Hyperadrenocorticism in dogs, commonly known as Cushing’s disease, is one of the most frequent hormonal disorders in middle-aged to older dogs (typically over 6 years). It is characterized by excessive production of cortisol, a hormone similar to cortisone.

In 80-85% of cases, this excess cortisol is due to a benign tumor in the pituitary gland (a small brain gland), overstimulating the adrenal glands (located near the kidneys). In about 15% of cases, it results from a benign or malignant adrenal gland tumor.

Some breeds are more prone to Cushing’s disease, including Poodles, Dachshunds, Boxers, Boston Terriers, and Beagles. Larger breeds are more susceptible to adrenal gland tumors.

Symptoms of Cushing’s Disease in Dogs

Common clinical signs include:

• Increased thirst and urination (polydipsia/polyuria)
• Excessive appetite
• Swollen abdomen and abdominal obesity
• Symmetrical hair loss (alopecia) and skin problems
• Fatigue, muscle weakness, and lethargy
• Panting
• Elevated liver enzymes and enlarged liver
• Reproductive disorders
• Neurological signs (in cases of pituitary macroadenoma large enough to compress brain structures)

Diagnosing Hyperadrenocorticism in Dogs

Diagnosis begins with a veterinary clinical exam and blood tests. A precise diagnosis requires specialized hormonal tests, such as:

• Low-dose dexamethasone suppression test
• Urinary cortisol/creatinine ratio

Once confirmed, identifying the cause (pituitary or adrenal) is essential to select appropriate treatment. Additional tests may include:

• Abdominal ultrasound
• Endogenous ACTH levels
• MRI or CT scans (ideal for detecting pituitary tumors or adrenal tumor metastases)

A urine test is also recommended, as about 50% of Cushing’s dogs develop urinary infections masked by cortisol’s anti-inflammatory effects.

Treatment Options for Cushing’s Disease

Treatment choices depend on the disease’s origin:

• Adrenal tumor:
  • Surgical removal if operable.
  • Medication if surgery is not feasible.
• Pituitary tumor:
  • Pituitary surgery (common in Europe but complex and performed at specialized centers).
  • Trilostane, the most common medication, blocks cortisol production.
  • Mitotane, previously common, now reserved for specific cases (e.g., inoperable tumors).
  • Radiation therapy may be considered for macroadenomas.

Monitoring and Prognosis

Monitoring treated dogs involves:

• Regular clinical checks (thirst, appetite, urination)
• Hormone tests (ACTH stimulation)
• Electrolyte monitoring to detect possible adrenal insufficiency (Addison’s disease)
• Blood tests 10-14 days after starting treatment, then at 1, 3, and 6 months intervals

Prognosis depends on disease cause:

• Pituitary Cushing’s: Good unless macroadenoma is present.
• Adrenal Cushing’s: Good if tumor is fully removed and there are no metastases.

On average, life expectancy post-diagnosis is approximately 1.7 years. However, most dogs living longer than 6 months usually succumb to unrelated conditions. Common complications include:

• Diabetes mellitus
• Hypertension
• Chronic urinary infections
• Pulmonary thromboembolism
• Neurological disorders in advanced pituitary tumors

Conclusion

With accurate diagnosis, effective treatment, and careful monitoring, dogs with Cushing’s disease can maintain a good quality of life.