In dogs and cats, diabetes mellitus is subdivided into three different types– I, II and III.
Type I diabetes occurs most commonly in dogs. The islet cells in these animals are destroyed and cannot produce insulin. Treatment to control blood glucose levels in these patients require insulin injections just as do people with insulin-dependent diabetes mellitus.
Type II diabetes is more common in cats and is similar to non-insulin dependent diabetes in humans. Patients with this condition suffer from insulin resistance as well as problems secreting insulin. Obesity is thought to be a trigger for this type of diabetes. Although it is possible to control some cats with diet and oral hypoglycemics, others require insulin injections.
Type III diabetes is characterized by something within the patient that interferes with insulin and leads to glucose intolerance. In my experience, Cushings’ Disease (Hyperadrenocorticism) is the most common cause of type III diabetes. It may also occur secondary to glucocorticoid (prednisolone or prednisone) therapy. Sometimes, this type of diabetes will often resolve after the drug is withdrawn or the Cushings’ disease is treated.