Cat Cushing's Disease

Introduction

Hyperadrenocorticism, commonly called "Cushing's Disease," is a disorder of excessive steroid secretion by the adrenal glands. In the vast majority of cases, this disease involves excess production of cortisol.

How Cushing's Disease Affects Cats

Hyperadrenocorticism is uncommon in cats. When it does occur, it has many of the clinical characteristics of Cushing's in dogs, but there are some very important differences.
Feline Cushing's is a disease of older, primarily mixed-breed cats of either gender. Unlike canine Cushing's, this disease in cats is strongly associated with diabetes mellitus. The most common initial clinical signs are increased water intake (polydipsia) and the resulting increase in urination (polyuria), together with increased appetite/eating (polyphasia). These signs are more likely caused by the diabetes than by the hyperadrenocorticism. Other signs during the early course of the disease are often subtle and nondiagnostic. Diabetes is typically diagnosed first. Cats with Cushing's will not respond normally to insulin therapy and, over time, will become progressively debilitated despite appropriate administration of potent insulin. They will lose weight relentlessly and develop severe cachexia (affected dogs tend to gain weight). Their skin will atrophy and become extremely fragile, thin, bruised, easily torn and ulcerated. Skin lesions are often noticed (or actually occur) during grooming or when the cat is handled for physical examination at the veterinary clinic. Other possible signs are weakness, lethargy, muscle atrophy, hair loss, diarrhea, vomiting, pendulous abdominal enlargement, poor wound healing and an overall unkempt appearance. Several, but not all, of these signs usually appear together.
Cushing's disease is very slowly progressive, and very few owners notice that there is anything "wrong" with their cat until the disease is advanced. Frequently, owners attribute the vague clinical signs to the normal effects of aging.

Causes & Prevention

Causes of Feline Cushing's Disease

Hyperadrenocorticism can be either pituitary-dependent (PDH) or adrenocortical-dependent (caused by an adrenal tumor, "ATH"). It is extremely rare for Cushing's in cats to be caused by iatrogenic administration of steroid drugs. Most affected cats have PDH; those with ATH have either benign adenomas or malignant adenocarcinomas, with roughly equal distribution. In cats with pituitary-dependent hyperadrenocorticism, excess secretion of adrenocorticotropic hormone (ACTH) from the pituitary gland stimulates the adrenal glands to produce excessive amounts of cortisol and causes the adrenal glands to enlarge (adrenal hypertrophy). Cats with functional adrenal tumors produce and secrete abnormally large amounts of cortisol autonomously.

Preventing Hyperadrenocorticism in Cats

There is no way to prevent hyperadrenocorticism in cats. It occurs for reasons as yet unknown.

Special Notes

Treatment of Cushing's disease requires reducing or preventing the excessive production of steroids. Surgical excision of affected adrenal glands is possible and usually quite successful. A number of drugs also are available to either inactivate the adrenal glands or to otherwise regulate and normalize the amount of steroid production.
The prognosis for cats with hyperadrenocorticism is guarded to poor. While surgical removal of affected adrenal glands is possible and has the potential to be quite successful, it requires prior correction of the cat's debilitated condition, a very skilled surgeon and owner commitment to medical management of the prospective steroid deficiency.

Diagnosis & Tests

Feline Cushing's, also called hyperadrenocorticism or HAC, is a disorder of excessive cortisol secretion by the cat's adrenal glands. Cushing's is uncommon in cats, although it is common in dogs. When it does occur in cats, it typically is caused by bilateral enlargement of the adrenal glands caused by pituitary hyperplasia or tumor. Regardless of the underlying cause, feline Cushing's is usually associated with diabetes mellitus.

Diagnosing Cushing's Disease in Cats

Any cat that your veterinarian suspects of having hyperadrenocorticism should have an initial database of a complete blood count (CBC), a serum biochemistry profile and a urinalysis with a bacterial culture. Other fairly routine diagnostic tests include abdominal and thoracic (chest) radiographs or ultrasound, and blood pressure assessment.
Advanced testing to confirm a diagnosis of Cushing's disease includes a urine cortisol:creatinine ratio analysis, a low-dose dexamethasone suppression blood test, a high-dose dexamethasone suppression blood test, an ACTH stimulation blood test, and/or an assessment of endogenous blood ACTH concentrations. Magnetic resonance imaging (MRI) and computed tomography (CT) are also available to aid in diagnosis.
One of the simplest and least expensive of these tests is the urine cortisol:creatinine ratio test. Normally, the owner is asked to catch the first morning's urine at home and bring it to their veterinarian for measurement of cortisol and creatinine levels, although this can be quite difficult with cats. A normal test result pretty much rules out the diagnosis of Cushing's. However, abnormal test results (called "false positives") are common in many cats that do not have Cushing's disease, making further diagnostic tests necessary.
The high and low dose dexamethasone and ACTH blood tests, done together or separately, can provide a conclusive diagnosis of Cushing's disease. These tests involve taking an initial blood sample, then giving the cat an injection of either dexamethasone or ACTH, then taking subsequent blood samples at appropriate intervals. All of the blood samples are sent to a laboratory for analysis. Your veterinarian will decide which test is best in a given case.
Cushing's disease symptoms in cats can often mimic other diseases, and an accurate Cushing's diagnosis involves a lot of detective work. Initial blood and urinalysis tests will help to uncover any other possible causes of the symptoms such as diabetes or hypothyroidism, and the results of these initial tests will show if Cushing's disease is indeed a possible diagnosis.
The ACTH stimulation test is very expensive and available only in some areas. This test will only identify Cushing's disease but not the type of Cushing's. Only the dexamethasone suppression tests will help to diagnose the type of Cushing's disease that is present. Your veterinarian will decide which test is best.
An abdominal ultrasound is sometimes used to aid in Cushing's diagnosis as well. The ultrasound will show if one, or both, of the adrenal glands is affected by Cushing's, and the ultrasound will also show if any other organs have been affected by the disease.

Treatment Options

Cushing's disease, otherwise known as hyperadrenocorticism, is a disorder of excessive cortisol secretion by the adrenal glands. It is a rare disease that usually is only diagnosed in cats over 7 years of age. The disease can be caused by the administration of excessive steroid medications or by tumors on the adrenal or pituitary glands of affected cats. The treatment options for cats with Cushing's are limited, and in many cases the treatment protocols are quite risky. Unfortunately, once clinical signs of Cushing's are present in cats, the disease has already progressed to an advanced stage.

Treating Cushing's Disease in Cats

Feline Cushing's Disease (FCD) is extremely debilitating to affected animals. Cats tend to have better treatment options than do dogs. Affected cats should have medical treatment prior to surgery to prevent complications from fragile skin, infections and bruising. Since this condition often has been caused by the administration of steroid medications, the most common treatment is to slowly wean the cat off of the medications. An abrupt end to steroid medications can cause other medical disorders, and so the medications must slowly be reduced under the supervision of a veterinarian.

Medical Therapy

There are a number of medications available to treat Cushing's disease in cats, whether the disorder is caused by pituitary or adrenal tumors. Only some cats with Cushing's disease respond positively to these medical treatments, and the medications come with their own side effects.

Surgical options

If oral or injectible medications do not manage the effects of Cushing's disease, surgical removal of the adrenal gland is the last available option. This surgery is extremely risky, and only about one-half of all patients survive. If your cat has been diagnosed with Cushing's disease, it is important to have an honest discussion with your veterinarian About the treatment options and possible outcomes you can expect. You may also want to ask for a referral to a veterinary specialist, as many veterinarians do not have experience treating Cushing's disease in cats.