Introduction

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.