First Rule Out High Cortisol Levels in Hyperthyroid Dogs

By Tess Thompson



Cortisol is often referred to as a ‘stress hormone’. This is because its secretion by the adrenal glands is related to the stress factor. In addition, it also affects blood pressure, blood sugar and is vital to the immunosuppressive actions of the dog’s body. The synthetic form of cortisol, known as hydrocortisone, is used to treat inflammatory diseases, allergic reactions and to supplement deficiencies of the endogenous cortisol.

Levels of cortisol in the body change according to the need of the body. They also vary according to the day-night cycle - the levels are at their peak early in the morning and lowest about 2 to 3 hours after sleep time. Damages to the pituitary or adrenal glands can disturb the production of the hormone to cause conditions like Cushing’s disease (hyperadrenocorticism) and Addison’s disease that require immediate attention of the dog owners. These glands are the two endocrinal glands that are vital to endogenous production of cortisol in the body.

Although the signs of both are the same, medical experts tend to differentiate Cushing’s disease in a dog from Cushing’s syndrome. The former refers specifically to a tumor in the pituitary gland that causes an excess of the hormone, ACTH in the body. Cushing’s disease in a dog is referred to as secondary hyperadrenocorticism in dogs.

Diagnosis of hyperadrenocorticism involves physical examination and routine blood tests. Symptoms of hyperadrenocorticism tend to mimic a number of other endocrinal, liver and kidney disorders. Vomiting, loss of appetite, lethargy, hair loss and skin problems are some of the symptoms that are common to hyperadrenocorticism and hyperthyroidism.

Veterinarians usually prefer to rule out the prevalence of hyperthyroidism before proceeding with treatment for hyperadrenocorticism. For this purpose, a series of specific tests are performed to establish cortisol levels in the dog’s body. Some of the tests that might be required include:

  • Complete blood count
  • Complete analysis of urine
  • Complete chemistry profile
  • Abdominal x-rays and ultra sound examination
  • Complete thyroid profile

The data collected by the veterinarian determines whether the various symptoms are being caused by high levels of cortisol. Once it has been confirmed that the cortisol levels are the culprit, further tests like Adrenocorticotropic Hormone (ACTH) Stimulation Test, Low-Dose Dexamethasone Suppression Test, Urine Cortisol-Creatinine Ratio, High-Dose Dexamethasone Suppression Test and /or Plasma ACTH Measurements need to be undertaken. These tests establish firmly whether the symptoms are due to hyperthyroidism or Cushing’s disease. These tests also determine whether the condition is due to adrenal dysfunction or pituitary malfunction.

Both Cushing’s disease and hyperthyroidism are serious conditions that can affect dog behavior in a big way. Cushing’s disease is a life threatening condition and requires constant monitoring if you want to ensure that your pet has a comfortable life.

References:
http://en.wikipedia.org/wiki/Cushing's_syndrome
http://en.wikipedia.org/wiki/Cortisol

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