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What is Cushings Disease?
Cushing's disease (otherwise known as 'hyperadrenocorticism') is a disorder that mainly affects dogs, but uncommonly can also occur in cats. It occurs when the adrenal glands (two small glands in the body, one located just by each kidney) overproduce a natural steroid called cortisol. It can also occur if your dog is given too many artificial steroids, such as prednisolone, but the disease is then called 'iatrogenic Cushings'.
Cushing's usually occurs due to a benign tumour in part of the brain (the pituitary). This tumour produces a hormone which causes the adrenal glands to become overactive, enlarged and produce excessive amounts of cortisol.
Cushing's may also occur if there is a tumour in either adrenal gland, causing that gland to overproduce cortisol which then results in the other adrenal gland shrinking and becoming redundant. This adrenal tumour may be benign or malignant. If it is malignant, there is a chance that with time it may spread around the body just like many other cancers. About 80% of cases of canine Cushing's disease are due to a pituitary tumour, whilst about 20% of cases are due to an adrenal tumour.
Cushing's tends to affect middle-aged to older dogs, and can cause a range of clinical signs. Dogs often drink excessively and therefore urinate a lot, are very hungry, may have a pot-belly, skin problems and symmetrical hair-loss, lethargy and panting. Not all these signs may be obvious, and there can also be other less common signs. Cushing's disease can cause diabetes in a few cases, but the diabetes is very difficult to manage until the cortisol levels in the blood are controlled.
Without treatment, high levels of cortisol in the bloodstream can cause heart disease (such as high blood pressure and heart failure), kidney problems, increased susceptibility to infections, pancreatitis and even blood clots.
Diagnosis
If your vet suspects Cushing's disease, routine blood tests will be done to look at a number of different substances in the blood. A urine sample will also be analysed and examined for any infections. If the routine blood tests support a possible Cushing's diagnosis, your dog will need an 'ACTH stimulation test' - for this your dog will need to be kept in the hospital for a few hours, but it just involves two more blood tests with an injection of a drug an hour before the second one.
An ultrasound scan (using sound-waves to make a picture of your dog's organs when a probe is placed on your dog's skin) may help to determine the size of the adrenal glands, and so help to decide whether the disease is caused by a tumour in the brain or in an adrenal gland. Sometimes this can be difficult to determine, so further blood tests may be necessary for confirmation. Your vet may want to do an X-ray of your dog too, to look for any enlargement of the adrenal glands and to check whether there are any tumours obvious elsewhere in the body.
Treatment
Treatment is based around oral tablets, usually 'Vetoryl' (containing a drug called trilostane), given once a day. To determine the correct dose of Vetoryl for your dog, several repeat ACTH-stimulation tests will be done, and your dog will need regular clinical assessments. It is important to measure your dog's water intake, and be aware of their appetite, activity and general well-being.
Blood tests are usually taken ten days after treatment has started, again 3 weeks later, and then every 12 weeks. It is best to take blood samples 4-6 hours after your dog has had his daily tablet. Your vet may want to be in contact with you frequently when treatment is first started, to monitor progress and make sure there are no adverse reactions to the tablets.
If the Cushing's disease is due to an adrenal tumour, surgery to remove the tumour may be an option. This will depend on the individual case and is a specialist operation, but is an option your vet and yourself may consider.
Dogs with pituitary tumours causing Cushing's disease have a mean life expectancy (with tablets) of in excess of two-and-a-half years, or four years for dogs which contract the disease at a younger age. Dogs with benign adrenaltumours have a mean life-span of three years, but the prognosis is poorer for dogs with malignant adrenal tumours that have already spread elsewhere in the body.
