6: Endocrine System

SECTION 6 Endocrine System



Section Editor: Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO



Diabetes Insipidus

Diabetes Mellitus in Cats

Diabetes Mellitus in Dogs

Hyperadrenocorticism (Cushing’s Disease) in Dogs

Hypercalcemia

Hyperlipidemia

Hyperthyroidism in Cats

Hypoadrenocorticism (Addison’s Disease)

Hypoglycemia

Hypothyroidism in Dogs


Diabetes Insipidus


Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO



BASIC INFORMATION



Description


Diabetes insipidus (DI) is also called water diabetes, because it is characterized by excessive drinking and urination. It is a separate disease from sugar diabetes. There are two major forms of diabetes insipidus, and both conditions are uncommon:


• Central DI arises from decreased output of vasopressin (antidiuretic hormone) in the brain. Vasopressin acts on the kidneys to increase the concentration of the urine (that is, to decrease its water content).

• Nephrogenic DI arises when the kidneys do not respond to vasopressin hormone.


Causes


Central DI may occur as a congenital defect (rare and present at birth) or may arise following infections, inflammation, trauma, or tumors of the brain.


Nephrogenic DI may also rarely occur as a congenital defect. More often, the nephrogenic form develops after an infection of the kidneys or uterus or as a consequence of chronic renal failure. It may also develop with certain metabolic problems, such as high calcium and low potassium levels, hyperadrenocorticism (too much circulating cortisone hormone in the body), and hyperthyroidism (high thyroid hormone levels). Certain drugs may also cause nephrogenic DI.



image Clinical Signs


The main signs of DI are dramatic thirst and the passage of very dilute (watery, light-colored) urine. Thirst can be so severe that the animal may seek out water from unusual places, such as toilets or ponds. Increased frequency of urination is usually noted. Urinary accidents in the house are common in dogs that do not have ready access to the out-of-doors. Weight loss, decreased appetite, and neurologic signs are sometimes seen.



image Diagnostic Tests



• Urine is very dilute or watery and almost clear in color.

• Other routine laboratory tests are often normal in cases of central DI. Kidney tests, urine cultures, and other tests may be abnormal in cases of nephrogenic DI. It is often necessary for a number of laboratory tests to be run to search for the cause of DI and to rule out other causes of increased thirst and urination.

• Specific tests that may be used to diagnose (confirm the presence of) the disease include a water deprivation test and administration of manufactured vasopressin.

• The water deprivation test involves careful withdrawal of water to determine whether the urine becomes concentrated. There are several techniques for performing this test; some require hospitalization, and all must be done with careful monitoring for dehydration and kidney problems.

• The vasopressin test involves giving the hormone and then monitoring the kidneys’ response to it. There are also several ways to perform this test.


TREATMENT AND FOLLOW-UP




image Treatment Options


Treatment of central DI involves giving vasopressin hormone. The hormone is currently available as eye drops and in pill form; nasal drops have been available in the past. The hormone is expensive and often must be given twice daily.


Nephrogenic DI is difficult to treat because there are no direct remedies available. Certain diuretics sometime help the symptoms of nephrogenic DI.


With both conditions, the animal must be allowed unlimited access to water, or severe dehydration and kidney failure may occur.



image Follow-up Care


Close monitoring of water consumption and urine concentration are required while medication dosages are being adjusted.



Prognosis


The prognosis is variable, depending on the underlying cause and form of the disease. If the response to vasopressin is good, then it can be used long term. The disease is usually irreversible.



SPECIAL INSTRUCTIONS:



Diabetes Mellitus in Cats


Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO



BASIC INFORMATION



Description


Diabetes mellitus (DM) is also known as sugar diabetes. The word mellitus means “sweet” and refers to the increased blood and urine sugar levels that occur with this disease. DM arises when the pancreas gland does not produce enough insulin. Insulin is the hormone that allows many tissues of the body to utilize blood sugar (glucose). As insulin levels falls, blood sugar becomes elevated, producing many adverse side effects in the body.



Causes


The most common cause of DM in the cat is the destruction of beta cells in the pancreas. Beta cells are responsible for insulin production. This destruction often arises from chronic inflammation of the pancreas gland. This type of diabetes is known as type I DM.


Type II DM, which arises either from the development of resistance to insulin or from a decreased action of insulin within the body, is uncommon in cats.



image Clinical Signs



• DM affects many different breeds and types of cats. The disease is most often seen in neutered male cats, 10 years of age or older.

• Common clinical signs include increased thirst and urination, increased appetite, and weight loss. Because glucose cannot be utilized by the body, it is almost as if the cat is starving in the midst of plenty.

