Hypoadrenocorticism (Addison’s Disease)

Overview

Hypoadrenocorticism is a disorder caused by a deficiency of two hormones called cortisol (a stress hormone) and aldosterone (a hormone which regulates the sodium and potassium levels). Both cortisol and aldosterone are produced by the adrenal glands, which are located inside the abdomen, near the kidneys. This disease is most often caused by immune-mediated destruction of the adrenal glands.

Signs & Symptoms

When hypoadrenocorticism occurs, it usually affects young to middle aged female dogs, although any dog at any age can be affected. Certain breeds, such as Standard poodles, Portuguese water dogs, and West Highland white terriers have an increased risk of developing this disease. Symptoms vary and can involve many different body systems.

Intermittent lethargy, vomiting, and diarrhea are common signs.
A marked increase in thirst and urination is often noted in the days to weeks before diagnosis, and the patients can become dehydrated.
Many dogs present in shock or collapsed; this is called an Addisonian crisis.

Because the symptoms of Addison’s disease mimic other problems and often respond temporarily to nonspecific treatment, it may take a while to reach the diagnosis.

Diagnosis

A marked increase in potassium and a decrease in sodium are seen in patients with aldosterone deficiency on routine blood work, while other, less specific, findings include changes in the white blood cell count, decreases in blood proteins, glucose and cholesterol or increases in kidney values. Definitive diagnosis is made by an ACTH stimulation test. This blood test stimulates the adrenal glands to produce cortisol. In a patient with Addison’s disease, the adrenal glands can’t respond, and the hormone levels are very low or non-existent.

Treatment & Aftercare

Initial treatment may include fluid therapy and other emergent interventions to stabilize the patient.
Long-term treatment is aimed at the restoration of the hormonal deficiency (both cortisol and aldosterone).
Prednisone is typically used to replace cortisol.
Either fludrocortisone or DOCP is administered to replace aldosterone.

Patients on these medications should have electrolyte (sodium, potassium and chloride) values checked frequently until a stable dose has been reached. The prednisone dose may need to be increased during times of stress, such as veterinary or grooming appointments, travel, or moving. Prednisone must typically be given every day to control the disease. Fludrocortisone must also be given daily, while DOCP is usually administered every 3-4 weeks. The dose and the interval between injections are adjusted to the patient’s needs based on veterinary supervision. The dose and frequency of both of these drugs may need to be adjusted based on electrolyte monitoring.

The prednisone dose is generally adjusted based on clinical signs. Signs of prednisone deficiency include:

Decreased appetite
Decreased energy level
Vomiting
Diarrhea
Weakness

Signs of prednisone excess include:

A marked increase in appetite
A marked increase in thirst and urination
Muscle wasting
Pot-bellied appearance
Thinning hair coat

There is also an atypical form of Addison’s disease in which the body is only deficient in cortisol. These patients are often lethargic, have poor appetites along with weight loss, vomiting, and diarrhea. This form of Addison’s is also diagnosed by an ACTH stimulation test. Prednisone therapy is started right away, and the electrolytes are carefully monitored to evaluate the patient for aldosterone deficiency.

Prognosis

As long as the patient is receiving the cortisol and aldosterone replacement therapy, their quality of life is excellent. Anything that prevents the medications being given must be considered an emergency. Even minor illnesses can be life threatening for a patient with Addison’s disease. In times of illness, the patient may not be able to take pills and cannot compensate for the stress of the illness, which can lead rapidly to an Addisonian crisis.

Fortunately, the prognosis for Addison’s disease is generally excellent. Most patients with Addison’s disease lead full and long lives.