Diagnosing Canine Cushing's Disease with an ACTH Stimulation Test

Canine Cushing’s disease is a condition where too much cortisol is in the bloodstream. The complex system of pituitary gland, hypothalamus and hormone secretions is broken, making the dog’s body unable to regulate the cortisol production. The elevated cortisol levels in turn have an impact on various body systems including nervous system, cardiovascular system, skeletal muscles, blood sugar levels, fat metabolism, kidney function and immune response. Once diagnosed, Cushing’s disease can be treated, allowing the dog to live a more comfortable life and avoiding the secondary problems caused by the disease. While no single test can properly diagnose Cushing’s disease, the ACTH stimulation test, used in tandem with other diagnostic results, can pinpoint the diagnosis.

ACTH Stimulation Test

The ACTH stimulation test is conducted by comparing baseline blood work against blood work taken 1 to 2 hours after an injection of the ACTH hormone. ACTH is the hormone that is naturally produced in the pituitary gland and triggers the release of cortisol from the adrenals into the dog’s system. If the test results show an extremely elevated level of cortisol in the bloodstream, it is likely the dog has Cushing’s disease. The ACTH stimulation test is often done in conjunction with a low dose dexamethasone suppression test in order to confirm the diagnosis of Cushing’s disease.

Neither of these tests can differentiate between the different causes of Cushing’s disease. In order to do this, a high dose dexamethasone suppression test must be conducted. Baseline blood work is compared to blood work at 4 and 8 hours after the dog has been given a high dose of dexamethasone. The test results will determine the cause of the Cushing’s disease and allow the veterinarian to prescribe the appropriate treatment.

Treatment for Cushing’s Disease

Because most dogs diagnosed with Cushing’s disease are elderly and already being treated for other medical conditions, treatment can be complicated. For Cushing’s caused by adrenal tumors, surgical removal of benign tumors can cure the disease. Malignant adrenal tumors often go unrecognized until the tumor has already attached itself to the liver or lungs. In these cases, non-surgical treatment is often the route taken.

Medicinal treatment for pituitary dependent or for inoperable adrenal-based Cushing’s disease is done, not to cure the disease, but to make the dog’s quality of life more comfortable. Your veterinarian will choose the drugs based upon your dog’s condition, the type of Cushing’s present and other medications your dog may be on.

Iatrogenic Cushing’s is caused by medications that cause overproduction of corticosteroids. Gradual withdrawal of the offending medication will allow the dog’s body to fully recover and return to a non-Cushing’s state.

The ACTH stimulation test allows your veterinarian to determine whether or not your dog’s body is producing excessive amounts of cortisol and creating a toxic situation that can affect a variety of his body’s systems. Once the initial diagnosis is confirmed by additional tests, and the cause of the Cushing’s disease identified, treatment can begin, allowing your dog to live his life more comfortably.