Addison’s Disease (Hypoadrenocorticism) in Dogs

Addison's disease is an uncommon condition that mostly affects young to middle aged dogs. It is progressive. In some cases, the symptoms are sufficiently noticeable to be brought to a veterinarian’s attention before a crisis occurs.

Most cases of Addison's disease show vague or mild symptoms, which may result in the condition going untreated for long periods of time. In these cases, untreated Addison's disease can reach a crisis.

Addisonian crisis is an emergency that requires immediate veterinary care to mitigate permanent tissue damage and death. Addisonian crisis typically occurs in times of high emotional or physical stress. The body depletes its stock of hormones that regulate energy production and water levels. Without these hormones, the body is left without the necessary energy and/or water to continue coping with the body’s demands, causing blood volume to drop and exhaustion of energy stores. Ultimately, this leads to shock and collapse.

The severity of Addison's disease depends on how much damage to the adrenal cortex has occurred, and whether it is the atypical form of the disease. Dogs with the typical form have disruption to multiple types of steroid production and are more likely to progress to Addisoinian crisis.

In cases where the atypical form is present, only one type of steroid production is disrupted. These dogs do not usually progress to Addisonian crisis.

Addison's disease is caused by one of two underlying issues: damage to the adrenal gland in the kidneys (primary Addison's disease) or damage to the pituitary gland in the brain (secondary Addison's disease).

In cases of primary Addison’s disease, the cause of the damage to the adrenal glands is often unknown. There is evidence that in some cases it results from an autoimmune response where the body attacks its own adrenal glands. There is also some evidence of a genetic component. Other potential causes of damage to the adrenal glands include:

• Tumors
• Blood clots
• Hemorrhage
• Inflammatory conditions
• Side effect of medications

Secondary Addison's disease is caused by damage to the pituitary gland. The pituitary gland is a part of the brain that secretes Adrenocorticotropic hormone (ACTH), which controls production of stress hormones by the adrenal glands. When the level of ACTH in the bloodstream drops, the adrenal glands stop making these hormones. If left without ACTH for too long, the adrenal glands atrophy and the production of stress hormones is disrupted.

Potential causes of damage to the pituitary gland include:

• Tumors
• Inflammation
• Traumatic injury
• Side effect of long-term corticosteroid use

The symptoms of Addison's disease are extremely variable, and tend to wax and wane in relation to stress. They are also non-specific, which makes this condition very difficult to diagnose.

In cases where Addisonian crisis has not occurred but symptoms are present, prompt veterinary care is required. Since symptoms are variable, intermittent and non-specific, a diagnosis of Addison's can take time and diligence to achieve. Diagnosis of Addison's disease often requires ruling out other potential causes of the symptoms.

Diagnostic tools include:

• Physical exam
• Blood tests
• Urinalysis
• Electrocardiogram (heart tests)
• Diagnostic imaging, such X-rays or ultrasound

When other causes have been excluded, an ACTH stimulation test is administered. This consists of injecting synthetic ACTH into the bloodstream, stimulating the adrenal cortex to produce stress hormones. The levels of these hormones in the body are then measured. If the hormones increase in response to ACTH, an official diagnosis of Addison's disease is made.

In cases where Addison's disease develops into Addisonian crisis prior to diagnosis, emergency veterinary care is required. Treatment for Addisonian crisis includes the restoration of blood volume through IV fluids, and correction of sodium and potassium levels.

Treatment aims to rebalance hormone levels in the body. Synthetic hormones are prescribed for daily administration. In times of stress, additional hormone supplementation may be required under veterinary supervision.

Careful weekly or bi-weekly monitoring of hormone levels, as well as potassium and sodium levels, is necessary for the first few months after treatment begins. Once an appropriate dose of supplemented hormones has been found, monitoring once or twice a year is sufficient. Pharmaceutical management is necessary for the remainder of life.

There is no cure for Addison's disease. Without hormone supplementation, the condition is fatal. Careful lifelong management with routine monitoring of hormone levels carries a good to excellent prognosis.

There are no proven preventative measures for Addison's disease.

Addison's disease is uncommon in dogs.

• Synthetic hormones
• IV fluids
• Electrolytes