CAUSES AND DEVELOPMENT

Cushing (Hyperadrenocorticism) can occur in three ways:

• When a pituitary gland tumor produces too much ACTH (hypohyseal hyperadrenocorticism) ;
• When an adrenal tumor produces too many glucocorticoids on its own (adrenal hyperadrenocorticism) ;
• When the dog receives an excess of exogenous glucocorticoids by way of medication (iatrogenic hyperadrenocorticism).

This disease is often diagnosed from the age of 6 but has already been documented in younger dogs. There is no predisposition associated with sex. All breeds can be affected but some are particularly predisposed such as the Poodle, Dachshund, Terrier-type breeds, German Shepherd, Beagle, Labrador Retriever and Boxer.

Pituitary hyperadrenocorticism is more commonly seen in small breed dogs (<20kg).

CLINICAL SYMPTOMS

The excess of glucocorticoids released into the blood stream has a detrimental effect on the metabolism as well as on the function of several organs. The resulting symptoms can significantly impact the dog’s quality of life and even potentially endanger it.

It is a slowly progressing disease. The most frequently observed symptoms are: polyuria-polydipsia (urinating and drinking more frequently), polyphagia (increased appetite), distended or pendular abdomen, hair loss (often bilateral and symmetrical on the flanks), thin skin, weakness. The dog is calmer and less lively than usual, and his breathing is faster and shallower.

Other, less common symptoms may appear if the tumor squeezes or invades surrounding tissue. For example, in the case of pituitary hyperadrenocorticism, when the tumor increases in size it can cause lesions in the brain and neurological symptoms can then appear such as apathy, stupor, loss of appetite, moving in a circle or aimlessly, loss of balance and behavioral problems.

Other complications may appear such as the development of diabetes mellitus, recurrent urinary tract infections and increased blood pressure. Pulmonary thromboembolism (clots that block blood vessels in the lungs) are among the rarer but worrying complications. This clinically results in the onset of acute breathing difficulty. In this case, a veterinarian must quickly be consulted.

DIAGNOSIS

Often it is a combination of several elements that makes a diagnosis of cushing possible. The clinical signs described above are a first step in suspecting this disease. Certain specific abnormalities visible on the blood test may also support clinical suspicion.

To get a definite diagnosis, a dynamic blood test, which lasts 1 to 8 hours, must be performed. This involves injecting the dog with a hormone (ACTH or glucocorticoids) and checking how the hormonal metabolism responds. This test is combined with medical imaging exams (ultrasound, CT scan, MRI) to precisely determine the type of hyperadrenocorticism. It is important to know which type is involved because the treatment options are not the same.

TREATMENTS AND PROGNOSIS

• In the case of adrenal hyperadrenocorticism, the affected adrenal gland can either be removed or treated with medication when surgery is not possible. When the adrenal tumor is benign and is excised, the prognosis is very good. It is more reserved when the adrenal tumor is malignant ;
• In the event of pituitary hyperadrenocorticism, a drug may be administered which reduces the production of glucocorticoids with a good prognosis most of the time. Excision of the pituitary tumor is also described, but it is a complex operation and is rarely performed ;
• In case of iatrogenic hyperadrenocorticism, the drug which contains glucocorticoids should be discarded. Complete healing can then be obtained.

Dr Emilie Vangrinsven
Diplomate from European college of veterinary internal medicine | PhD U-Liège
Assistant at the Liege University in the university clinic for PETs | Author and co-author of numerous scientific publications