Cushings Disease in Dogs
" Cushings disease in dogs is the term used to describe “hyperadrenocorticism”. Cushing’s disease is the chronic overproduction of a hormone called “glucocorticoid”, which is produced by the adrenal glands. These glands in turn are stimulated by another hormone,called ACTH, which is released by the pituitary gland. The pituitary gland is also called the “master gland” of body. This condition is complex and common in middle aged dogs age 7 – 12 years. There is a range of symptoms associated with Cushing’s disease including polydipsia (increased thirst), polyuria (frequent urination in large volumes), alopecia (hair loss), lethargy, heat intolerance, enlarged abdomen, panting, muscular weakness and recurring urinary tract infections. Several screening tests are required to make a diagnosis. Treatment involves the use of different adrenolytic agents, enzyme inhibitors and ketaconazole. Surgery is indicated in some cases. "
Pathogenesis of Cushings disease in Dogs:
Canine Cushings disease is found in two forms,
- Pituitary
Dependent; The pituitary gland is considered the “master
gland” in a dog’s body. It controls all hormonal secretions and
glandular activity. It controls the of adrenal gland secretions of the
“Adrenocorticotrophic Hormone” (ACTH). ACTH stimulates the adrenal
gland to release glucocorticoids. Cushing’s disease in dogs is mostly
pituitary dependent. Tumors and hyperplasia (increased number of normal
cells) of the pituitary gland results in increased secretions of ACTH,
which causes overproduction of glucocorticoids by the adrenal gland. It
is proven now that 82% of all reported Cushing’s disease cases in dogs
are pituitary dependent.
- Adrenal Dependent; Any abnormality in the adrenal glands, like that of a tumor, infection or anything causing pressure, may result in the increased production of glucocorticoids, which causes canine cushing’s disease. Along with adrenal abnormalities, high doses of steroids are administered for any other disease, surely causes Cushing disease dogs. It is estimated that 14% of all hyperadrenocorticism cases are due to adrenal diseases & 4% of those are due to high doses of steroids reported as in USA.
Signs and Symptoms of Cushings Disease in Dogs
Cushing’s disease is more common in middle aged and older dogs, usually age 7 – 12 years. Several dog breeds like poodles, boxers, boston terriers, beagles and dachshunds are more at risk.
As far clinical signs and symptoms are concerned, canine Cushing’s disease is a complex condition and is difficult to recognize. The most common signs are polydipsia (increased thirst) and polyuria (frequent urination) in larger volumes. Affected dogs consume more water which is surely correlated with frequent urination. The abdomen appears enlarged, appear obese and and will look like the dog has a “Pot – Belly”. Dogs with Cushings pant and get tired easily, both when involved in a low level of exercise and when running. Muscular weakness is another sign, which in later stages of the disease, leads to ataxia (failure of muscle coordination) in dogs.
Urinary tract infections are common and reoccur after recovery, a problem that leads to renal failure (Kidneys) in most cases.
Along with these signs, Cushings disease dogs may result in dermal (skin) signs. Alopecia (hair loss), rashes, hyperpigmentation and seborrhea (flaking, dandruff) are some common signs. Other skin complications such as the appearance of mineral crystal deposits on the skin and degenerating skin is seen in severe cases.
Diagnosis of Cushings Disease in Dogs:
Two different forms of cushings disease in dogs, the spectrum of clinical signs and the behavior of affected dogs makes Cushing’s disease hard to diagnose. The only possible way to diagnose Cushing’s disease is with a screening test. Screening tests like “low – dose dexamethasone suppression” (LDDS), an ACTH stimulation test, Urine Cortisol/Creatinine Ratio (UCCR) and measurement of ciALP are some examples.
Differentiating (determining) the form of canine Cushings disease, i.e. pituitary dependent or adrenal dependent is essential in terms of selecting a treatment plan. In this regard, adrenal & pituitary radiographic imaging is best to tell the difference. Any tumors, degeneration or abnormality is usually helpful in describing a form of Cushings disease in dogs.
Treatment of Cushings Disease in Dogs:
After a confirmed diagnosis for any form of canine Cushing’s disease, a treatment plan is usually calculated according to age, breed and most importantly, the physiological condition of the body. When treating a pituitary dependent form of canine cushing's disease, an adrenolytic agent called mitotane is used. In the beginning a dose of 25 – 50 mg/Kg/Day is administered for 8 – 10 days. At the same time the veterinarian will monitor signs like vomiting, diarrhea and anorexia (avoidance of food). Once these signs along with reduced urination and water consumption are noted, glucocorticoids are administered. This is used as a technique for balancing hormonal secretions in the body.
Ketaconazole is another option, which acts as “steroid biosynthesis inhibitor” (SBI). Oral doses of 5 mg/kg are administered orally for 7 days initially and if no side effects like anorexia and jaundice are noted, the dosage is increased to 10 – 15 mg/Kg, depending upon monitoring and screening results, which need to be conducted every 6th day.
Surgical removal of tumors like adrenal adenomas and adenocarcinomas may be required in some cases. Surgical procedures are costly and usually not very effective due to the involvement of two different glands and their respective secretions, which usually causes severe secondary complications. Radiation therapy is an alternative to surgical procedures. Radiation therapy is considered very effective, but is very costly, time consuming (3 Months) initially followed by long term follow up of the pituitary gland to look for any recurring cancers.
There is a homeopathic product available that can naturally help to support the adrenal glands called Cushex . While no substitute for conventional medicine, it could provide additional support for a dog that is suffering from Cushing's disease. It contains ingredients such as Dandelion (anti-oxidant) and Burdock (blood sugar, waste removal from the body) which can be of help. The manufacturers site contains additional research and ingredient based clinical studies.
References:
J. Morris, Small Animal Oncology (Blackwell Science 2001)
Dobson, J.M., Text Book of Small Animal Medicine (W.B. Saunders London. 2001)
