Hyperadrenocorticism is one of the most common hormonal disorders in middle-aged to older dogs; it is rare in cats.

The disorder, also known as Cushing's Disease, is caused by the harmful effects of high cortisol concentrations on many organs in the body.

Cortisol is a hormone secreted by the adrenal glands, which are located near the kidneys.

It is produced specifically by the adrenal cortex that is the outer layer of the adrenal gland. The functions of cortisol include roles in the regulation of blood pressure and cardiovascular function as well as regulation of the body's use of proteins, carbohydrates, and fats.

What causes hyperadrenocorticism?

Most cases of hyperadrenocorticism are caused by enlargement of the adrenal cortex. The enlargement may be caused by tumours of the adrenal gland that produce adrenal hormones (15% of cases) or of the pituitary gland (located in the brain) that produce excessive ACTH, a hormone which stimulates the adrenal gland to produce corticosteroids - this form of the disease is referred to as pituitary-dependent hyperadrenocorticism and accounts for around 85% of cases. The tumours can be benign or malignant (cancerous).

The signs of hyperadrenocorticism can also be produced by the long-term, daily administration of large doses of corticosteroids. When this occurs, the disease is called "iatrogenic hyperadrenocorticism."

What are the signs of hyperadrenocorticism?

Hyperadrenocorticism is an insidious and slowly progressive disease. Signs include numerous changes to the skin and body. A pet with hyperadrenocorticism may have only a few signs or numerous signs. The severity of signs varies, depending on the duration and degree of excessive cortisol in the body. Some animals are more sensitive to the effects of excessive cortisol than others; these animals may develop signs more quickly and may have more severe disease. The signs include:

 Excessive urination (polyuria)

 Excessive thirst (polydipsia)

 Increased appetite

 Pot-bellied or bloated appearance (pendulous abdomen)

 Hair loss (alopecia) - usually symmetrical

 Rough coat

 Thin, fragile skin

 Increased skin pigmentation

 Calcified lumps in the skin

 Enlarged liver

 Panting

 Lethargy

 Muscle weakness

 Muscle atrophy

 Lack of oestrous cycles in intact females

 Testicular atrophy

 Facial nerve paralysis

The presence of either adrenal gland or pituitary tumours may cause additional signs related to the tumour itself.

How is hyperadrenocorticism diagnosed?

Firstly, a full medical history and thorough physical examination will be performed to determine what clinical signs are present. Other diseases, such as diabetes mellitus or hypothyroidism, may have similar signs. The veterinarian will differentiate hyperadrenocorticism from these other diseases based on physical examination and diagnostic testing. A variety of blood tests and urinalysis may be done to evaluate the animal. Some highly specific tests, such as dexamethasone suppression test or adrenocorticotrophin (ACTH) stimulation test, may be performed to provide a definitive diagnosis and to determine whether an adrenal gland or pituitary tumour is present.

Radiographs (X-rays) of the abdomen and chest may help detect primary tumours and metastasis (the spread of the cancer to other parts of the body). Other imaging techniques such as ultrasound are often useful.

Pets with hyperadrenocorticism may have additional medical problems, such as diabetes mellitus or urinary tract infections. These problems may be identified at the same time or after the hyperadrenocorticism is diagnosed.

How is hyperadrenocorticism treated?   

Hyperadrenocorticism can be treated medically or surgically. If an adrenal tumour is found the treatment of choice is surgical removal, usually by a specialist surgeon. However, medical treatment can also be effective.

Dogs with pituitary-dependant hyperadrenocorticism can be managed medically by oral administration of certain drugs e.g mitotane. The animal may need hospitalisation during initial treatment if the clinical signs are severe. Follow-up examinations and blood tests will be necessary to monitor the pet and to evaluate response to treatment. Medication is required lifelong.

Once treatment has commenced the clinical signs of hyperadrenocorticism generally resolve quite rapidly. Initially, water consumption, frequency of urination, and appetite are reduced. Muscle strength and physical activity increase within a few weeks, and substantial hair regrowth usually occurs in 2-5 months.

What is the prognosis for animals with hyperadrenocorticism?

Many cases survive well for several years depending on the pathology present and severity of signs.

In most cases, animals with pituitary-dependant hyperadrenocorticism have a good prognosis with appropriate treatment. If these pets survive more than six months after the disease is controlled, they tend to die of causes unrelated to their hyperadrenocorticism. Medications may control the disease for 2-4 years. Untreated hyperadrenocorticism is generally a progressive disorder with a poor prognosis.

The outcome for animals with malignant adrenal gland tumours can be good, if the cancer is small and has not spread. Pets with large cancers or adrenal gland tumors with widespread metastases generally have a poor prognosis.

Content editor: Dr Julia Adams BVSc