Issue Description Cushing's syndrome is a condition in which
there is an excess of cortisol (cortisone). Cushing can be caused by
drugs (e.g. prednisone, depo-medrol, dexamethasone, betamethasone)
often prescribed for the treatment of many diseases; this syndrome is
known as iatrogenic Cushing's syndrome. It can also be caused by an
excess of the body's own cortisol, caused by a pituitary tumor or
adrenal tumor. Other Names Hyperadrenocorticism, Hypercorticism
Latrogenic Cushing's syndrome is caused by
administration of drugs that suppress the body's own cortisol
production. Clinical signs and complications are similar to the
naturally occuring disease. The dog can become dependent upon the
drugs with chronic use, and abrupt withdrawal can lead to signs
related to lack of cortisol, such as lethargy, depression, vomiting,
and diarrhea. For these reasons, chronic steroid use is not
recommended except in cases of life-threatening immune-mediated
disease or chemotherapy protocols.
Pituitary dependent Cushing's disease is caused by a functional
pituitary tumor that stimulates the adrenal glands to produce excess
cortisol. The tumor is usually microscopic and benign. Sometimes the
tumor can be large enough to cause pressure on the nerves to the eyes
and the part of the brain called the hypothalamus, causing behavior
changes, lack of appetite, and blindness, in addition to the other
signs of Cushing's syndrome. Pituitary-dependent Cushing's disease
makes up about 85% of spontaneous Cushing's disease cases.
Adrenal tumors can be benign, known as adenomas, or malignant,
known as carcinomas. They produce cortisol independent of the normal
regulatory mechanisms of the body. This is the cause of approx. 15% of
occurrences of Cushings.
Symptoms Symptoms of Cushing's disease can be vague and
varied and tend to appear gradually and progressively. It is thus easy
to mistake Cushing's disease for normal aging. Additionally, many of
the clinical symptoms are not unique to Cushing's and could reflect a
number of other health concerns.
The most common symptoms include:
increased/excessive water consumption (polydipsia)
increased/excessive urination (polyuria)
urinary accidents in previously housetrained dogs
increased/excessive appetite (polyphagia)
appearance of food stealing/guarding, begging, trash dumping, etc.
sagging, bloated, pot-bellied appearance
weight gain or its appearance, due to fat redistribution
loss of muscle mass, giving the appearance of weight loss
bony, skull-like appearance of head
exercise intolerance, lethargy, general or hind-leg weakness
new reluctance to jump on furniture or people
excess panting, seeking cool surfaces to rest on
symmetrically thinning hair or baldness (alopecia) on torso
hard, calcified lumps in the skin (calcinosis cutis)
susceptibility to infections (especially skin and urinary)
diabetes, pancreatitis, seizures
It is generally either the increased water intake and urination or the
coat changes which prompt an owner to have their dog evaluated by the
veterinarian, as these dogs don't appear suddenly and dramatically
ill. It is estimated that 80-85% of Cushingoid dogs have increased
water consumption, drinking from 2-10 times normal amounts (normal is
considered 1 ounce of water drunk per pound of body weight per day).
85-100% of Cushingoid dogs have skin and coat changes. 80-90% of
Cushingoid dogs have an increased appetite, and 90%-95% have a
pot-bellied appearance. Considered a disease of middle and old age,
dogs typically display symptoms at some point after 6 or 7 years of
age. It is estimated that most dogs display some symptom(s) of the
disease for one to six years before Cushing's is actually suspected
and diagnosed. Certainly it is harder to ignore a dog that urinates
throughout the house or a dog who is balding than it is to overlook an
older dog who is gradually slowing down on walks.
indirect symptoms to consider are the disappearance of previous
inflammatory conditions. Dogs with chronic allergies or arthritis may
appear considerably better when they develop Cushing's, due to the
heavy doses of cortisone they are giving themselves.
Diagnosis Cushing's disease can present with a variety of
symptoms and may also be involved with several different disease
processes. Therefore, it is recommended that any dog suspected of
having Cushing's disease should have a complete blood count (CBC),
blood chemistry panel, and urinalysis performed as a routine part of
the evaluation. Common abnormalities in these tests include increases
in alkaline phosphatase, and ALT (liver enzymes), increased
cholesterol, decreased BUN (a kidney function test), and dilute urine
(low specific gravity).
There are several different tests
that can be performed to get a definitive diagnosis of Cushing's
disease. Many times the veterinarian may perform more than one test to
help confirm the diagnosis or to determine which form of the disease
is present. A diagnosis of Cushing's disease, however, should never be
made on the basis of laboratory tests alone. The dog needs to be
showing symptoms of the disease, and have a medical history consistent
with the diagnosis.
The three most common "screening" tests
are the urine cortisol:creatinine ratio, the low dose dexamethasone
suppression test, and ultrasound.
Treatment Treatment depends on the type of Cushing's
disease, as well as on the overall health of the canine patient. As
many dogs with Cushing's are elderly and may have concurrent health
problems, treatment can be complicated. The comfort of the patient
should be the ultimate goal. In a dog with severe arthritis, for
example, it may be more humane to allow him to remain Cushingoid than
to treat the disorder. In general, surgery may be indicated for
adrenal tumors. Chemotherapy in the form of Lysodren or Ketaconazole
may be used to treat pituitary-dependent or adrenal-based Cushing's.
And Anipryl may be tried to combat pituitary-dependent Cushing's.
Treatment is best viewed as a means to improve quality of life, rather
than increase lifespan.
If Cushing's disease is caused by
an adrenal tumor, the logical approach is to surgically remove the
tumor and the affected adrenal gland. These tumors tend not to recur
on the remaining adrenal gland. In theory, this can cure adrenal-based
Cushing's disease, and prognosis is very good for dogs with benign
adrenal tumors. Dogs may be treated with ketoconazole prior to surgery
to try to minimize the symptoms of Cushing's disease, as one
significant symptom of Cushing's is delayed wound healing. There are
high risks associated with adrenalectomies, and given that patients
are often elderly dogs, this may deter an owner from pursuing this
treatment route. 50% of adrenal tumors are malignant and may have
already metastasized to liver or lungs by the time they are
discovered. Most owners opt for non-surgical treatment.
Pituitary tumors are not removed surgically in veterinary medicine.
These tumors tend to be very small and slow-growing and cause little
or no damage on their own, aside from overstimulating the adrenal
glands. With these canine patients, the symptoms themselves are
treated and not the root cause.
Pituitary macroadenomas may
be treated with radiation in an attempt to shrink them and thus
relieve the neurological symptoms caused by their presence and the
pressure they place on brain tissue. Radiation involves thousands of
dollars and repeated anesthesia, either of which may be difficult to
justify with an elderly patient. Once the neurological symptoms abate,
the dog would then be treated for hyperadrenocorticism itself.
Prognosis Dogs usually respond very well to therapy and
are able to lead normal lives. Relapses are quite common with
pituitary-dependent Cushing's syndrome, and occur in about half of
dogs with Cushings. This generally requires a change in the
maintenance dose or re-induction therapy. Good owner observation and
communication with the veterinarian are the most important factors
that influence the success of treatment. Surgery will cure many benign
adrenal tumors and small carcinomas. If there are no post-operative
complications, there can be prolonged survival even with invasive
tumors or with metastatic disease.