- in Dog Health
Cushing's disease, or hyperadrenocorticism, can affect any animal of any age, although it is most common in dogs and horses. It is incurable, but can be treated to reduce the symptoms. Here's what you need to know.
Cushing's disease causes the adrenal cortex part of the kidneys to secrete high levels of cortisol into the blood. Cortisol is a corticosteroid hormone that increases blood pressure and blood sugar levels as a reaction to the adrenocorticotropic hormone (ACTH) released from the pituitary gland, usually during highly stressful situations.
In normal situations, the ACTH would alter the amount of cortisol in the blood, either increasing or decreasing, as necessary. With Cushing's disease, the ACTH is unable to react and cortisol pours into the blood stream continuously.
The symptoms of Cushing's disease are the same, regardless of how it's caused. The disease has three separate causes:
- A tumorous growth on the pituitary gland is the most common cause. The growth causes excess production of ACTH, increasing the amount of cortisol released into the blood stream.
- A tumorous growth on the adrenal gland is also common. The adrenal gland produces cortisol, so such a tumor causes excessive cortisol to be made and pumped into the circulatory system.
- Prolonged use of corticosteroid drugs can also cause Cushing's disease to develop. These drugs are used to treat other complaints, usually skin-related conditions such as flea allergic dermatitis.
They affect the cortisol hormones and the animal's body tries to compensate by reducing the amount of cortisol and ACTH produced by the adrenal and pituitary glands. The body finds it difficult to handle the constantly increasing amount of corticosteroid within the blood and results in Cushing's disease.
The symptoms develop over time and increase if the disease is not effectively treated. It is important to catch Cushing's disease as early as possible so that treatment may begin. The symptom list is extensive:
- Increased thirst (polydipsia) is generally one of the first symptoms to appear
- Increased urination (polyuria) is caused by the excessive thirst
- Increased appetite (polyphagia) can cause even well-behaved animals to steal food to sate their appetite
- Weight gain caused by the polyphagia
- A lack of enthusiasm to exercise (lethargy), which may also contribute to weight gain
- Diabetes mellitus caused by the body's inability to react to the high levels of insulin and blood sugar
- Vomiting & diarrhea, which may not be a direct symptom of Cushing's disease; hormone levels can have an effect on the gastrointestinal tract
- Bloating, so the stomach begins to bulge with an almost pot-bellied appearance, due to retaining gas and water
- Changes in coat condition, with the hair becoming brittle and weak. Bald patches can appear with excessive grooming
Cushing's disease is easy to diagnose. The vet will examine the history of symptoms to determine whether Cushing's disease is possible and, if so, will schedule tests:
- Blood tests will show higher levels of liver enzymes, glucose and cholesterol, and the white blood cell count will be lower than normal
- Urinalysis will measure the amount of protein and the specific gravity of the urine. High protein levels and low specific gravity are indicators
- Radiographs show the size of the organs affected and the size and location of any adrenal tumors
- CT scans can show any tumors on the pituitary gland, but are rarely performed on animals because they are expensive
- ACTH stimulation tests are one of the best ways to prove Cushing's disease. The vet takes a blood sample and measures the amount of ACTH and cortisol. They take a second sample after an injection of ACTH and a two-hour wait. A dramatic increase in cortisol levels confirms Cushing's disease
- Dexamethasone suppression tests can be more reliable than ACTH stimulation tests. In this case, the animal fasts for eight hours before the vet takes a blood sample. The vet injects small doses of dexamethasone and takes a second blood sample eight hours later. A healthy animal suppresses the cortisol, so Cushing's disease is confirmed if it is still present. Pituitary-related Cushing's will show a small form of suppression whereas adrenal-related Cushing's will show high cortisol levels
Once the vet diagnoses the type of Cushing's disease, treatment can begin depending on the animal's age and current health. Although Cushing's is incurable, it is controllable. Diabetes may accompany the condition, so insulin injections may be needed in addition to any other treatment.
Surgery is one of the best options for handling Cushing's disease. By removing tumors, hormone production levels will begin to return to normal. Sadly, though, many tumors reoccur. Pituitary tumors are the most difficult to remove and may require a specialist.
An alternative is chemotherapy, though it's not a common option because of the adverse side effects. It can help reduce the size of tumors, and is frequently suggested in the presence of pituitary tumors, where surgery may not be possible.
In general, research is key when picking a pet reptile. There are hundreds of great species to choose from and you're bound to find one that meets your needs.