Cushing's Disease

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What is it?

Cushing's Disease, or Hyperadrenocorticism, is a disorder of the endocrine system, where the adrenal glands release too much cortisol (a natural steroid).

What causes it?

Cortisol is sometimes called "the stress hormone", because it is released in the body in times of stress (physical or mental/emotional). It is produced in the adrenal glands, but these are themselves controlled by the pituitary gland, which releases a hormone called ACTH (adrenocorticotropic hormone) telling the adrenals to make more cortisol. If an adrenal gland malfunctions and starts making excessive amounts of cortisol, or if the pituitary malfunctions and releases excessive amounts of ACTH, the result is the same. In most cases, these are due to secreting tumours (about 85% are in the pituitary, so-called Pituitary Cushing's). There is another form of the disease too, called Iatrogenic Cushing's, which is due to excessively high doses of artificial steroids.

What dogs are at risk?

The disease usually affects adult to elderly dogs.

What are the symptoms?

The symptoms of any kind of Cushing's are the same; as steroids affect a wide range of different systems, Cushing's can have a wide range of different effects. Common symptoms, however, include:

  1. Increased thirst and increased urination.
  2. Increased hunger.
  3. Hair loss, usually causing bald patches on both flanks.
  4. Muscle loss and fat redistribution, resulting in a "pot-bellied" appearance.
  5. Increased susceptibility to infection (especially urinary tract and skin).
  6. Increased susceptibility to diabetes mellitus.
  7. Lethargy.
  8. Dislike of heat or hot weather.
  9. Increased breathing rate, and often increased panting.

How is it diagnosed?

Although the symptoms are quite characteristic, unfortunately there is no test that is 100% accurate in diagnosing Cushing's Disease. The most commonly used tests are:

  1. The Urine Cortisol to Creatinine Ratio (UCCR) Test. This is very good as a screening test, but gives lots of false positive results (in other words, you may get a positive result even if the dog doesn't have Cushing's, but it's very unlikely you'll get a negative test if it does).
  2. The ACTH Stimulation Test, which works by measuring the response of the adrenal glands to the ACTH hormone.
  3. The Dexamethasone Suppression Test (in High and Low Dose forms), which looks to see whether adrenal function is reduced when additional steroids are introduced to the body, which it should be but isn't in Cushing's.

The High Dose test can also distinguish between Pituitary and Adrenal Cushing's.

How can it be treated or managed?

The standard treatment is with medications that temporarily suppress the adrenal gland's ability to make cortisol; with the proper dose, cortisol levels can be managed and kept within the proper range. The active ingredient in these tablets is trilostane, and they are licensed for use in dogs. There is another, related, drug, that permanently destroys the adrenal tissue (mitotane), but this is not licensed and is rarely used, because even a very slight overdose could lead to Addison's Disease.

Can it be prevented?

No, there is no preventative treatment known.

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