Cushing’s disease in dogs is caused when their bodies make too much of a hormone called cortisol. This chemical helps them respond to stress, control their weight, fight infections, and keep their blood sugar levels in check. But too much or too little of it can cause problems.
Dogs, cats, and horses, as well as humans, can get Cushing’s disease. It is more commonly found in dogs than in cats or horses.
“Cortisol is one of the body’s natural steroids,” says Ann Stohlman, V.M.D., a veterinarian in FDA’s Center for Veterinary Medicine, adding that a normal amount of cortisol helps the body adapt in times of stress. Cortisol also helps regulate proper body weight, tissue structure, skin condition, and other features of good health.
But too much cortisol weakens the immune system, leaving the body vulnerable to other diseases and infections.
Pituitary dependent hypercortisolism, also known as Cushing’s disease, is a direct cause of excessive levels of the stress hormone cortisol triggered by a non-cancerous pituitary tumour. Normally, the pea-sized gland at the base of the brain (the pituitary), produces an adrenocorticotropic hormone, or ACTH, whose role is to stimulate the adrenal glands near the kidneys to produce the stress hormone.
Very few dogs with Cushing’s disease have a tumour in one of the adrenal glands which may very likely be cancerous. This type Cushing’s is called adrenal-dependent Cushing’s and results from an increase in cortisol production by the tumor in the adrenal gland. Roughly 100,000 dogs are diagnosed with Cushing’s disease in the United States every year. Most dogs that are diagnosed are six years or older in age, but it can also occur in dogs younger than four years.
Diagnosing your dog for Cushing’s disease:
There’s no single test that is used to diagnose Cushing’s disease in dogs. History, results of initial blood and urine tests and physical exam often provide strong clues for the presence of Cushing’s disease. Signs can include an increase in platelet or white blood cell count, increase in the liver enzyme alkaline phosphatase, increased blood sugar (although not as high as the sugar levels of diabetic patients), dilute urine, and increased cholesterol. Urine creatinine/cortisol ratio, low dose dexamethasone suppression test, high dose dexamethasone suppression test, and an ACTH stimulation test are some of the specific tests for Cushing’s disease in dogs.
- ACTH stimulation test. It measures how well the adrenal glands work in response to a hormone called ACTH that usually prompts them to make cortisol. The vet will take blood samples before and after your dog gets a shot of ACTH to see how the hormone affected them.
- Low dose dexamethasone suppression (LDDS) test looks at how your dog’s body works with a man-made version of cortisol, called dexamethasone. Blood samples before and after they get a shot of the hormone to help the vet see what’s going on.
When large amounts of cortisol in the body inhibit the immune system, dogs with Cushing’s disease are prone to bacterial infections, particularly bladder infections. A urine culture may be necessary to diagnose the infection because they may not show typical signs such as difficulty to urinate.
Dogs affected with Cushing’s disease may have enlarged adrenal glands or liver (both if pituitary-dependent, or just one if the dog has an adrenal tumor). Your veterinarian may use ultrasounds or use x-rays to check the adrenal glands or liver. The adrenal glands cannot always be seen during an ultrasound exam when diagnosing Cushing’s disease in dogs. In case of an adrenal tumour, the tumour can often be seen growing into major blood vessels close to the adrenal gland or it may be seen in the liver as it spreads from the tumour.
Cushing’s disease in dogs can be tricky for a vet to diagnose because it has the same symptoms as other conditions. The sooner you let your vet know of any changes that your dog is going through, the better.
Surgery can cure dogs of the problem in most cases. If your puppy can’t have an operation, they can control their cortisol levels through medication
What are the common symptoms of Cushing’s Disease?
Middle-aged to older dogs are the one’s that mostly suffer from Cushing’s disease. The disease develops slowly and the early signs are not always noticeable. Take your dog to the vet if your dog appears to be:
- drinking more water than normal
- urinating more often
- eating excessively
- slowed down
- panting excessively
- having fragile or thin skin
- losing hair
- experiencing skin infections
- growing a “potbelly”
The abnormal spike in production of cortisol causes symptoms such as increased appetite, pot-bellied appearance, hair loss, and increased urination and drinking and called polyuria and polydipsia (PD/PU). Hair loss caused by Cushing’s disease occurs on the body, sparing legs and the head. Unlike other skin diseases, the skin is usually not that itchy. When picking up a fold of skin on a dog with Cushing’s disease, it is possible that you will notice that the skin is thinner than normal. Your dog may have fragile blood vessels and may bruise easily. Cortisol affects the function of many organs in the body and the signs of Cushing’s disease are very different. If untreated, a pituitary tumour could grow large enough to press on your dog’s brain causing neurological symptoms such as difficulty seeing or walking, or other conditions including seizures or diabetes. Dogs that are given drugs like prednisone can develop signs that look like Cushing’s disease (called iatrogenic Cushing’s). If your pet is showing any of these symptoms, consult your local veterinarian.
The Two Types of Cushing’s Disease in Dogs:
Naturally occurring Cushing’s disease is either adrenal-dependent or pituitary-dependent.
The pituitary makes a number of hormones, including adrenocorticotropic hormone (ACTH). When the pituitary tumour causes overproduction of ACTH, it travels through the bloodstream to the adrenal glands and stimulates them to produce more cortisol than the body needs.
- Pituitary dependent. This form is the most common, affecting about 80% to 90% of the animals who have Cushing’s. It happens when there’s a tumour in a pea-sized gland at the base of the brain, called the pituitary.
- Adrenal dependent. This type comes from a tumour in one of the glands that sit on top of the kidneys, called adrenal glands. About 15% of diagnosed dogs will have this type.
Cushing’s disease is treated based on the type.
