Cushing’s disease, also referred to as hypercortisolism and hyperadrenocorticism, poses a significant health concern primarily for middle-aged and senior dogs. Left untreated, it can lead to severe complications. Here’s a comprehensive overview of Cushing’s disease in dogs, covering its various types, symptoms, treatment options, and necessary care.
What Is Cushing's Disease in Dogs?
Cushing’s disease in dogs, also known as hyperadrenocorticism, typically arises when the adrenal gland produces an excessive amount of the stress hormone cortisol.
Causes
Cushing’s disease in dogs commonly occurs in middle-aged to older dogs, typically ranging from 7 to 12 years of age. There are three primary types of Cushing’s Disease in dogs:
Pituitary-Dependent Cushing’s Disease:
This type results from a pituitary gland tumor located at the base of the brain. The tumor secretes excessive amounts of the hormone that stimulates the adrenal gland to produce cortisol. Although typically benign and small, approximately 15-20% of dogs with pituitary tumors may develop neurological symptoms as the tumor enlarges. Pituitary tumors account for 80-85% of Cushing’s disease cases.
Adrenal Gland Tumor:
Adrenal gland tumors, whether benign or malignant, affect around 15-20% of Cushing’s disease cases. These tumors occur in the adrenal glands, which produce stress hormones and are positioned next to the kidneys.
Iatrogenic Cushing’s Disease:
This type of Cushing’s disease in dogs results from the excessive or prolonged use of corticosteroid medications.
What Does Cushing's Disease Do to Dogs?
While not inherently causing pain, Cushing’s disease in dogs, particularly when uncontrolled, may lead to various complications, including:
- Elevated blood pressure
- Formation of bladder stones
- Onset of diabetes
- Persistent skin and urinary tract infections
- Liver changes, such as vacuolar hepatopathy
- Increased susceptibility to blood clot formation
- High blood pressure and protein loss in urine, which can contribute to kidney disease
- Approximately 15–20% of dogs with pituitary tumors experience neurological symptoms as the tumor enlarges, and 5–10% of dogs with Cushing’s disease also develop diabetes.
- Although rare, dogs with Cushing’s disease are at risk of pulmonary thromboembolisms, which are potentially fatal blood clots in the lungs.
Are Certain Breeds Predisposed to Cushing’s Disease?
While Cushing’s disease can affect any dog, certain breeds are more predisposed to the condition. It is frequently diagnosed in the following breeds:
- Poodles, particularly Miniature Poodles
- Dachshunds
- Boxers
- Boston Terriers
- Yorkshire Terriers
- American Staffordshire Terriers
Symptoms
Cushing’s disease in dogs presents with a range of symptoms. Among the most frequent signs are:
- Increased water consumption
- Heightened urination
- Enhanced appetite
- Hair loss or inadequate regrowth
- Excessive panting
- Appearance of a pot-belly
- Thinning of the skin
- Formation of blackheads
- Recurrent skin infections
- Recurrent urinary infections
- Sudden onset of blindness
- Lethargy
- Urinary incontinence
- Presence of seborrhea or oily skin
- Development of firm, irregular plaques on the skin, known as calcinosis cutis
Diagnosis
While there isn’t a single test that can diagnose Cushing’s disease in dogs with 100% accuracy, your veterinarian may suggest a combination of the following diagnostic procedures:
- Baseline bloodwork (CBC/Chemistry)
- Urinalysis with or without urine culture (to rule out urinary tract infections)
- ACTH stimulation test (although it may yield false negatives)
- Low-dose dexamethasone suppression test (which can be influenced by other underlying illnesses)
- High-dose dexamethasone suppression test
- Urine cortisol to creatinine ratio
- Abdominal ultrasound (to detect liver changes and adrenal gland enlargement or tumors)
- Computerized tomography scan or magnetic resonance imaging of the brain (to identify pituitary tumors)
Treatment
The treatment for Cushing’s disease in dogs varies depending on the underlying cause. Treatment options include:
Surgery: Adrenal tumors can often be surgically removed, and if benign, surgery can be curative. Pituitary tumors, located at the base of the brain, are more challenging to remove surgically but may be an option at some referral veterinary hospitals.
Medication: Medical management with trilostane (Vetoryl®) or mitotane (Lysodren®) is commonly used for pituitary tumors and when surgery isn’t feasible for adrenal tumors. These drugs disrupt cortisol production, but close monitoring is crucial to prevent excessive impairment of adrenal function. Dosage adjustments and regular monitoring through ACTH stimulation tests every three to six months are necessary as the tumors progress.
Radiation: Radiation treatment for pituitary-dependent Cushing’s disease can alleviate neurological symptoms and improve prognosis, especially if administered early. The median survival time post-radiation therapy is around 743 days, or roughly two years. Radiation therapy may also be considered for adrenal tumors that cannot be surgically removed.
How Long Do Dogs with Cushing's Disease Live?
The life expectancy of dogs with Cushing’s disease varies depending on several factors, including whether the condition is pituitary or non-pituitary dependent, the nature of the tumor (benign or malignant), and individual case details.
Pituitary Tumors:
- Dogs with small pituitary tumors often respond well to medical management, enjoying long-term control and a good quality of life. The median survival time for pituitary-dependent Cushing’s disease treated with trilostane or mitotane is approximately two to two and a half years.
- However, if the pituitary tumor is large and impacts the brain and surrounding structures, the prognosis becomes less favorable.
Adrenal Tumors:
- About half of adrenal tumors in dogs are benign and can be cured through surgical removal. The remaining malignant tumors have a poor prognosis, especially if they have metastasized upon diagnosis.
- With treatment using trilostane or mitotane, the median survival time is around one year. Prognosis worsens for dogs with metastasized primary tumors, local vascular invasion, or tumors exceeding 5 cm in length.
Can You Prevent Cushing's Disease in Dogs?
Regrettably, it is not possible to prevent Cushing’s disease if it stems from a pituitary or adrenal gland tumor. However, the risk of developing iatrogenic Cushing’s disease can be minimized by avoiding prolonged use of high-dose steroids.