Cushing's disease is a disorder of the adrenal glands in which excessive adrenal hormones are produced. The cause of hyperadrenocorticism (HAC) may be abnormal pituitary gland function, tumours of the adrenal gland, “cortisone” therapy or unexplained over-activity of the adrenal gland. Pituitary dependent HAC accounts for about 80% of all cases.
Hyperadrenocorticism is a slowly progressing disease and the early signs are often not noticed. These include increased appetite, increased drinking and urination, reduced activity, and enlargement of the abdomen. As the disease progresses, these signs intensify, and the pet may become fat, pant heavily, and lose hair evenly over each side of the body. In some cases, hair loss may be the only apparent change.
Extensive laboratory tests and radiographs or ultrasound may be needed to diagnose the condition, find its cause and plan treatment. Unfortunately, some patients grow worse despite treatment.
Treatment for Cushing's disease
Control, rather than cure, is the outcome of treatment in most cases of HAC. Treatment consists of a capsule administered either daily or weekly (Vetoryl/Mitotane). Once treatment is started, dogs must be carefully monitored, since the drugs used in therapy may cause underproduction of adrenal hormones and a shock-like state known as an Addisonian crisis.
Treatment of Cushings disease can be expensive. In addition to the cost of the medication itself, the dog’s response to treatment must be assessed by regularly repeating laboratory tests (ACTH stimulation test and blood counts).
If your dog develops any of the following signs after starting treatment please contact us immediately:
• Drinking less than 40mls/kg of water a day in dogs that were drinking excessive amounts (>100mls/kg/day) before treatment
• Vomiting or diarrhoea
• Taking 15 to 30 minutes longer to eat than before start of therapy
• Listlessness, depression, or weakness
• Skin condition worsens
The average life expectancy for dogs with adrenal dependent HAC is 36 months. The average life expectancy for dogs with pituitary dependent HAC is approximately 30 months with younger dogs living longer (i.e., 4 years or more).
Many dogs ultimately die or are euthanised due to complications related to Cushing's disease such as pituitary macro tumour syndrome, pulmonary thromboembolism, diabetes mellitus, infection, etc.
1. Pituitary macro tumour syndrome is a result of the tumour on the pituitary gland expanding into other parts of the brain. The dog will begin showing neurological signs such as aimless wandering, pacing, circling, and behavioural alterations. These signs usually develop 6 months or more after diagnosis.
2. Pulmonary thromboembolism is most commonly seen shortly after treatment. The presenting sign is sudden respiratory distress or difficulty breathing. Once this occurs the prognosis for recovery is grave. It usually requires 7 to 10 days on oxygen therapy if the animal survives.
3. Development of diabetes mellitus is also another potential problem with Cushing's disease. The high levels of steroids in the blood stream can cause insulin resistance. The signs of diabetes are very similar to the signs of Cushing's disease, so it is important to notify us if you notice them returning. Many dogs can have their diabetes controlled for a time with regular insulin therapy.
4. Infections are common in animals with Cushing's disease due to the overproduction of steroids. Steroids suppress the immune system and therefore prevent the animal from fighting off infection. One of the goals of treatment is to lower the animal's blood levels of steroids to prevent this from happening. Urinary tract infections and skin infections are most commonly seen. The more severe and life threatening ones include sepsis and pyelonephritis (kidney infection).
