CUSHING’S SYNDROME

            Just about a year ago, my oldest golden was diagnosed with Cushing’s Syndrome.  He would turn 9 on July 2nd.  When the vet first uttered the words of diagnosis, I knew I had heard of the disease but like other diseases or illnesses that hadn’t yet “invaded my personal space,”  I wasn’t well versed with the disease nor its symptoms.  One of the first things I remember being told and then reading over and over and over….was that the average life span once diagnosed was “about 2 years”.  Whoa!  My guy was only going to be 9 and prior to this time, he was a very healthy dog.  I was not prepared, nor ready to have him only have 2 years left!!  Not if I could help it!!  Thus, my journey into learning about “Cushing’s Syndrome” and how to reserve the damage and control the disease began.

Cushing’s Syndrome?  Just what exactly is it?  The medical term for Cushing’s Syndrome is HYPERADRENOCORTICISM.  After trying to pronounce that word a few times, I could see why they gave the disease another name!  Unfortunately, whether you call it by it’s scientific name or for the doctor who discovered the disease, it is a very common condition that does appear in older dogs.  Many owners will sometimes mistake the symptoms for the simple “aging process” we inevitably see in our elderly canine companions.  Sadly, owners will often times consider early euthanasia when the proper diagnosis isn’t made. Yet, once diagnosed, the disease is very treatable!!  Trust me, my boy is “LIVING” proof!

So, once I got over the shock that my boy had a disease that wasn’t going to go away, I started doing my research into disease/syndrome.   I soon learned that a healthy dog, like humans, has a pituitary gland located at the base of the brain.  This gland produces a hormone that is called adrenocorticotrophic, more commonly referred to as ACTH.  ACTH is released into the bloodstream.  It stimulates the body’s two adrenal glands that are located near the kidneys to release and secrete glucocorticoid hormones.  The glucocorticoid hormones are called cortisol.  Cortisol is a cortisone-like hormone and is the hormone that helps the body respond to stress.  It also regulates and has a vast affect on a wide variety of bodily functions, some of which include maintaining blood sugar levels, fat metabolism, kidney function, cardiovascular system, nervous system, skeletal muscles and the overall immune responses in the dog.  I learned that when a dog gets stressed,  his ACTH/Cortisol secretion increases.  It will also increase when an infection is present, he is in pain, has gone through surgery and during cold temperatures.  When the blood cortisol levels are high enough, the pituitary will stop secreting the ACTH hormone.  Should the blood levels get low, the pituitary once again secretes the necessary ACTH.  The adrenal glands, in turn, kick in and do their part by secreting the glucocorticoid hormone and vice versa.  When all is well and working correctly, all the glands work in harmony and a mildly fluctuating balance is maintained. 

When a dog is diagnosed with Cushing’s Syndrome,  it usually means one of three things has gone awry.  There is either a tumor on the pituitary gland, a tumor on the adrenal gland or what is known as “veterinary induced” Cushing’s. Whatever the “reason”, the result is a constant, excessive level of blood cortisol in the dog’s system.  The inter-twined workings of the pituitary gland and adrenal gland have ceased to regulate the blood cortisol level.  90% of all Cushing’s cases are pituitary dependent, with the remaining 10% being adrenal gland based.  The veterinary induced Cushing’s is called Iatrogenic Cushing's (non-spontaneous) and occurs as the result of over administration of corticosteroids such as prednisone (one example).

What symptoms should warrant a trip to the vet?

·         Increased/excessive drinking (polydipsia or PD)

·         Increased/excessive urination (polyuria or PU)

·         Increased/excessive appetite (polyphagia)

·         enlarged, distended abdomen

·         muscle weakness (most commonly in the back legs)

·         thinning hair (alopecia--usually evenly distributed) and lack of new hair growth

·         thinning skin

·         "skull-like" appearance of head

·         hyperpigmentation of skin

·         calcified skin bumps

·         obesity

·         chronic or frequent infections (most notably pancreatitis, urinary tract infections, strep throat, and staph infections)

In addition, behavioral symptoms may include:

·         lethargy/decreased activity

·         increased panting

·         seeking out of cool sleeping surfaces (bathroom tiles, etc.)

