The Adrenal Diseases: Cushing's and Addison's
Gaston Phoebus and Hunters, (c.1500),
Gaston Phoebus, Book of the Hunt
Gaston Phoebus, Count of Foix and author of the book, surrounded by hunters.
© The Bibliothèque Nationale de France; FR 616, fol. 13
(hyperadrenocorticism) is the more common of the adrenal
disturbances. It is seen in middle aged to older dogs. The adrenals
are pea-sized glands adjacent to the kidneys whose normal function
is to produce the body's steroids. The overactive adrenals of
Cushing dogs produce an overabundance of steroids. The actual defect
in most cases is a benign pituitary (brain) tumor that secretes
excessive amounts of adrenal stimulating hormone (ACTH), sending the
adrenals into high gear. Only 15% of Cushing dogs have a secretory
tumor of the adrenal gland itself.
Cushing dogs act (and can look) just
like dogs who have been given too much prednisone. They drink a lot,
pee a lot, are always hungry, gain weight, and may pant excessively.
Over time, the bad effect of "oversteroiding" causes the hair to
thin and the muscles to weaken, producing the classic poochy-bellied
"barrel on four pins" appearance. Cushing dogs may rupture a
cruciate (knee) ligament for no apparent reason. Just as might be
expected for a dog on steroids, they don't heal well and are subject
to pressure sores. They are also more susceptible to infections,
Screening tests such as ALKP, urine
cortisol:creatinine, and ACTH stimulation help rule in or out
Cushing's. "Definitive diagnosis" is by dexamethasone suppression
test. "Definitive diagnosis" because dogs can be misdiagnosed on the
basis of lab tests alone. Cushing suspects must show clinical signs.
Though not every dog will show every sign, Cushing dogs uniformly
drink and pee a lot. A practical observation is that they cannot go
overnite without peeing. The confounding element in lab tests is
that any sickness or stress can elevate cortisol levels, resulting
in a "Cushingoid" diagnosis. Further, tests must wait until any form
of medication with steroid ingredients - even ear drops or skin
cream - is out of the dog's
There are two treatment options for
Cushing's. Lysodren (mitotane) pills are a "sure thing" because they
destroy the adrenal glands, thus stopping the oversupply of
steroids. Because the body needs some steroid to function properly,
Lysodren treatment must be fine-tuned and monitored regularly by
ACTH stimulation testing. Most dogs will wind up on a twice weekly
The other treatment option is daily
Anipryl (selegiline) pills, which work by counteracting the steroid
as it's made. Anipryl has a lower success rate, but is reasonable to
try first if the dog is still in good shape. There is no test to
monitor Anipryl response - dose adjustments are made on the basis of
the owner's observation of clinical signs. Though Cushing dogs
cannot always be made "perfect," there is no reason that a
well-controlled Cushing dog cannot live a normal life and lifespan.
Addison's disease is essentially the
opposite of Cushing's - hypoadrenocorticism. Addison dogs have
underactive adrenal glands, most often the product of
immune-mediated adrenal destruction which can occur younger and is
much rarer than Cushing's. In addition to destruction of the
glucocorticoid ("steroid") layer of the adrenal gland, Addison's may
also destroy the mineralocorticoid layer of the adrenal gland, which
regulates sodium and potassium conservation.
As might be expected, these dogs
without enough steroid in their body may be dull and thinnish, to
the point of "poor doer." Others
appear outwardly normal. Bouts of gastrointestinal upset are common
- signs tend to wax and wane. Because of these nonspecific signs,
Addison's is known as the "great imitator" and it's not uncommon for
clients to be on their second and third opinions before a diagnosis
is made. To catch these, one must always keep Addison's in the back
of their mind as a possibility for ADR ("ain't doin' right") cases.
Addisonians often respond to symptomatic treatment (IV fluids and/or
steroids), thus some dogs "recover" and go on undiagnosed until they
collapse from extreme electrolyte imbalance - the classic
"Addisonian crisis." High potassium and low sodium are the usual
tipoff on bloodwork - from there the diagnosis is straightforward
with an ACTH stimulation test. There are, however, "trick cases"
that may only have destruction of the glucocorticoid layer,
and bloodwork on these dogs will not
necessarily show changes in sodium and potassium
Treatment consists of replacing the missing steroids. A small daily prednisone dose takes care of the glucocorticoid requirement. Mineralocorticoids are replaced with either twice daily Florinef (fludrocortisone) pills or monthly Percorten (desoxycorticosterone pivalate) injections. As long as you catch an Addisonian before he dies in a crisis, he can live normally on medication. A small percentage of Addisonians go on to develop immune destruction of other organs.
Copyright 2010 GreytHealth.com. All rights reserved.
Website by WagWorks