Cushing\'s Disease in Dogs: Symptoms, Diagnosis, and Treatment

Cushing\'s disease, known medically as hyperadrenocorticism, occurs when a dog\'s body produces too much cortisol. Cortisol is essential in normal amounts, regulating metabolism, immune response, and stress reactions. But when the adrenal glands produce excessive cortisol over time, it affects virtually every system in the body. This condition primarily affects middle-aged and older dogs, typically those over six years old.

Types of Cushing\'s Disease

There are three forms of Cushing\'s disease in dogs, each with a different underlying cause:

Pituitary-Dependent (80-85% of cases)

A small, usually benign tumor on the pituitary gland at the base of the brain overproduces ACTH (adrenocorticotropic hormone), which signals the adrenal glands to produce more cortisol. This is by far the most common form.

Adrenal-Dependent (15-20% of cases)

A tumor on one of the adrenal glands directly overproduces cortisol. These tumors can be benign or malignant, and the distinction significantly affects prognosis and treatment options.

Iatrogenic Cushing\'s

Caused by long-term use of corticosteroid medications (like prednisone). The external steroids mimic excess cortisol production. This form resolves when the medication is gradually tapered under veterinary supervision.

Recognizing the Symptoms

Cushing\'s disease develops gradually, and many owners attribute early signs to normal aging. Learning to recognize the symptoms can lead to earlier diagnosis and better outcomes.

Classic Early Signs

• Increased thirst and urination: Often the first sign noticed. Dogs may drink two to three times their normal water intake and need to go outside much more frequently, including overnight.
• Increased appetite: Dogs may become ravenous, beg constantly, or steal food. This is directly caused by elevated cortisol.
• Pot-bellied appearance: One of the most characteristic signs. The abdomen becomes distended due to fat redistribution, liver enlargement, and weakened abdominal muscles.

Progressive Symptoms

• Hair loss (bilateral and symmetrical): Typically affects the trunk, flanks, and neck while sparing the head and legs
• Thin, fragile skin: The skin becomes paper-thin and bruises easily
• Recurrent skin infections: Cortisol suppresses the immune system, making infections more frequent
• Muscle weakness and wasting: Especially noticeable in the hind legs. Dogs may struggle to climb stairs or jump.
• Panting (excessive): Even at rest and in cool temperatures
• Lethargy and reduced activity: Despite the increased appetite, dogs often become less energetic
• Darkening of the skin (hyperpigmentation): Particularly on the belly

Diagnosis

Diagnosing Cushing\'s disease requires multiple tests because no single test is definitive:

• Routine blood work and urinalysis: May show elevated liver enzymes (especially alkaline phosphatase), dilute urine, elevated cholesterol, and elevated blood sugar
• Urine cortisol:creatinine ratio (UC:CR): A screening test. A normal result effectively rules out Cushing\'s, but an elevated result requires further testing.
• Low-dose dexamethasone suppression test (LDDS): The most commonly used confirmatory test. Measures how the body\'s cortisol production responds to a synthetic steroid injection over 8 hours.
• ACTH stimulation test: Measures how the adrenal glands respond to synthetic ACTH. Also used to monitor treatment effectiveness.
• Abdominal ultrasound: Evaluates the size and shape of the adrenal glands. Can identify adrenal tumors and distinguish between pituitary and adrenal forms.
• MRI (if available): Can identify pituitary tumors, useful for treatment planning.

Treatment Options

For Pituitary-Dependent Cushing\'s

Trilostane (Vetoryl): The most commonly prescribed medication. It inhibits cortisol production in the adrenal glands. Requires careful dose adjustments and regular monitoring with ACTH stimulation tests. Most dogs show improvement within 2-4 weeks.

Mitotane (Lysodren): An older medication that selectively destroys the cortisol-producing layer of the adrenal glands. Effective but requires careful monitoring due to the risk of destroying too much adrenal tissue.

For Adrenal-Dependent Cushing\'s

Surgery (adrenalectomy): Removing the affected adrenal gland is potentially curative if the tumor is benign. This is a complex surgery that requires an experienced surgeon and carries significant risks.

Medical management: Same medications as pituitary-dependent if surgery isn\'t feasible.

For Iatrogenic Cushing\'s

Gradual tapering of the corticosteroid medication under close veterinary supervision. Never stop corticosteroids abruptly, as this can cause a life-threatening adrenal crisis.

Living with Cushing\'s Disease

With proper treatment, most dogs with Cushing\'s disease can enjoy a good quality of life. Key management strategies include:

1. Regular veterinary monitoring: ACTH stimulation tests every 3-6 months to adjust medication doses
2. Watch for signs of under- or over-treatment: Over-treatment can cause lethargy, vomiting, diarrhea, and weakness (signs of Addison\'s disease)
3. Manage secondary conditions: Dogs with Cushing\'s are more prone to urinary tract infections, digestive issues, skin infections, and diabetes
4. Maintain gentle exercise: Moderate activity helps maintain muscle mass without overexertion
5. Monitor skin health: Regular grooming and prompt treatment of any skin infections

If you notice your older dog drinking more water, developing a pot belly, or losing hair symmetrically, don\'t wait. Early diagnosis leads to earlier treatment and better outcomes. Schedule a veterinary appointment and mention your concerns about Cushing\'s disease specifically. For more on monitoring your dog\'s health, see our dog care basics guide.