Cushing’s disease in dogs, also known as hyperadrenocorticism (HAC), is a syndrome that occurs when the dog’s body is under the influence of too many steroids, whether natural steroids produced in the body or steroid medications that were given to treat another condition. .
The most common symptoms of Cushing’s disease in dogs include:
- Excessive thirst (polydipsia)
- Excessive urination (polyuria)
- Excessive hunger and eating (polyphagia)
- excessive panting
- Muscular weakness
- Abdominal distension (“pot-bellied appearance”)
- Hair loss or baldness (alopecia)
- Slow hair growth
- Thin skin
- Blackheads (comedones)
- Lethargy
In addition to these symptoms, dogs with Cushing’s disease are prone to high blood pressure (hypertension), urinary tract infections, chronic skin infections, concurrent diabetes, thick skin plaques called calcinosis cutis, and blood clots (thromboembolism). Because the ligaments weaken, the anterior cruciate ligaments (ACL) in the knee can tear. Over time, stomach ulcers can develop in untreated dogs.
Fortunately, Cushing’s disease tends to progress quite slowly, so it will likely be months, or even years, before a dog with the syndrome suffers from many of these symptoms.
Adrenal function must be correct
Natural steroids, also known as glucocorticoids or cortisol, are essential hormones produced by the adrenal glands that play a role in metabolism, immunity, stress response, and other important bodily functions. Quiet The adrenal glands, which produce too few steroids, create a life-threatening condition called Addison’s disease in dogs. hyperactive Adrenal glands producing too many steroids cause Cushing’s disease in dogs. Life is definitely better when adrenal function is proper!
The preferred term for Cushing’s disease or hyperadrenocorticism in dogs is “Cushing’s syndrome,” as Cushing’s syndrome is complicated and there are four different types that cause the same set of symptoms:
- Pituitary-dependent hyperadrenocorticism (PDH). This is the most common form of Cushing’s disease in dogs, responsible for 85% of cases. It is caused by a tumor (usually benign) in the pituitary gland that creates too much adrenal-stimulating hormone, which then results in overproduction of cortisol by the adrenal glands. Since the pituitary gland is very close to the brain, neurological disorders can occasionally occur, depending on the size and type of tumor.
- Adrenal tumor. This type of HAC occurs when a primary functional tumor forms in an adrenal gland, resulting in overproduction of cortisol.
- Iatrogenic HAC. This is caused by the administration of steroid medications, either oral or topical, and is clinically indistinguishable from naturally occurring Cushing’s disease.
- Atypical HAC. This happens when a lack of an enzyme causes the buildup of cortisol (sex hormones) precursors, producing exactly the same symptoms as all other forms of HAC.
Diagnosis of Cushing’s disease
No test for Cushing’s disease in dogs is perfect, but the most commonly used test is called the low-dose dexamethasone suppression test (LDDST). This is a “challenge” test, in which the dog is given a dose of intravenous steroid and its response to that challenge is measured. Due to the negative feedback systems responsible for maintaining balance in the body, a normal dog’s natural cortisol production will be suppressed when the brain recognizes the excess steroids in circulation. But if a dog has Cushing’s disease, his overactive adrenal glands do not have the ability to suppress cortisol production.
This test requires an 8-hour stay in the hospital, with an initial blood sample drawn before the steroid is injected and additional samples drawn four and eight hours after the injection. Dogs without Cushing’s disease will have very low cortisol levels at four and eight hours. Dogs with Cushing’s disease will still have elevated cortisol levels at four and eight hours because they cannot suppress cortisol production.
The LDDST test can be a bit expensive. There is a less expensive and less invasive preliminary screening test that you can perform first, in hopes of avoiding the cost and stress associated with LDDST. It’s called a urinary cortisol:creatinine ratio (UCCR) test. It is done with a urine sample that you collect at home during a time of little or no stress for your dog (stress produces false positive results). And here’s the deal: If the UCCR test is normal, your dog does not have Cushing’s disease. However, if the UCCR test result is abnormal, it just means that your dog could has Cushing’s and must go ahead with the LDDST after all.
Determining Cushing’s type
Once your dog has been diagnosed with Cushing’s disease, the next step is to determine if it is PDH or an adrenal tumor. While additional blood tests may be performed, most doctors recommend an abdominal ultrasound as a next step. In PDH, both adrenal glands are usually symmetrically enlarged. With an adrenal tumor, one adrenal gland is usually enlarged by the tumor and the opposite gland is small. Ultrasound can often also identify neoplastic (cancerous) changes in the architecture of the affected gland.