·         disturbance of the sleep/wake pattern (increased sleeping during the day, restlessness at night)

·         decreased interaction with owners

My boy had just a few of the symptoms, so keep in mind that your dog doesn’t have to have every symptom!  When looking back over the 6 months prior to his diagnosis, two of the most “obvious” but not recognized symptoms were “increased panting” and the “skull-like” appearance of head.  Boomer was diagnosed in June and I remember during the winter months, while working on my computer, Boomer would be lying at my feet and “panting”.  I would reach down and pat him on head and tell him to “calm himself”….and being the ever-good boy, he would stop for a while but then start back up.  I thought it odd, him panting in the dead of winter…but never thought anything was “wrong”.  He seemed perfectly fine in all other aspects.  Another sign I didn’t get too concerned about was the skull-like appearance of his head.  I put that one down to his aging.  How wrong I was!!  What finally got the diagnostic process in gear was that during the month of May, he had a bout of diarrhea.  Due to his senior age, I took him in to the vet and asked for a complete blood chemistry.  The results of that blood chemistry is what tipped the vet off to Cushing’s and further testing commenced. 

The diagnosis of Cushing’s Syndrome is not always an easy one and a thorough approach is needed.  One of the first things a veterinarian may do is run a complete blood chemistry profile and possibly a urinanalysis.  With the blood chemistry profile, the vet is looking for elevated white blood cell counts (especially neutrophils), elevated liver enzymes (particularly alkaline phosphatase), and elevated cholesterol levels in conjunction with clinical symptoms.  Elevated levels suggest that Cushing's may be present and indicate a need for further, more specific testing such as skin biopsies, ultrasounds and radiographs..  A urine-creatinine test may also be run, although the results of that test does not “confirm” the disease, it can only rule it out.  About 80 % of dogs that don’t have Cushing’s will also have an increased level and will need further testing; however, if the test comes back normal, then it is unlikely that Cushing’s is present.  This test is useful however, as a screening tool, when the differential diagnosis does not put Cushing’s at the top of the list.

After the initial blood tests, vets may likely want to perform what is known as an ACTH Stim Test for initial diagnosis and then most likely, either a Low Dose Dexamethasone Suppression Test (LDDS Test) to further help distinguish between Pituitary Dependent Cushings or Adrenal .  Both tests require blood being drawn to measure the “baseline” (or pre-test) blood cortisol level. 

In the ACTH Stim Test, the dog is given an injection of ACTH.  After the injection and a period of 2 hours another blood sample is drawn.   If the second test of cortisol is much higher than the first, it is suggestive of Cushing’s  80- 95% of the time.  It does not necessarily tell us if it is PD (pituitary dependent) or AT (Adrenal Tumor) because this exaggerated response will occur in 85% of PD Cushing’s and about 50% of those with AT Cushing’s.

In the Low Dose Dexamethasone Suppression Test, an injection of Dexamethasone is given and cortisol levels are measured at 4 hours and 8 hours after injection.  In this test the vet will look at the 8 hour sample first.  The cortisol levels in a non-Cushing’s dog should be below the baseline level taken pre injection.  If it is not, then a diagnosis of PD or AT Cushing’s is made or there is a false positive result.  If the 4 or 8 hour cortisol test result is less than 50% of the normal resting cortisol, then a diagnosis of PD Cushing’s is made or a false positive is made. If the 4 hour or 8 hour cortisol test result is greater than 50% of the normal resting cortisol, then a diagnosis of Cushing’s is made or there is a false positive.  In this last scenario it cannot be determined if the Cushing’s is PPD or AT.  False positives can be had in both tests, however the LDDS test will catch most cases. 

A High Dose Dexamethasone Suppression Test (HDDS Test) is also used, but not generally as a screening tool.  This test is usually done on a dog that already has been diagnosed with Cushing’s and where you want to be certain the Cushing’s is not caused by the occasional adrenal tumor.

With Boomer’s diagnosis, we ran the gamut of tests.  As I mentioned above, first we did the Blood Chemistry Profile, then a urine-creatinine test, the ACTH Stim Test and finally, to determine between PD or AT Cushings, the LDDS Test.  Boomer’s numbers fell within the numbers to confidently diagnosis him with PD Cushings.   It seemed like waiting for the final diagnosis took forever, but I was still at that point of reading all I could about the disease and the various treatments offered, along with the “treatment of choice” used by most U.S.   veterinarians.

Next month I will discuss these various “treatments”, the one I opted to go with and Boomer’s state of health…one-year post diagnosis!  Until then, if you want to learn more about Cushing’s, below is a great web page devoted to the disease and which was my reference for this article. 

References: http://www.lbah.com/Canine/cushings.htm

 Return to current medical article