Cushing Disease in Dogs – Symptoms, Causes, Diagnosis & Treatment

Cushing’s disease, medically known as hyperadrenocorticism (HAC), represents one of the most frequently diagnosed endocrine disorders in middle-aged and senior dogs. The condition develops when a dog’s body produces excessive amounts of cortisol, a steroid hormone that plays essential roles in regulating metabolism, immune function, and stress response. When left untreated, persistently elevated cortisol levels can damage multiple organ systems and substantially diminish a dog’s quality of life. Understanding the causes, recognizing the symptoms, and pursuing appropriate diagnostic and treatment approaches can help pet owners manage this chronic condition effectively and support their companion animals through adjusted care strategies and veterinary oversight.

The disorder affects dogs across all breeds, though certain genetic predispositions exist that make some canine families more susceptible than others. Advances in veterinary diagnostics have enabled earlier detection, allowing for more timely intervention before irreversible organ damage occurs. Treatment options range from medication management to surgical intervention, with the optimal approach depending on the underlying cause and the individual dog’s health status.

What Is Cushing’s Disease in Dogs and What Causes It?

Cushing’s disease in dogs stems from a fundamental breakdown in the normal feedback mechanism that regulates cortisol production. In healthy animals, the pituitary gland monitors cortisol levels in the bloodstream and adjusts its output of adrenocorticotropic hormone (ACTH) accordingly. When cortisol reaches sufficient concentrations, the pituitary normally signals the adrenal glands to reduce their production. In dogs with Cushing’s disease, this regulatory system fails, resulting in continuous overproduction of cortisol by the adrenal glands.

Veterinary researchers have identified three distinct forms of Cushing’s disease, each with different underlying mechanisms and treatment implications. Understanding which type affects a particular dog is essential for developing an effective management plan.

Pituitary-Dependent Hyperadrenocorticism (PDH)

The most prevalent form of Cushing’s disease in dogs, pituitary-dependent hyperadrenocorticism accounts for approximately 80 to 90 percent of all diagnosed cases. This condition develops when a small, typically benign tumor forms on the pituitary gland—a pea-sized structure located at the base of the brain. The tumor cells produce ACTH without responding to the normal feedback signals that would otherwise suppress their activity. This excessive ACTH travels through the bloodstream and continuously stimulates the adrenal glands, causing them to enlarge and produce surplus cortisol. In roughly 15 percent of dogs with PDH, the pituitary tumor may grow large enough to affect surrounding brain tissue, potentially causing neurological symptoms and a less favorable long-term prognosis.

Adrenal-Dependent Hyperadrenocorticism

Adrenal-dependent Cushing’s disease represents approximately 15 to 20 percent of cases and results from a tumor that develops directly on one or both adrenal glands. Unlike the pituitary form, the adrenal glands themselves become the source of excessive cortisol production. The affected gland typically appears enlarged on diagnostic imaging, while the opposite adrenal gland remains normal in size. These tumors may be either benign or malignant, with the prognosis varying considerably depending on whether the growth has spread beyond the adrenal region.

Iatrogenic Cushing’s Disease

The third form of Cushing’s disease occurs as a side effect of prolonged treatment with corticosteroid medications such as prednisone. When dogs receive high doses or extended courses of these drugs—whether for autoimmune conditions, allergic reactions, or inflammatory disorders—the adrenal glands can become suppressed and subsequently atrophied. Abruptly discontinuing such medications can trigger a rebound effect as the body attempts to resume normal cortisol production. This medication-induced form is potentially reversible if identified early and managed under close veterinary supervision.

What Are the Symptoms of Cushing’s Disease in Dogs?

The clinical signs of Cushing’s disease in dogs develop gradually and can be mistaken for normal aging changes, which often delays diagnosis. The constellation of symptoms results from cortisol’s widespread effects on nearly every organ system in the body. Pet owners should monitor their dogs closely for any combination of these signs, particularly if multiple symptoms appear simultaneously or progressively worsen over time.

Increased thirst and urination (polydipsia and polyuria) typically represent the earliest and most noticeable changes. Dogs may begin demanding water more frequently, urinating in larger volumes, or having accidents in the house despite being previously housebroken. This excessive thirst and urination occurs because elevated cortisol disrupts the kidneys’ normal concentrating ability.

• Increased thirst and urination beyond normal
• Excessive appetite that may seem insatiable
• Hair loss, particularly along the flanks and trunk
• Dull, brittle, or thinning coat quality
• Pot-bellied or distended abdominal appearance
• Excessive panting, especially at rest or in cool conditions
• Reduced energy levels and reluctance to exercise
• Heat sensitivity and seeking cooler surfaces
• Skin changes including thinning, darkening, or calcified patches
• Muscle weakness causing difficulty climbing stairs or jumping

Skin manifestations extend beyond hair loss to include calcinosis cutis—firm, chalky deposits beneath the skin that appear as raised plaques or nodules. The skin itself often becomes thin and fragile, bruising more easily and healing more slowly from minor injuries. Secondary skin infections may develop due to cortisol’s immunosuppressive effects, presenting as redness, pustules, or itchy patches that resist typical treatment approaches.