For iatrogenic Cushing’s disease, a good medical history is of utmost importance. Is the dog taking oral steroids? Is topical cortisone applied chronically for dermatological disorders? Is the dog’s owner (or anyone else in the household) using topical cortisone products that the dog may be licking? To confirm iatrogenic Cushing’s disease, an adrenocorticotrophic hormone stimulation test (ACTH Stim) should be performed. This is another “challenge” test. This time, an initial blood sample is drawn and ACTH is injected, and a post-injection sample is drawn one to two hours later. Dogs with normal adrenal glands, PDH or AT, will show an increase in cortisol production after this adrenal stimulation. If the symptoms and history match, and ACTH Stim does not show an increase in cortisol levels, the diagnosis is iatrogenic Cushing’s and the external source of steroids should be slowly withdrawn. Slow withdrawal is important as the adrenal glands will have become a little numb as there has been a lot of steroids floating around and they need time to get back to full function.
If all of this isn’t complicated enough, let’s talk about atypical Cushing’s disease. These dogs have all the symptoms of Cushing’s syndrome, but all their diagnostic tests come back normal. When this happens, the last stone to clear is to perform an atypical Cushing’s test, which requires an ACTH Stim test with measurement of sex hormones before and after stimulation. An increase in sex hormones after ACTH stimulation is indicative of atypical Cushing’s.
Treatment for Cushing’s disease
Because Cushing’s disease progresses so slowly, some veterinarians and pet owners will choose not to treat it until the dog’s symptoms become problematic. As long as you and your veterinarian closely monitor your dog’s health, this is an acceptable approach early in the course of the disease.
Trilostane has become the treatment of choice for PDH. It is a synthetic steroid equivalent that inhibits an enzyme, resulting in the suppression of natural cortisol production. Side effects are generally mild (lethargy, vomiting, diarrhea), but careful monitoring is important, since too much trilostane can cause excessive adrenal suppression, which can be fatal. Monitoring requires repeating ACTH Stim testing at intervals recommended by your veterinarian.
Mitotane (Lysodren) is another treatment for PDH that actually destroys adrenal tissue, thus decreasing the amount of cortisol that can be produced. Side effects can be mild or severe and include weakness, vomiting, diarrhea, and loss of appetite. Treatment with Lysodren also requires close monitoring with repeated ACTH Stim testing, as inadvertent destruction of too much adrenal tissue creates a life-threatening situation and the damage may be irreversible.
Radiation therapy may be considered for dogs with large pituitary tumors that cause neurological deterioration.
For atypical Cushing’s disease, Lysodren is the treatment of choice as it suppresses sex hormones and cortisol. Trilostane does not.
The treatment of choice for an adrenal tumor is surgical removal of the abnormal adrenal gland (unilateral adrenalectomy). Unfortunately, this is a difficult surgery with the possibility of serious complications (bleeding, thromboembolism) both during and after the procedure. The best candidates for surgery are dogs with small tumors with no evidence of tumor invasion into surrounding blood vessels and no evidence of cancer spread to the liver or lungs (metastasis).
For dogs that are not candidates for surgery for any reason, palliative therapy with Trilostane or Lysodren may help. Radiation therapy is another option for these dogs.
If these treatments and their associated dangers make you cringe, melatonin and lignan supplements are a couple of alternative treatments you can try. They are surely less harmful, but unfortunately also less effective.
Melatonin is a neurohormone produced by the pineal gland; It inhibits certain enzymes, resulting in decreased cortisol production. Flaxseed oil with lignans has antiestrogen activity so it may be useful for atypical Cushing’s disease. Melatonin and lignans can be used together.
You can read about ketoconazole and selegiline (Anipryl) as alternative treatments for Cushing’s disease. However, it is said that its effectiveness is so low that you would really be wasting time and money.
It’s time to think about it
As you can see, Cushing’s disease in dogs is complicated. The treatment options can be scary. The expenses associated with treatment and necessary follow-up add up quickly. The advantage is that Cushing’s disease usually progresses so slowly that dogs can live with it for a long time before it causes problems. If your dog is diagnosed with Cushing’s disease, talk to your veterinarian about what may be the best option for you and your dog. To treat or not to treat? If it is treatment, what treatment? Yeah No trying, how can you carefully monitor your dog’s health while living with Cushing’s disease? Frequent physical examinations, blood tests, urinalysis, and blood pressure measurements should be considered. These are all important details that should be seriously considered to make the best decisions for your dog.