• Some cats are also lethargic and weak and may walk with the hocks (ankles) of their hindlegs dropped to the floor.


image Diagnostic Tests


DM is diagnosed when the fasting blood sugar concentration is significantly elevated. Cats that are stressed have the ability to temporarily raise their blood sugar to levels above normal, so repeated blood glucose tests and the testing of urine for the presence of glucose may be needed to confirm the disease.


Additional tests are often indicated to look for other diseases (such as urinary tract infection or fatty infiltration of the liver) that may accompany DM. Such tests include a complete blood count, biochemistry profile, urinalysis, urine culture, abdominal x-rays, etc.


Because older cats are also prone to hyperthyroidism (elevated production of thyroid hormone), thyroid tests may also be submitted.



TREATMENT AND FOLLOW-UP




image Treatment Options


Cats with type II DM or very mild type I DM may respond to an oral medication (glipizide) that lowers blood sugar.


Most cats, however, require injections of insulin to control their disease. Several forms of insulin are available, and each has a different duration of action:


• Protamine zinc insulin (PZI) is preferred in many cats because it can often be given just once daily. It is not always readily available, however. Other types of insulin that may be tried in the cat are Ultralente and NPH insulin.

• Glargine (Lantus) is a new sustained-release insulin that has been tried in small numbers of cats, using a once- or twice-daily dosing schedule. Until more cats are treated with this insulin, initial dosing can be tricky.

• Vanadium, an oral supplement, is occasionally given to cats that require large doses of insulin, in an attempt to lower the amount of insulin they need each day.

In addition to insulin, the diet may be changed to a low-fat, high-fiber type of diet that contains complex carbohydrates. Several such foods are available by prescription through your veterinarian. Although it is difficult to train cats to eat meals, it is best if they eat around the time the insulin injection is given.



image Follow-up Care


Diabetic cats can be difficult to monitor at home because collection of their urine can be tricky, they often eat throughout the day rather than eating their meals all at one time, and they become stressed and may not eat when hospitalized.


Most monitoring is done by checking the level of glucose in small blood samples. Samples may be taken by your veterinarian at specific times during the day or throughout the day, over a prolonged period.


Monitoring may also be done at home in some instances, through pinprick sampling and testing of those samples on glucometers designed for use in diabetic people.


It is important to work closely with your veterinarian to establish a method for monitoring blood sugar and/or urine sugar while the cat is on insulin therapy.



Prognosis


The prognosis for many cats with DM is good, as long as the disease can be regulated and other ancillary problems can be controlled or resolved.


Successful treatment of this disease requires that the owner learn to give injections, become familiar with the signs of insulin overdosage and underdosage, and learn how to adjust insulin dosages.


With dedication on the part of the owner, many diabetic cats live active, normal lives for many years.



SPECIAL INSTRUCTIONS:



Diabetes Mellitus in Dogs


Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO



BASIC INFORMATION



Description


Diabetes mellitus (DM) is also known as sugar diabetes because of the increased blood and urine sugar levels that occur with this disease. DM arises when the pancreas gland does not produce enough insulin. Insulin is the hormone that allows many tissues of the body to utilize blood sugar (glucose). As insulin levels falls, blood sugar becomes elevated, producing many adverse side effects in the body.



Causes


The most common cause of DM in the dog is the destruction of beta cells in the pancreas. Beta cells are responsible for insulin production. This destruction often arises from chronic inflammation of the pancreas gland. This type of diabetes is known as type I DM.


In the keeshond breed, type I DM is an autosomal recessive trait in which one abnormal gene is inherited from each parent.


Type II DM, which arises either from the development of resistance to insulin or from a decreased action of insulin within the body, is rare in dogs.



image Clinical Signs



• The miniature schnauzer, miniature poodle, toy poodle, Samoyed, and pug are at increased risk. The usual age at onset is 7-9 years. Females develop DM more often than males.

• Common clinical signs include increased thirst and urination, increased appetite, and weight loss. Because glucose cannot be utilized by the body, weight loss occurs even with more food intake.

• Some dogs may develop cataracts very suddenly and go blind.

• A severe form of complicated DM called diabetic ketoacidosis may cause the animal to become terribly ill, with vomiting, depression, weakness, dehydration, and rapid breathing.


image Diagnostic Tests


DM is diagnosed when the fasting blood sugar concentration is significantly elevated. A urinalysis may also show sugar (glucose) and ketones in the urine.


