Wednesday, April 7, 2010

Endocrine Disease

Endocrine diseases are some of my least favorite topics. They can be confusing and complicated and hard for clients (and often veterinarians) to understand. Today I thought I would do an overview of some of the more common endocrine diseases in dogs in hopes that it might help someone better understand them, or what to be watching for in their own pet.

Hypothyroidism is an underactive thyroid gland and is the most common endocrine disorder of the dog. Fortunately it is also the simplest! The thyroid gland can be thought of as the metabolic control center of the body. So, in simple terms, everything slows down when the thyroid gland is not working enough (not producing enough thyroid hormone). The most common cause of this is idiopathic atrophy, meaning that the thyroid tissue is replaced by fatty tissue for unknown reasons, and lymphocytic thyroiditis, which is an inflammatory condition that allows the thyroid tissue to be replaced other kinds of cells. Neither of these conditions is a cancer or systemic disease. It is limited to the thyroid gland and all the effects are secondary to the lack of hormone production.

Common signs of hypothyroidism include lethargy, weight gain with a normal to decreased appetite, dull, dry coat including hair loss, seeking warm places to sleep, and decreased heart rate. There are other, less frequent signs, including seizures, which can occur if left untreated.

Diagnosis is made by simple blood testing. The most common test and usually the first one run is total T4 level. If this is low, then there will likely be some follow up testing to confirm the diagnosis. Usually this is active or unbound T4. Most thyroid hormone circulating is bound to a protein which makes it inactive. The total T4 tests the bound (inactive) hormone plus the unbound (active ) hormone. It's only the active we really care about. So the second test will give us that result and confirm the diagnosis. If your vet strongly suspects your dog is hypothyroid then they may run both tests at the same time, or some other thyroid panel, depending on their lab. The second test is relatively expensive, so the T4 is usually done first as a screening test.

Treatment for hypothyroidism is simple and involves giving your dog a small pill of synthetic thyroid hormone. This is usually given twice daily and is life long. There will be some follow up testing to make sure the dose is correct but once stable testing will only need to be done once or twice a year.

Diabetes Mellitus
Diabetes Mellitus is a lack of insulin production which subsequently decreases uptake of glucose from the blood stream into the cells. The initial cause of the decreased insulin production is not well understood but could include pancreatic disease, obesity, genetics, infection, immune-mediated, or rarely neoplasia.

Hallmark signs of diabetes are increased urination and thirst along with weight loss with a normal to increased appetite. Cataracts are another common finding. Left untreated, pets with diabetes can develop a severe condition known as diabetic ketoacidosis. Dogs with this advanced problem will often have decreased appetite, lethargy, and vomiting. These dogs typically require hospitalization and intensive care.

Diagnosis can be as simple as a blood glucose test and urinalysis (excess glucose spills into the urine). It is advisable, however, to have a more thorough blood testing done to screen for other concurrent or underlying problems. Abdominal radiographs or ultrasound are a good idea as well, although they are normal in most cases.

Treatment is aimed at controlling the clinical signs and regulating the blood glucose levels. This is typically done with a special diet and insulin administration. Usually the insulin is given twice daily (yes, you will have to give your dog an injection but the needle is very small!). Your veterinarian will likely have you do some monitoring at home and adjust the insulin dose based on these results. Usually this is with urine testing but some people purchase a glucose meter and do blood testing at home. Your vet will also likely do some blood glucose testing in the clinic, frequently at first, and then less as your pet become regulated and the correct dose of insulin is found.

Diabetic cataracts can be removed in most cases by an ophthalmologist. Dogs with diabetes are predisposed to urinary tract infections and doing a urinalysis or culture 1-2 times a year is frequently recommended.

Hyperadrenocorticism or Cushing's Disease
Cushing's disease is production of too much cortisol hormone by the adrenal gland. Most cases of Cushing's disease are caused by a benign tumor in the pituitary gland. The tumor causes an increase in an intermediate hormone that subsequently causes the adrenal gland to work overtime. A few dogs with Cushing's disease will have a tumor in the adrenal gland itself.

The most common signs are increased urination and thirst, increased appetite, a pot-bellied appearance, increased panting, hair loss, and muscle weakness.

Diagnosis can be complicated and expensive. Results of basic bloodwork and clinical signs can often give your vet a suspicion of Cushing's disease. The degree of suspicion often dictates which test will be run next. Frequently it takes multiple tests to finally arrive at the diagnosis.

There are currently several drugs that have been tried in the treatment of Cushing's disease. Unfortunately most (or all, I have not priced them all) are relatively expensive and some can have significant side effects if given inappropriately. Follow up tests (again, expensive) are then done to make sure dosing is at the desired level. Control of clinical signs is also a primary treatment goal. Some dogs have blood tests that indicate early Cushing's disease but no clinical signs. These dogs are usually just monitored and not treated until more abnormalities develop. Radiation therapy can be used in dogs with large pituitary tumors and removal of the adrenal gland is the recommended treatment for dogs with adrenal tumors.

Generally speaking these are all disease of middle-aged to older dogs. Hope this had been informative!


Border Collie Mom said...

Yikes! I think I have all of those! Do any of them also exhibit a desire to watch American Idol and eat ice cream?

(thanks, Nicki... all jokes aside I really enjoy your medical posts)

Sue said...

Good post. We're too familiar with two of the conditions.

tervnmal said...

Thanks for the explanations! Knowledge is a good thing. My first Sheltie developed Cushings at age 11. He responded well to meds and lived to age 16.

Elizabeth said...

How about some Addison's Education! Undiagnosed that is a killer.