Harvey Cushing discovered Cushing's syndrome in the early 1900s. The disease occurs when the hormone cortisol is produced in excessive amounts inside your dog’s body.
Cortisol is usually a good hormone which can help fight infections, maintain blood sugar levels and contributes to keeping your dog calm.
However, cortisol in excessive or low amounts can be dangerous or deadly. The disease occurs mainly in middle-aged and old dogs. Breeds that seem a more prone to Cushing's disease include Yorkshire Terriers, Poodles, Beagles, Dachshunds, Staffordshires, Jack Russells, Boxers and Boston terriers but it can affect any breed.
What causes Cushing's Syndrome?
There is a part of a dog's brain which produces “adrenocorticotropic hormone,” which we will refer to as ACTH. This hormone instructs the adrenal glands to produce cortisol.
Usually, this is regulated by the amount of cortisol already present in the dog. However, Cushing’s syndrome occurs when a dog produces an excess of ACTH, regardless of how much cortisol is already in the body. This excess ACTH leads to the production of excess cortisol.
This disease has two different causes.
The first cause is a benign tumour forming inside the pituitary gland. Known as hypercortisolismis, it is by far the most common version of Cushing's Syndrome, accounting for 80% of the cases.
The second one is when the tumour forms on the adrenal gland, which is called hyperadrenocorticism and accounts for around 20% of all cases.
It can be hard to tell if your dog has this disease as its symptoms can be confused with many other conditions.
The main symptoms can be easily memorised as the five Ps:
- Polydipsia (thirsty all the time)
- polyuria ( excessive urinating)
- polyphagia ( increase in appetite)
- panting, and
- pot-belly (a big liver and the weakening of stomach muscles all contribute to the round shape of your dog’s belly).
Other symptoms may include:
- fat accumulating on the neck and shoulders,
- hair loss,
- unenergetic behaviour,
- inability to sleep,
- muscle weakness,
- no heat cycle in female dogs,
- shrinking of testicles,
- skin getting darker,
- appearance of blackheads on the skin,
- skin getting thinner from the excessive weight,
- bruises (from thin, weakened skin),
- hard white scaly patches on the skin, elbows, etc.
Diagnosis of Cushing's disease
Diagnosis can be difficult; a thorough examination is necessary, and often Laboratory tests will be conducted.
The tests will look for an increase in the dog's level of an enzyme called alkaline phosphatase and a urine test will look for urine that is clearer and richer in protein than usual.
However, even if both of these come back positive, this doesn't mean that your dog has Cushing's disease. The functions of the pituitary and adrenal glands then need to be carefully tested in order to give more specific information.
However, none of the methods of diagnosis are 100% accurate, and diagnosing Cushing's Syndrome can require many expensive tests.
If your dog has shown potential for having the disease, testing the cortisol to creatinine ratio in your dog's urine is a good and inexpensive method to rule out Cushing's as a regular result means your dog hasn't developed this disease.
The problem is that an abnormal ratio can be a symptom of many different conditions, so while it can help rule out Cushing's it does not mean that it is!.
Other tests include LDDS, which stands for low-dose dexamethasone suppression. This method works by testing a sample of blood for cortisol. After this, your dog will be given a dexamethadone injection and the blood tested multiple times.
If the cortisol level doesn't decrease, your dog probably has this Cushing's disease.
Cushing's can be treated in a variety of ways. Surgery can be a fast way to remove the tumour causing the disease, but this is not always possible.
Medication does also exist and is primarily used to treat symptoms caused by a tumour on the pituitary gland, or symptoms on an adrenal gland which has spread to other parts of the body and can't be removed surgically.
Surgery may be a solution in some cases but it is crucial to determine where the tumour is and to what areas it spread. If the disease originates from a tumour on the dog's adrenal glands, and if it hasn't spread to other areas, a surgery might be able to remove it.
The cheapest used drug is mitotane but it does come with some significant side effects including:
- loss of appetite,
- lethargy and weakness.
Once the correct dose is found your pet's decreased water intake is a sign that the treatment is working. It takes 4-6 months for all of the signs of Cushing's disease to fully dissipate when lysodren is successful. It is not unusual for the pets required dose to change over time so your vet will look to re-run tests and adjust the dosage throughout this period.
Your pets water consumption and urination habits should return to normal much faster than that. Hair is often the slowest thing to return to normal.
Trilostane (Vetoryl, Modrenal)
The most common drug recommended by vets is trilostane. Its effects are quite similar to lysodren although it does not appear to be as severe. Pre-marketing research indicated that trilostaine should produce less adrenal gland damage (Addisonian reaction) than Lysodren, however, this now appears to be untrue.
l-deprenyl (Anipryl), became available in 1997 as a spin-off of human Parkinson disease research. It has fewer and less severe side-effects compared to Trilostane and Lysodren. As little as 1 in 20 dogs receiving it will experience any side effects, which include gastrointestinal upsets, restlessness, disorientation or occasional hearing problems.
On the downside, Anipryl is only effective if the root of your dog’s Cushing's problem is a pituitary tumour, but not very effective if your pet’s problem is caused by adrenal gland tumours.
Anipryl works by regulating dopamine, a neurotransmitting chemical in your dog’s brain and pituitary gland. When dopamine levels are high, portions of the pituitary gland stop send ACTH signal messages to your pet's adrenal glands telling them to produce cortisol.
The main reason this is not used more often is down to its effectiveness. At best, it seems that Anipryl is an effective alternative to lysodren therapy in only 20–40% of canine Cushing's patients.
Ketoconazole is an anti fungal drug that also affects the endocrine gland system. It is only effective in about half of the dogs with Cushing's disease. Additionally, improvements seen on ketoconazole are often incomplete or temporary.
For these reasons it is generally not the first choice of veterinarians or physicians in Cushing's disease treatment but it is sometimes given when other drugs are ineffective or produce too many side effects.
When it works, It seems about equally effect for pituitary and the adrenal forms of Cushing's.
Life expectancy for dogs with Cushing's Disease
Should your dog no respond to the treatments, their life expectancy is still fairly good but depends on which tumour did the disease originates from. If the disease is adrenal-gland dependent, he is expected to live around 36 months. If the disease is pituitary-gland dependent, the expected life expectancy is around 30 months, considering that younger dogs will live longer after being diagnosed.
Even with this disease, you dog will be able to live a normal, happy life, although he will depend on his medication all the time. Take good care of your dog. Give him proper medication regularly and don't leave him out of your sight for longer periods of time. Keep an eye on his symptoms and take him to s vet as soon as you see anything strange. If you do all that, he will be able to live the rest of his life happily.
Make sure your dog gets to live those years happily. He deserves it.