Dog News

Cushing’s Disease

by Shawn Finch, DVM

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Cushing’s disease is rare in cats, uncommon in dogs and horses, common in ferrets, and also occurs in people.  Cushing’s disease is the common name for hyperadrenocortisism – a condition characterized by excess levels of cortisol produced by the adrenal glands.

I know what you may be thinking.  “Uncommon in dogs, and I don’t have a ferret, and those are some stupid long medical words…I hate when doctors do that.”  Wait, come back!  I think you may find this kind of interesting.  And if you do happen to have a dog with Cushing’s disease, the more you know, the better care you can provide.

The first thing any veterinary lecturer does when discussing Cushing’s disease is slap up an overhead or Power Point slide with one hundred huge medical terms and one hundred arrows. Vets don’t even like that!  We tune out too!  Even The 5-Minute Veterinary Consult book took three pages to explain the disease, when most others are covered in two.  (I LOVE that book, by the way.  It would be a good one if you are just interested in learning about different veterinary topics.)

Noodle the Poodle does not have Cushing's Disease, but some Poodles do!

Cushing’s Disease truly is complex, but it is such an interesting disease, and knowing about how the body works when things are out of balance in one specific way provides insight into – or at least well deserved awe for – how incredible the body is when everything is in balance.  So this will not be an all inclusive discussion on Cushing’s disease (though we can certainly discuss it further in the comments), but more of an overview so that you, as a dog lover, will know that much more about this wonderful species and their physiology.

First some explanations to make the medical words seem less stupid.  I am going to explain the ones I did not know until vet school, so forgive me if I over-explain, or worse, confuse you!

Adrenal glands – These are two little triangle shaped organs, one near each kidney.  The adrenal glands produce stress hormones, help balance electrolyes, oversee the production of sex hormones and manage the body’s “fight or flight” response.  If you’ve successfully managed a stressful day, thank your adrenal glands.  In fact, if you have survived the day, thank your adrenal glands.  I bet it will be the first time they have ever been thanked.

Pituitary Gland – This is a tiny bean-shaped organ near the center and “bottom” of the brain.  I imagine it as the little alien running the guy’s brain in the movie “Men in Black.”  It is much more exciting than that alien in Real Life, and even more powerful.  Among other things, it produces ACTH (adrenocorticotropic hormone) which signals the adrenal glands to produce cortisol.

Cortisol – This is the body’s main steroid hormone.  It supports life and helps manage the body’s stresses.

Which Dogs?

Little dogs, like Poodles and Schnauzers.  And sometimes big dogs.  Usually older dogs.  Cushing’s Disease has a genetic component, so that is why it tends to be more common in some breeds than others.  That most Cushing’s Disease sufferers are the little guys is just an unfortunate coincidence, I think.

How Things Become Unbalanced

Most cases of canine hyperadrenocortisism are caused by an adenoma (benign tumor) in the pituitary gland.  The pituitary gland secretes more ACTH than it should, which signals the adrenal glands to secrete more cortisol than they should.  The adrenal glands hypertrophy (get bigger) as they work to make and secrete so much more cortisol than normal.

Less common causes of hyperadrenocortisism are an adenocarcinoma (cancerous tumor) of the pituitary gland which starts the same chain reaction, or a benign or malignant adrenal gland tumor, which starts the pathway at the overproduction of cortisol.

A thankfully much less common cause of hyperadrenocortisism these days is long term steroid use.  We are much more stingy in our steroid use as a veterinary community than we used to be.  And even in dogs that have horrible allergies or life-threatening conditions in which they need steroids, we are better at balancing that and giving them at a low enough dose that Cushing’s disease does not occur.  It still happens, and sometimes at appropriate doses of steroids, but it is uncommon.

