start at the beginning and talk about how sugar is normally supposed to act in the body. The cells of the body need fuel for their day to day functions, glucose and/or fat (some tissues can use both and others like the brain can only use glucose). Insulin is a hormone produced by the pancreas that allows glucose to move from the bloodstream into cells. One way to think about it is that insulin acts like a key to open doors that allow glucose to enter rooms (cells) from a hallway (bloodstream). Without insulin, the doors stay locked and glucose can’t leave the hallway or get into the rooms.

DM occurs when there is not enough insulin in the body to move glucose into all the cells. We don’t always know what causes DM in every cat. There is likely a genetic component, and we do know that obesity is one of the biggest risk factors for DM in cats. It can also occur secondary to some hormonal disorders.

The classic symptoms of DM in cats are: increased thirst, urinating large volumes of urine, increased appetite, and weight loss. But why do we see these signs?

Normally, the kidneys keep glucose in the bloodstream rather than passing it in the urine. However, in DM the glucose builds up to such a high level that it overwhelms the kidneys and spills into the urine. Because glucose attracts water, it drags a large amount of water along with it. This results in a large volume of dilute urine. These cats then have to drink more water to make up for what is lost in the urine. At the same time, the body’s cells are starving. In response, the body starts to break down its fat and muscle cells for energy and the appetite is stimulated.

We do not classify cats as type I or type II diabetics as in humans, but into insulin dependent DM (IDDM) or non insulin-dependent DM (NIDDM). Most diabetic cats (~75%) have NIDDM; their pancreas is making some insulin, just not enough.  The name is misleading because we do need to start treating these cats with insulin when they are diagnosed. It has this name because some cats with NIDDM can achieve diabetic remission. This means their pancreas can start producing normal amounts of insulin again. Long term, cats in remission can stop getting insulin injections and can usually be maintained with diet (although some may relapse).

About 25% of cats have IDDM, and their DM is almost always secondary to other hormonal diseases. Acromegaly (hypersomatotropism) is the most common. Acromegaly is caused by a tumor on the pituitary gland in the brain secreting excessive amounts of growth hormone; this has many effects on the body, including IDDM. These cats are managed just like cats with NIDDM with diet and insulin, but often require very high doses of insulin and may be difficult if not impossible to regulate perfectly. We often recommend additional testing for acromegaly in a diabetic cat who is difficult to regulate or needs unusually high doses of insulin.

Solo, Dr. Christopherson’s cat, has IDDM secondary to acromegaly.

Diagnosis of diabetes is made with history (increased thirst, urination, and hunger with weight loss) and laboratory tests (high blood glucose*, glucose in the urine). Because several chronic diseases share these clinical signs, we recommend a comprehensive panel of tests in these cats instead of just testing blood glucose. In newly diagnosed diabetic cat, we recommend the addition of a test called fructosamine. Fructosamine gives us a picture of what the glucose has been over a longer period of time vs at the instant in time a blood glucose measurement is taken (slightly similar to A1c in people although not exactly the same).  We often use this in monitoring diabetic patients and having a baseline before treatment is started is very valuable.

(*Note: It is very normal for stress to cause a temporary, relatively minor spike in blood glucose, but this should not be mistaken for DM which causes extreme elevations in blood sugar that is many times normal.)

That’s enough information for today! Next week, we’ll cover treatment options, monitoring, and expectations for diabetic cats, along with some reputable online resources.

Karen Christopherson DVM CVA