Additional tests are often indicated to look for other diseases (such as urinary tract infection or inflammation of the pancreas) that may accompany DM. Such tests include a complete blood count, biochemistry profile, urinalysis, urine culture, abdominal x-rays, etc. If Cushing’s disease (overactivity of the adrenal glands) is also suspected, hormonal tests may be performed.



TREATMENT AND FOLLOW-UP




image Treatment Options


Most dogs with DM require injectable insulin to control their disease. Insulin comes in three forms: short-acting (regular insulin—Humulin R, Novolin R), intermediate-acting (NPH or PZI—Humulin N, Novolin N, Vetsulin, Caninsulin, PZI Vet), and long-acting (glargine—Lantus). Regular insulin is used most often for diabetic ketoacidosis. Twice-daily injections are needed by most dogs, even when the longer-acting insulins are given.


In addition to insulin, the diet may be changed to a low-fat, high-fiber type of food that contains complex carbohydrates. Several such foods are available by prescription through your veterinarian. Exercise and activity levels are often regulated so that they do not fluctuate widely from day to day.


Dogs with diabetes ketoacidosis usually require hospitalization with administration of intravenous fluids, multiple injections of regular insulin, and frequent monitoring of blood sugar.


Because other hormones effect DM, intact female dogs should be spayed, and other hormonal abnormalities (Cushing’s disease, hypothyroidism) should be corrected. Dogs with cataracts must have their DM well regulated prior to surgery.



image Follow-up Care


Monitoring is extremely important to keep the blood sugar within the desired range. Too much insulin or too little food intake (poor appetite, vomiting) may result in hypoglycemia (low blood sugar). Too little insulin results in persistently high blood sugar that may lead to ketoacidosis.


Home monitoring often involves keeping track of water intake and the frequency of urinations, checking urine for sugar and ketones, using a glucometer and pricking the skin or the ear to measure blood sugar, and monitoring appetite and food intake.


In-clinic monitoring involves checking blood sugar, possibly as a glucose curve. A glucose curve is produced by measuring blood sugar several times over the course of the day, after insulin is administered and the dog is fed as usual. Other laboratory tests may be repeated to ensure that the complications of DM are resolving.


Sometimes glucose curves can be obtained at home with the use of a glucometer or a continuous, subcutaneous device.


Based on test results, the dose of insulin is adjusted. It is increased when blood sugar is high and decreased when blood sugar is low.



Prognosis


DM can be challenging to regulate and may require patience and persistence, but it can be successfully managed in most dogs. It is necessary for owners to educate themselves about the disease and to remain in close contact with their veterinarian. Most dogs readily accept the injections and the necessary monitoring.



SPECIAL INSTRUCTIONS:



Hyperadrenocorticism (Cushing’s Disease) in Dogs


Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO



BASIC INFORMATION



Description


Hyperadrenocorticism arises from overproduction of glucocorticoid hormones by one or both adrenal glands (Cushing’s disease) or from chronic or excessive administration of steroid medications (Cushing’s syndrome). In atypical cases, other adrenal hormones, such as sex hormones, may also be elevated.



Causes


Pituitary-dependent hyperadrenocorticism (PDH) develops when a tumor of the pituitary gland produces high levels of adrenocorticotropic hormone (ACTH), which subsequently causes the adrenal glands to become overactive. PDH is the most common cause (85%) of Cushing’s disease in the dog. Most pituitary tumors are small (microadenoma) and do not cause neurologic signs, but large tumors (macroadenoma) occur in about 30% of affected dogs. Since ACTH influences both adrenal glands, both glands are usually enlarged with this form of the disease.


Adrenal tumors occur in 15% of affected dogs, and about half of these tumors are malignant. Often, only one adrenal gland is affected and enlarged.


Iatrogenic hyperadrenocorticism arises from prolonged or excessive administration of glucocorticoid medications (such as prednisone, dexamethasone, hydrocortisone, triamcinolone, or methylprednisone). Since the pituitary gland constantly detects high levels of steroids in the blood, it decreases the production of ACTH, which causes both adrenal glands to shrink.



image Clinical Signs


Most affected dogs are middle-aged or older. The miniature poodle, dachshund, boxer, Boston terrier, and beagle are predisposed to the disease. Adrenal tumors occur more often in female, large-breed dogs.


Common clinical signs include the following:


• Increased thirst, urination, appetite

Related posts:

  1. 16: Behavioral Disorders
  2. 8: Reproductive System
  3. 2: Cardiovascular System
  4. 15: Infectious Diseases

Stay updated, free articles. Join our Telegram channel
Tags:
Sep 11, 2016 | Posted by in SMALL ANIMAL | Comments Off on 6: Endocrine System

Full access? Get Clinical Tree
Get Clinical Tree app for offline access