Hyperadrenocorticism (Cushing's syndrome) is a disorder of the adrenal glands that is most often due to a tumor of the pituitary gland.
In some cases the disease originates in the adrenal glands. Hyperadrenocorticism is relatively frequent in dogs and is rare in cats. Treatment of the disease offers very good chances of success, in either dogs or cats. In order to better understand the disease and help owners of animals affected by hyperadrenocorticism, this web-page contains the most frequently asked questions. Every question is followed by a brief answer. If the reader wishes to receive more details, Dr. Eric Zini, responsible of the Internal Medicine department, can be contacted at the following email address: firstname.lastname@example.org
What is hyperadrenocorticism (Cushing's syndrome)?
Hyperadrenocorticism (Cushing's syndrome) is a disorder that causes an increased synthesis of glucocorticoids. Glucocorticoids are naturally produced by the organism but in dogs and cats with the disease they are produced in excess. The disease arises from prolonged exposure to elevated concentrations of glucocorticoids. Because glucocorticoids affect several organs and therefore clinical signs are different, the disease is often referred to as syndrome (Cushing's syndrome).
What are glucocorticoids?
Glucocorticoids are a group of steroid hormones produced by the adrenal glands. Cortisone belongs to this group. The adrenals are small glands located nearby the kidneys. Glucocorticoids have different effects: they are important to counteract stressful situations, they increase blood glucose concentrations (glycemia), they modify bone and muscular metabolism, and they modulate the response of the organism to different hormones. Among glucocorticoids, cortisol is the most important hormone.
What are the causes of hyperadrenocorticism (Cushing's syndrome)?
Hyperadrenocorticism (Cushing's syndrome) can be caused by a tumor of the adrenal gland that synthesizes glucocorticoids in excess, or can be caused by tumors arising in the pituitary gland. The pituitary is a gland located within the brain that controls the adrenal glands. Stimulation of the adrenal glands by the pituitary tumor leads to excessive glucocorticoids production.
In less frequent cases, hyperadrenocorticism (Cushing's syndrome) can be due to administration of elevated doses, or for prolonged periods, of steroideal drugs (corticosteroids). This condition is referred to as "iatrogenic" hyperadrenocorticism. Tapering or discontinuation of steroideal drugs (corticosteroids) allows recovery from "iatrogenic" hyperadrenocorticism.
When is hyperadrenocorticism (Cushing's syndrome) suspected?
In dogs with hyperadrenocorticism (Cushing's syndrome) typical clinical signs are increased appetite (polyphagia), increased thirst (polydipsia), increased urine production (polyuria), hair loss (alopecia) with skin hyperpigmentation, increased size of the abdomen (pot belly) and decreased muscular masses. Skin lesions in dogs with hyperadrenocorticism (Cushing's syndrome) often are clinically indistinguishable from those associated with hypothyroidism and, in different cases, only the specialist's expertise can help differentiating the two diseases.
In addition, in cats with hyperadrenocorticism (Cushing's syndrome) skin often becomes very fragile and can easily tear, with wounds that are difficult to heal.
The above clinical signs, although not specific, can lead to suspect hyperadrenocorticism (Cushing's syndrome) in dogs and in cats.
How is hyperadrenocorticism (Cushing's syndrome) diagnosed?
Diagnosis of hyperadrenocorticism (Cushing's syndrome) in dogs and cats is achieved by combining clinical signs with abnormalities observed at blood work, urinalysis and diagnostic imaging (abdominal ultrasonography or CT scan), and with endocrine tests.
Common endocrine tests are the low-dose dexamethasone suppression test, the ACTH stimulation test and the cortisol to creatinine urinary ratio. Less frequent tests are the high-dose dexamethasone suppression test and the measurement of endogenous ACTH. The listed tests differ for their capacity to identify (sensitive test) or exclude (specific test) the disease and are characterized by different execution modalities and times, in dogs and in cats. Task of the veterinarian is to select the most appropriate test or tests in order to rule-in or rule-out the diagnosis of hyperadrenocorticism (Cushing's syndrome).
How is hyperadrenocorticism (Cushing's syndrome) treated?
Once the diagnosis of hyperadrenocorticism (Cushing's syndrome) has been confirmed, treatment depends on its cause. Surgery solves the disease in case of pituitary gland or adrenal gland tumors in either dogs or cats. Treatment is achieved by removing the tumor by means of hypophysectomy, for pituitary gland neoplasia, or adrenalectomy, for adrenal gland neoplasia. Both surgeries are very complex and should be performed by veterinary surgeons with skill in neurosurgery, microsurgery and vascular surgery.
If surgery cannot be performed, medical treatment of hyperadrenocorticism (Cushing's syndrome) is the choice. Medical treatment relies on administration of specific drugs that reduce the production of glucocorticoids. The most used drug in dogs and cats is trilostane. Trilostane should be administered with food in order to be fully efficacious. Medical treatment must be continued lifelong. Monitoring of medical treatment by the veterinarian is necessary to confirm adequate control of the disease and to avoid overdosing. If the resulting concentration of glucocorticoids is too low, dogs and cats can develop weakness, nausea and vomiting, electrolyte imbalances and, in severe cases, shock.
Can hyperadrenocorticism (Cushing's syndrome) lead to death?
Hyperadrenocorticism (Cushing's syndrome) is an endocrine disease that is caused by a tumor. Pituitary gland tumors are usually benign in dogs and cats. However, they may grow and cause brain compression and, in some cases, they may cause death. Tumors of the adrenal glands can be either benign (adenoma) or malignant (adenocarcinoma). In the latter case in dogs, metastases are identified in approximately 50% of cases and prognosis is poor.
In addition, hyperadrenocorticism (Cushing's syndrome), both in the spontaneous form and in that caused by the administration of steroideal drugs ("iatrogenic" hyperadrenocorticism), is a disease that leads to severe complications if uncontrolled. Among complications the following are most important: thromboembolism, diabetes and ketoacidosis, hypertension and bacterial or fungal infection. Dogs and cats can die because of the listed complications.
Can hyperadrenocorticism (Cushing's syndrome) be cured?
Cure from hyperadrenocorticism (Cushing's syndrome) is possible if the tumor is surgically excisable and if metastases are absent. Cure is also possible if hyperadrenocorticism is caused by the administration of steroideal drugs ("iatrogenic" hyperadrenocorticism), simply by tapering or discontinuing treatment.