Diabetes & Cushing’s: Frequently Asked Questions

Diabetes and Cushing’s disease are strongly linked and often occur together. Below are answers to frequently asked questions about these two conditions.

Can Cushing’s disease cause diabetes?

Yes, Cushing’s disease can cause some dogs to become diabetic. Diabates Mellitus is a condition that occurs when the pancreas doesn’t produce enough insulin or when the body doesn’t adequately respond to insulin, causing glucose to accumulate in the blood. Long-term overproduction of cortisol, as seen with Cushing’s disease, can bring about diabetes by increasing glucose levels in the bloodstream and causing cells to be less responsive to insulin.

About 10 percent of dogs with Cushing’s disease have concurrent diabetes.

What are the signs that a dog diagnosed with Cushing’s disease has also developed diabetes?

The clinical signs of diabetes are very similar to the signs of Cushing’s disease, so similar that it’s often challenging to distinguish one from the other. Symptoms to watch for are weight loss despite increased appetite, excessive thirst and urination, cloudy eyes, and lethargy or low energy. Veterinarians diagnose diabetes based on evaluation of clinical signs and laboratory findings. Glucose in the urine and persistently elevated blood sugar levels are strong indications that a dog is diabetic.

What are the signs that a dog diagnosed with diabetes has also developed Cushing’s disease?

In some cases, a veterinarian might suspect a diabetic dog of also having Cushing’s disease. This suspicion usually occurs when the dog’s diabetes is resistant to insulin therapy. According to Dr. Mark E. Peterson, a veterinary endocrinologist, a dog is insulin resistant when an insulin dose greater than 2.2 U/kg/injection is needed to control blood sugar. Other experts use a lower threshold of 1.5 U/kg.

Please note, insulin resistance does not necessarily mean that a dog with diabetes also has Cushing’s disease. Some dogs are simply more difficult to regulate and may need increasing doses of insulin before diabetes is controlled. Other reasons for insulin resistance could include improper insulin injection technique, outdated insulin, or incorrect syringes.

ACTH stimulation is the superior test for diagnosing Cushing’s disease in dogs with diabetes. The Low Dose Dexamethasone (LDDS) test is not recommended because it is likely to yield a false positive result in diabetic dogs.

Keep in mind, a Cushing’s test should not be conducted until the dog’s blood sugar is at least moderately controlled with insulin. Glycemic control is blood glucose 100-250 mg/dL (5.6-19.4 nmol/L). The veterinarian should conduct a blood glucose curve in conjunction with the ACTH test to ensure it is within this range.

What’s the best treatment approach for dogs with diabetes and Cushing’s?

Treatment for dogs with diabetes and concurrent Cushing’s needs to be carefully managed. If a diabetic dog is taking Vetoryl (trilostane) for Cushing’s disease, the total daily dose should be split into two and be given every 12 hours. Since Vetoryl (trilostane) is a short-acting drug, twice a day dosing allows for more continuous control of cortisol.

Lowering cortisol levels can lessen insulin resistance and result in more profound glucose lowering activity by the usual insulin dose. Some experts recommend reducing a dog’s current insulin dose by 25 percent upon initiation of Cushing’s treatment. However, this may not be required in all cases.

To monitor a diabetic dog being treated for Cushing’s, owners will normally be sent home with urine test strips and instructed to measure urine at least once per day approximately 6 hours after insulin is given (if given twice per day). If ketones are detected or the absence of urine glucose is detected more than twice in a row, the owner should inform the veterinarian. Lack of urine glucose may indicate hypoglycemia, requiring immediate care.

Will treating Cushing’s cure diabetes?

Reducing cortisol levels, through Cushing’s treatment, can significantly lessen insulin resistance and improve diabetes. However, it’s unlikely to completely cure diabetes for most dogs.

References

Q&A: Diagnosing Cushing’s Disease is Dogs with Diabetes Mellitus, by Dr. Mark E. Peterson

A Big Picture Look at Cushing’s and Diabetes, by Dr. Joi Sutton

The Double Challenge of the Diabetic Cushingoid, by Cynthia R. Ward

Diabetes in Dogs, by Cornell Canine Health Center

Methodologies for Dealing with Concurrent DM and HAC issues, by Gerard McLauchlan and Ian Ramsey

Cushing’s and Diabetes Mellitus, by Glynda Pomerantz and Darrell Bailey