Because the signs of feline Cushing’s disease can mimic a number of other diseases, getting an accurate diagnosis involves a lot of detective work. The veterinarian usually will be presented with a cat that is lethargic, drinking and urinating more than usual and developing a potbelly and a poor hair coat. These are very non-specific signs that can be caused by any number of disorders. The veterinarian will take a thorough history from the cat’s owner and conduct a complete physical examination. She probably will take blood and urine samples and submit them to a laboratory for detailed evaluation. The results of those tests may reveal the cause of the cat’s symptoms, which may be diabetes mellitus or hypothyroidism. However, the results of those tests can also indicate whether Cushing’s disease is or is not a probable diagnosis.
Any cat that a veterinarian suspects of having Cushing’s disease will have an initial database of a complete blood count (CBC), a serum biochemistry profile and a urinalysis with bacterial culture. Other fairly routine diagnostic tests include abdominal and thoracic (chest) radiographs (X-rays), ultrasonographs and blood pressure assessment. Advanced testing requires 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 levels. Magnetic resonance imaging (MRI) and computed tomography (CT scans) are also available to aid in the diagnosis of Cushing’s in cats.
One of the simplest and least expensive diagnostic tools is the urine cortisol:creatinine ratio test. The owner must catch the cat’s urine first thing in the morning and bring it to the veterinarian for measurement of cortisol and creatinine levels. A normal test result basically rules out a diagnosis of Cushing’s. However, abnormal results (“false positives”) are common in cats that don’t have Cushing’s, which makes further 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, giving the cat an injection of either dexamethasone or ACTH, and then taking subsequent blood samples at specific intervals. The ACTH stimulation test is expensive and only available at some clinics. It will identify Cushing’s disease but will not identify the type or cause of the condition. Only the dexamethasone suppression test will reveal the type or cause of the cat’s Cushing’s disease. The cat’s veterinarian will decide which test is most appropriate in any given case.
Abdominal ultrasounds are sometimes used to help diagnose Cushing’s disease in cats. The ultrasound images will show if one, or both, of the cat’s adrenal glands are abnormal and can also reveal other abdominal abnormalities that may have been caused by the disease