Blood tests are prescribed by veterinarians to diagnose Cushing’s disease in dogs and to differentiate between disease caused by the pituitary or the adrenals. They may also use an ultrasound or xrays to help detect a tumour on an adrenal gland.
Another kind, called iatrogenic Cushing’s syndrome, occurs in dogs that have been taking steroids for a long time.
Treating Cushing’s disease:
When Cushing’s disease is a direct result of a tumour on your pet’s adrenal glands, your vet might be able to remove it surgically, and cure your pet of the problem. But if the tumour has spread to other parts of their body or they have other health problems, surgery may not be an option.
Usually, a dog is able to live a normal, active life with medication to treat the condition, even though they’ll need it for the rest of their life. Medicines are best for dogs with Cushing’s syndrome caused by the pituitary gland or for those with a tumour on their adrenal gland that cannot be removed with surgery.
The most common drug is trilostane (Vetoryl). Mitotane (Lysodren) is an outdated drug that veterinarians don’t prescribe much anymore. It may cost less, but it comes with numerous side effects as well. Your pup will need regular blood tests and checkups to make sure their treatment is working.
Veterinarians have often used a human chemotherapy drug, Lysodren (mitotane), “off-label” to treat Cushing’s in dogs. Lysodren destroys the layers of the adrenal gland that produce cortisol. It requires careful monitoring and can have severe side effects.
If your pet has iatrogenic Cushing’s syndrome, your vet can try gradually stopping steroids. But the chances of their original condition (that was being treaed by the sterioid) will come back.
Although Cushing’s disease in dogs is typically a lifelong condition, it can usually can be managed with medications. “It’s important for a veterinarian to see the dog regularly and do blood tests,” Stohlman says. “Monitoring blood tests and response to treatment help determine the right dose, which may need to be adjusted periodically.”
Frequent veterinary checkups and blood tests are usually required in the first few months after starting treatment and then every few months after that, depending on the dog’s response to treatment and tolerance to the medication.
Vetoryl (trilostane), approved by the FDA in 2008 is the only drug approved to treat both pituitary- and adrenal-dependent Cushing’s in dogs. This prescription drug works by stopping the production of cortisol in the adrenal glands. Vetoryl should not be given to a dog that
- has kidney or liver disease
- takes certain medications used to treat heart disease
- is pregnant
Common side effects of the drug are reduced appetite, lack of energy, diarrhoea, vomiting, and weakness. More serious side effects include : bloody diarrhoea, collapse, severe sodium/potassium imbalance, destruction of the adrenal gland, in death. In 2014, with input from CVM, the manufacturer updated the information about patient monitoring and side effects on the package insert. Although not proven to be caused by Vetoryl, some additional side effects reported to CVM and now included on the package insert are adrenal insufficiency, shaking, elevated liver enzymes and elevated kidney tests.
Only one other drug, Anipryl (selegiline), is FDA-approved to treat Cushing’s disease in dogs, but only to treat uncomplicated, pituitary-dependent Cushing’s.
“Off-label,” or “extra-label,” means veterinarians can legally prescribe human drugs to animals for uses not listed on the label, or for other species or at different dosage levels from those listed on the label. But because dogs may react unpredictably to human drugs, says Stohlman, it’s beneficial to have treatments available that have been studied in dogs and approved specifically for them.
“Treating Cushing’s is a balancing act,” Stohlman says. “But dogs with the disease can live a good life if they are monitored closely by a veterinarian and the owner is diligent about bringing the dog in for blood work and checkups, watching for side effects and giving the medication as directed.”
How is Cushing’s disease in dogs treated?
Oral Medication: Lifelong oral medication is often prescribed for pituitary-dependent Cushing’s disease to help manage the symptoms. The most common drugs used to treat Cushing’s disease are Trilostane and o,p’-DDD (also called Mitotane or Lysodren). The initial treatment of o,p’-DDD, called induction, is initially given daily or twice daily for about a week (sometimes more, sometimes less), but it can have serious side effects so pets being treated for Cushing’s disease must be closely watched. After induction o,p’-DDD is given less often, usually once or twice weekly for the life of the pet. Some pets will have a recurrence of signs of Cushing’s disease later in life, even though they are receiving o,p’-DDD. Trilostane tends to have fewer side effects than o,p’-DDD and can be easier to manage, however, it is more expensive. For pets with adrenal dependent Cushings, o,p’-DDD and Trilostane are not as effective in reducing symptoms as it is in pets with pituitary-dependent Cushing’s disease. Discuss with your veterinarian which treatment is best for your pet.
Radiation: Radiation may be used to shrink the size of a pituitary tumour. This treatment is most effective on small tumours to help reduce the symptoms of pituitary-dependent Cushing’s disease.
Surgery: Treatment of adrenal dependent Cushing’s disease is by surgical removal of the affected adrenal gland. Adrenal gland tumours, if cancerous, can spread to other parts of the body in which case all cancer cannot be removed by surgery. Medical treatment may be given before surgery to reduce hormone levels before surgery. Trilostane may be effective in controlling the signs of Cushing’s in dogs with adrenal tumours but is not a definitive treatment.
Transsphenoidal surgery is used to remove a pituitary tumour. The surgeon uses an exoscope, a long tube with a light at the end for magnification and illumination, to reach the pituitary through the soft palate in the mouth to access the base of the skull where the pituitary is located. Surgical removal of the tumour generally eliminates the need for lifelong medication.
The most important thing you can do is to Keep a close watch on their behaviour and follow their treatment plan. Keeping track of the symptoms and giving them the right medication doses at the right time will get you a long way with preserving your dog’s health. You and your vet can work together to help them live a happy, healthy life.