Addison’s Disease (Hypoadrenocorticism)

Addison’s Disease in Dogs: Understanding Hypoadrenocorticism

Addison’s disease, also known as hypoadrenocorticism, is a hormone deficiency that affects a dog’s ability to regulate stress, hydration, and electrolyte balance. This condition occurs when the adrenal glands stop producing enough of two critical hormones: cortisol and aldosterone.

The term hypoadrenocorticism breaks down into its parts:

• Hypo means “low” or “too little”
• Adreno refers to the adrenal glands, which sit above the kidneys
• Corticism relates to the adrenal cortex, the outer layer of the adrenal glands where hormones are produced

When the adrenal glands stop working properly, the body can no longer maintain internal balance. The result is a condition that can affect nearly every major system, including the digestive tract, cardiovascular function, immune response, and overall energy levels.

Recognizing the Signs of Addison’s Disease in Dogs

The early signs of Addison’s disease in dogs often look mild or vague. Dogs may seem tired, pick at their food, or experience loose stool. Some have waxing and waning digestive upset that resolves, only to return days or weeks later. These episodes can mimic everything from dietary sensitivity to stress-related diarrhea.

As hormone levels continue to drop, symptoms tend to escalate. Dogs may show signs of nausea, trembling, or depression. Some experience sudden collapses, often during travel, boarding, or illness—situations that would normally trigger a healthy dog’s stress response.

Because the adrenal hormones play such a broad role in body regulation, Addison’s can affect many systems at once. Clinical signs may include:

• Low or inconsistent energy
• Vomiting or diarrhea
• Weakness or shakiness
• Dehydration
• Loss of appetite or unexplained weight loss
• Increased thirst or urination
• Slow heart rate or irregular rhythm
• Collapse or signs of shock

Dogs in an Addisonian crisis can present as flat, cold, and unresponsive. Without emergency treatment, the condition can become fatal.

Addison’s Disease or Intestinal Obstruction?

Addison’s disease can resemble other medical emergencies. In some dogs, the first signs mimic a gastrointestinal blockage. A dog may hunch, refuse food, vomit repeatedly, or strain during bowel movements. Caregivers may assume the dog swallowed a toy, chewed something sharp, or ate something toxic.

Veterinarians may also suspect obstruction based on the dog’s abdominal discomfort, bloating, or slowed gut motility. Radiographs or ultrasound sometimes show gas buildup or slowed intestinal movement that looks like a blockage, but no foreign body is found.

This is why Addison’s disease is sometimes called “the great imitator.” It mimics surgical emergencies, kidney failure, pancreatitis, and other systemic illnesses. When a dog shows sudden GI signs with abnormal heart rate, dehydration, or vague lab findings, Addison’s should stay on the diagnostic list.

Atypical Addison’s Disease in Dogs

Some dogs develop Addison’s disease without changes in sodium or potassium. This form is known as atypical Addison’s disease. These dogs fail to produce cortisol but retain normal aldosterone levels, so their electrolyte values may look normal.

Atypical Addison’s can present with vague symptoms:

• Poor appetite
• Lethargy
• Intermittent vomiting or diarrhea
• Poor recovery from stress
• General disinterest in activity

Because standard bloodwork may appear normal, these dogs are often misdiagnosed or treated for unrelated GI problems. The key to identifying atypical Addison’s lies in cortisol testing. If a dog has chronic or recurring signs without clear explanation, a veterinarian may order a baseline cortisol or ACTH stimulation test to confirm.

Some dogs with atypical Addison’s eventually lose aldosterone production and transition into the typical form. Regular monitoring can help catch this shift before a crisis develops.

What Causes Addison’s Disease in Dogs?

In most cases, Addison’s disease results from immune-mediated destruction of the adrenal glands. The body mistakenly attacks its own adrenal tissue, leaving the glands unable to produce hormones. This is known as primary hypoadrenocorticism.

Less commonly, Addison’s disease can result from:

• Long-term steroid use that suppresses natural hormone production
• Sudden withdrawal from corticosteroids without tapering
• Tumors or infections affecting the adrenal glands or pituitary
• Genetic or congenital adrenal underdevelopment (especially in young dogs)

No matter the cause, the result is the same: the dog cannot produce the hormones needed to handle stress or maintain stable hydration and electrolyte levels.

Diagnosing Hypoadrenocorticism in Dogs

Because Addison’s disease mimics so many other conditions, diagnosis requires specific testing. A veterinarian may begin with:

• Electrolyte panel: Low sodium and high potassium suggest Addison’s
• Baseline cortisol: Low resting cortisol levels support suspicion
• ACTH stimulation test: Confirms diagnosis by testing adrenal response to stimulation

The ACTH test remains the gold standard. In healthy dogs, the adrenal glands respond to ACTH with a surge in cortisol. In Addisonian dogs, cortisol levels remain low before and after stimulation.

Additional diagnostics may include:

• Complete blood count (CBC)
• Chemistry panel
• Urinalysis
• Imaging to rule out obstruction, kidney disease, or structural issues
• ECG if abnormal heart rhythms are present

A correct diagnosis opens the door to immediate stabilization and lifelong treatment.

Treatment for Addison’s Disease in Dogs

Addison’s disease requires lifelong hormone replacement. Once treatment begins, most dogs regain normal energy, appetite, and hydration levels.

Treatment includes:

• Cortisol replacement with daily prednisone or another steroid
• Aldosterone replacement (for typical Addison’s) using monthly DOCP injections or daily fludrocortisone
• Routine bloodwork to monitor electrolytes and adjust doses
• Stress management during illness, surgery, or travel

Most dogs stabilize quickly after treatment begins. Some may need dose adjustments over time, especially during growth, seasonal changes, or periods of increased stress.