Lots and Lots of Cortisol

It can be quite a trick on our end to diagnose hyperadrenocortisism and to figure out whether the overproduction of cortisol is because of a pituitary or adrenal malfunction, but all your dog’s body knows is that all that cortisol is there, and it reacts, and that is where the signs of Cushing’s disease start showing up.  The excess cortisol affects all of the body’s systems, but especially the urinary system and skin.

Urinary Signs of Cushing’s Disease

Almost without fail, a dog with Cushing’s Disease will drink and urinate much more frequently and at a higher volume than normal, and may start having urinary accidents.  Any time this happens, it is worth a veterinary visit, as there are so many medical reasons a dog might drink and pee excessively!  Cushing’s Disease is just one on the long list.  In fact, we have a fun name for this phenomenon:  PU/PD.

PU/PD – polyuria (peeing a lot)/polydipsea (drinking a lot)

Other urinary signs are dilute urine (secondary to the PU/PD), and sometimes urinary tract infections.

Other Signs of Cushing’s Disease

Dogs with Cushing’s Disease often have a “pot-bellied” appearance.  They may be fat, but it is different…almost a bloated look.  The excess steroids weaken the connective tissue over time, so they are not able to hold in their tummies like normal, their liver may become enlarged and their fat stores become redistributed.

Their skin becomes thinner, their hair becomes sparser or disappears all together, they even have weaker ligaments.  Sometimes dogs with uncontrolled Cushing’s Disease will rupture cruciate ligaments (the ligaments behind their knee caps).  They are more prone to skin infections and sometimes develop hard calcium deposits in the skin called calcinotis cutis.

Cushing’s Disease makes dogs super hungry (polyphagia).  They are more prone to infections.  We do not tend to see mood swings, but I assume they occur based on the effects steroids can have on us.  If you have ever been on steroid medication, often many of the side effects we are warned of will happen to a dog with Cushing’s Disease.  Their own body is overdosing them on steroids.

Diagnosing Cushing’s Disease

Cushing’s Disease is put on a differential list (a list of possible causes of clinical signs) if a pet is showing signs consistant with Cushing’s Disease.  From there, screening blood tests are done and then tests to determine if the pet has Cushing’s Disease or not.  Finally, blood tests are done to determine if the Cushing’s Disease originates in the pituiary gland or an adrenal gland.  CT scans, ultrasound and exploratory surgery are often part of the diagnostic process as well.

Treating Cushing’s Disease

If an adrenal tumor is present and can be removed, it often is.  More often, the problem is the pituitary gland, and though pituitary tumors have been removed by veterinary surgeons in a handful of dogs, it is not routinely done.  Usually Cushing’s Disease is treated medically.

Oral medication is given to destroy PART of the layer of the adrenal glands that produces cortisol with the goal of bringing cortisol production back to normal.  The most common medication used is mitotane, though a few others are available, including Vetoryl (trilostane), and veterinary researchers are always looking for the next best treatment.  As you can probably guess, this is a tricky balancing act with very powerful medication.  Ideally, the pet can be maintained on a schedule that keeps the pet comfortable and adequately controls secondary issues.

Medically managed Cushing’s Disease is never cured, but dogs can do well with Cushing’s Disease for a very long time.  If secondary conditions (dermatitis, urinary tract infections and whatever else) are treated and cortisol levels can be brought back close to normal on a level of medication that does not cause side effects from the medication itself, the prognosis for a dog with Cushing’s disease is good.

Have you had or known a dog or other pet with Cushing’s Disease?  What have been your experiences with diagnosis, treatment, and prognosis?  Have your pets with Cushing’s Disease done well?  I sure hope so.

I hope for the rest of you that your only experience with this complex and intriguing disease is  this post, and that your pets have a long and healthy life filled with intricately and perfectly balanced levels of stress hormones!

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Here is a link to a Canine Cushing’s Disease Forum you may find helpful…

7/15/11  Thank you to Natalie for providing the link!  Her wonderful site K9Diabetes will be featured in Monday’s Canine Diabetes post (July 18, 2011), so stay tuned!