What is Addison’s disease?
Addison’s disease, also known as hypoadrenocorticism, is a disorder of the adrenal glands resulting in insufficient levels of stress hormone (cortisol) and, typically, electrolyte balancing hormone (aldosterone). Young to middle-aged female dogs are most likely to develop Addison’s disease, but it can occur at any age and in either gender. Similarly, standard poodles, Portuguese water dogs, and Nova Scotia duck tolling retrievers are predisposed to Addison’s, as are (to a lesser extent) Great Danes, West Highland white terriers, bearded collies, rottweilers, soft-coated wheaten terriers, and Leonbergers, although Addison’s may occur in any breed. Addison’s rarely occurs in cats.
What are the clinical signs of Addison’s disease?
Dogs with Addison’s commonly have a history of intermittent to chronic weakness, lethargy, anorexia, and vomiting. Due to the lack of stress hormone, Addisonian dogs do not handle stressful situations well and often have exacerbated clinical signs at those times. As the disease progresses, some dogs may develop weight loss, trembling, increased water intake and urination, intermittent regurgitation, and eventually severe, acute, and potentially fatal episodes of collapse. During these episodes, affected dogs may develop seizures secondary to low blood sugar, a low heart rate due to elevated blood potassium, and shock from low blood volume and pressure.
What causes Addison’s disease?
The adrenal hormone insufficiency of Addison’s is caused by immune-mediated destruction of the adrenal glands. There are other, less common causes of adrenal gland destruction, including but not limited to fungal infection, compromised blood supply, cancer, abnormal protein deposition, and certain drugs (namely long-term steroids and those used to treat Cushing’s disease, AKA hyperadrenocorticism). Rarely, disease of the pituitary gland can cause loss of signal to the adrenal glands and a secondary Addison’s disease.
How do we test for Addison’s disease?
When a veterinarian is assessing a dog with a history and physical exam consistent with Addison’s disease, there are multiple diseases (kidney disease, cancer, etc) that must be ruled out prior to more definitive testing to confirm Addison’s disease. The initial diagnostic tests typically include a complete blood count, blood chemistry, and urinalysis, revealing anemia (low red blood cell count), a lack of an appropriate stress response among white blood cells, low blood sodium, high blood potassium, and poorly concentrated urine. In dogs with “atypical” Addison’s, there are no sodium and potassium derangements, although these may develop as the disease progresses.
An ECG (electrocardiogram) may be completed depending on the degree of potassium elevation to ensure no secondary arrhythmias. Chest radiographs and abdominal ultrasounds are also indicated to screen for signs of cancer and, in the Addisonian dog, can reveal a small heart due to low blood volume, an enlarged esophagus, possible pneumonia secondary to regurgitation and aspiration, and small adrenal glands. Finally, a baseline cortisol measurement can serve to rule out Addison’s disease, but an “ACTH Stimulation Test” must be completed to confirm Addison’s disease. This test involves injecting the patient with artificial ACTH, the hormone responsible for stimulating cortisol release from the adrenal glands, and measuring the cortisol levels before and 1-2 hours after.
How is Addison’s disease treated?
There is no cure for Addison’s disease – the destruction of the adrenal glands is unfortunately irreversible. Dogs with Addison’s are instead managed with supplementation of their deficient hormones for the remainder of their life. Cortisol, the stress hormone, is supplemented with a daily prednisone pill at a physiologic dose. Aldosterone, the electrolyte-balancing hormone, is supplemented with an injection of Percorten-V (AKA deoxycorticosterone pivalate) once every 25 days. However, with close initial electrolyte monitoring some dogs can go longer between injections. A blood chemistry and electrolyte panel are typically initially checked weekly, then monthly, then once every 3-6 months for life.
Dogs suffering from an Addisonian crisis will require stabilization prior to initiating long-term management. Stabilization typically involves hospitalization, IV fluids for low blood volume and pressure, injectable steroids, and specific treatments for elevated blood potassium and low blood sugar if severe enough. While hospitalized, urine production, serum electrolytes, and blood glucose are all monitored closely to ensure an appropriate response to therapy. Patients are discharged once they are eating well and their potassium and glucose have normalized.
If my dog develops Addison’s disease, what can I expect?
Well-managed dogs with Addison’s disease have an excellent prognosis and normal lifespan, although complications from both the disease and its treatment can occur. Long-term prednisone use can result in increased water intake and weight gain, but this is typically mitigated with appropriate dose tapering. Alternatively, failure to continue life-long prednisone and Perortin-V supplementation can lead to a potentially fatal Addisonian crisis.
