List of Dog Diseases - Endocrine Diseases

Endocrine Diseases

• Diabetes mellitus in dogs is type 1, or insulin dependent diabetes: a lack of insulin production due to destruction of pancreatic beta cells. Current research indicates no evidence of type 2 diabetes in dogs. Among the causes of diabetes mellitus in dogs are autoimmune disease or severe pancreatitis. Forms of diabetes which may not be permanent, depending on the amount of damage to the beta cells of the endocrine pancreas, are transient and secondary diabetes. Some causes of transient or secondary diabetes are Cushing's syndrome, glucocorticoid, progestin or other steroid use, and the hormones of pregnancy or heat. In these cases, correcting the primary medical issue may mean a return to non-diabetic status. Common signs include weight loss, increased drinking and urination, and cataracts. Treatment involves twice daily insulin doses (replacement therapy) and use of a diet high in fiber and complex carbohydrates. Oral diabetes medications are not able to be used for dogs because none are capable of repairing or surmounting the permanent damage to the beta cells of the pancreas.

• Thyroid diseases, including:
  • Hyperthyroidism* is rare in dogs. The most common cause is thyroid carcinoma, a malignant tumor. Signs include weight loss, increased appetite, and enlargement of the thyroid gland.
  • Hypothyroidism is the most common endocrine disease in dogs. It can be caused by autoimmune destruction (lymphocytic thyroiditis) or idiopathic atrophy of the thyroid gland. These two causes are responsible for over 95% of the hypothyroidism cases in dogs. Signs include decreased appetite, weight gain, hair loss, dry skin/coat, skin that is cold to the touch, recurring skin infections, and lethargy. The dog may also seek out warm places to lie. The symptoms of hypothyroidism are shared with many other medical conditions; it may not be the first thought when a diagnosis is made. Symptoms may not appear until 75% or more of the gland is non-functional. In less than 10% of hypothyroidism cases, the problem is not with the thyroid gland itself, but with the pituitary gland in the brain. The pituitary gland produces a thyroid stimulating hormone (TSH); without this hormone to signal the thyroid gland to produce its thyroid hormone, the thyroid gland remains inactive. Treatment is with oral thyroid hormone supplementation. Lack of enough iodine in the diet can produce a form of hypothyroidism; without the proper amount of it, the thyroid gland fails to produce enough thyroid hormone. Myxedema coma is a rare but serious aspect of the disease that is a medical emergency.
• Addison's disease, also known as hypoadrenocorticism, is a reduction of production of glucocorticoids and mineralocorticoids by the adrenal glands. There is more familiarity with the glucocortcoids, such as cortisol; mineralcorticoids control the amount of potassium, salt and water in the body. It is most commonly caused by destruction of adrenal tissue, probably by autoimmune disease. Signs include increased drinking and urination, vomiting, diarrhea, collapse, shivering and weight loss; at times neither the causes nor symptoms are especially specific. Because of this it is sometimes referred to as "the Great Mimic" or "the Great Imitator". It is possible not to see any symptoms of the disease until the adrenal cortex is 90% dysfunctional. Addison's can occur when regular steroid use is abruptly discontinued; during their use, the system the adrenal gland does not function at 100%. The system senses sufficient levels of these hormones in the body and does not signal for their production. Tapering the medication off gradually allows them to return to full production after discontinuation. About 35% of canine Addison's patients are not diagnosed until they experience an Addisonian crisis, which outwardly appears to be a "classic" shock and is a medical emergency. Hyperkalemia can develop and cause severe bradycardia. Only typical Addison's patients have the risk of Addisonian crisis due to the lack of mineralocorticoids. Treatment is with supplementation of mineralocorticoids in daily pills or a monthly injection. The atypical form and the form caused by abrupt withdrawal of steroids do not need mineralocorticoids. Glucocorticoids are usually supplemented with oral prednisone.

• Cushing's syndrome, also known as hyperadrenocorticism, is a condition characterized by an increase in glucocorticoids secreted by the adrenal glands. About 85 percent of cases are caused by a tumor in the pituitary gland, while 15 percent are caused by an adrenal tumor. The pituitary gland produces a hormone that signals the adrenal gland to produce cortisol; a tumor can cause it to produce the adrenal-stimulating hormone even when it is not needed. Signs include increased appetite, increased drinking and urination, a pot-bellied appearance, muscle weakness, and lethargy. Cushing's can be caused by overuse of steroid medications; in some cases, stopping the medication is enough to solve the problem. Diagnosis can be difficult as there are no tests with both high sensitivity and specificity. Treatments inclulde mitotane, trilostane, ketoconazole, or selegiline. Surgery is used in some cases of adrenal tumors.
• Diabetes insipidus* in dogs and cats can be central, caused by a lack of antidiuretic hormone (ADH), or nephrogenic, caused by a lack of response of the kidneys to ADH. Neither form is common. Central diabetes insipidus (CDI) is usually idiopathic, but can also be caused by head trauma or tumors of the brain. Nephrogenic diabetes insipidus (NDI) can be primary (hereditary) or secondary (caused by a variety of metabolic and renal diseases, including Cushing's syndrome and pyometra). Because the disease is characterized by an inability to concentrate urine, the most common sign is increased drinking and urinating. Treatment of CDI is to use desmopressin, a synthetic analog of ADH. Treatment of NDI is to treat the underlying cause, if any.
• Acromegaly (also known as hypersomatotropism) is a hormonal condition resulting from over-secretion of the growth hormone somatotropin from the pituitary gland. The hormone is responsible for growth from birth to adulthood. Normally in adulthood, the growth plates of the bones close and the secretion of the hormone slows considerably. Because the bone plates close when entering maturity, the continued growth of acromegaly is not of normal proportions. Most canine sufferers of the disease are unspayed females but the condition can come about with use of medications containing progesterone. Acromegaly patients often also have diabetes mellitus. There is a transient form of acromegaly which can affect females at the diestrus portion of the reproductive cycle. This condition is brought about by the mammary glands excreting excess growth hormone, which is triggered by progesterone from the ovaries. As with non-transient acromegaly, spaying is necessary. The symptoms can include overgrowth or enlargement of gums with wide spaces between teeth, increased drinking, increased urination, thickening of the skin and skin folds, enlargement of the tongue and excessive panting. Acromegaly is also possible from a somatotroph adenoma. The hormone somatostatin can also be useful in treatment. Since hypothyroidism is connected with the release of excess growth hormone, hypothyroidism can be mistaken for acromegaly.