Neurological symptoms emerge in dogs whose pituitary tumors have grown large enough to press on surrounding brain structures. These signs may include head pressing, disorientation, circling, vision changes, seizures, or alterations in appetite and behavior. Such neurological involvement generally indicates a more serious prognosis and may necessitate additional interventions beyond standard medical management.

How Is Cushing’s Disease Diagnosed and Treated in Dogs?

Diagnosing Cushing’s disease requires a systematic approach that confirms the presence of hyperadrenocorticism while determining its underlying cause. No single test provides a complete picture, so veterinarians typically employ a combination of screening tests, confirmatory tests, and imaging studies to establish an accurate diagnosis and guide treatment decisions.

Diagnostic Testing Procedures

Initial screening typically begins with baseline blood work including a complete blood count, chemistry panel, and urinalysis. These tests may reveal elevated liver enzymes, high cholesterol, dilute urine, or other abnormalities consistent with cortisol excess. However, these findings are not specific to Cushing’s and require more targeted testing for confirmation.

The ACTH stimulation test serves as a primary screening tool, measuring how the adrenal glands respond to an injection of synthetic ACTH. Dogs with Cushing’s disease typically show an exaggerated cortisol response, confirming adrenal dysfunction. This test also helps differentiate pituitary-dependent from adrenal-dependent cases and is useful for monitoring dogs already receiving treatment.

The low-dose dexamethasone suppression test provides additional diagnostic information by measuring cortisol levels before and after administering a low dose of dexamethasone. Healthy dogs suppress cortisol production in response to this synthetic steroid, while dogs with Cushing’s disease do not show the expected suppression. This test also offers some ability to distinguish between pituitary and adrenal causes based on the pattern of cortisol levels.

Imaging Studies

Abdominal ultrasound allows veterinarians to visualize the adrenal glands directly, assessing their size, shape, and the presence of tumors. Enlarged adrenal glands suggest pituitary-dependent disease, while asymmetric glands with a distinct mass indicate adrenal-dependent Cushing’s. Ultrasound cannot, however, definitively identify small pituitary tumors.

Advanced imaging using CT or MRI provides superior visualization of the pituitary gland and can detect tumors as small as a few millimeters. While more expensive and requiring general anesthesia, these imaging modalities offer critical information for dogs with suspected large pituitary tumors or when surgical intervention is being considered. MRI is generally preferred for pituitary evaluation due to its superior soft tissue contrast.

Medication Options

Vetoryl (trilostane) represents the only FDA-approved medication for treating both pituitary-dependent and adrenal-dependent Cushing’s disease in dogs. The drug works by inhibiting an enzyme essential for cortisol production, thereby reducing circulating hormone levels. Treatment typically begins at a low dose and requires gradual adjustment based on periodic ACTH stimulation testing to ensure adequate control while avoiding adrenal insufficiency.

Most dogs with Cushing’s disease require lifelong medication, with regular veterinary monitoring to assess treatment efficacy and adjust dosages as needed. Blood work and ACTH stimulation tests become routine components of ongoing care, typically performed every few months once stabilization is achieved. Side effects may include lethargy, reduced appetite, vomiting, or diarrhea, and owners should report any concerning changes to their veterinarian promptly.

Surgical Intervention

Surgical removal of adrenal tumors offers the only potential cure for adrenal-dependent Cushing’s disease. If the tumor is benign and hasn’t spread, complete surgical excision can resolve the condition entirely without requiring ongoing medication. The procedure is technically demanding due to the adrenal glands’ proximity to major blood vessels and requires a surgeon experienced in veterinary oncology.

Malignant adrenal tumors present a more complex challenge. Surgery may provide temporary symptom relief, but the prognosis remains guarded if metastasis has occurred. Adjunctive treatments such as chemotherapy may be considered in select cases, though evidence for their effectiveness specifically in canine adrenal carcinoma remains limited.

Radiation Therapy

Stereotactic radiation therapy has emerged as a treatment option for dogs with pituitary-dependent Cushing’s disease, particularly those with larger tumors causing neurological symptoms. This approach uses precisely targeted radiation to destroy tumor tissue while minimizing damage to surrounding brain structures. Treatment typically requires only one to three sessions under anesthesia, representing a less invasive alternative to traditional surgery for eligible candidates.

What Is the Prognosis for Dogs with Cushing’s Disease?

The prognosis for dogs diagnosed with Cushing’s disease varies considerably depending on the underlying cause, the presence of complications, the dog’s overall health status, and how effectively the condition responds to treatment. With appropriate management, many dogs enjoy a good quality of life for months to years following diagnosis.

Understanding Disease Progression

Cushing’s disease itself is not typically considered directly fatal, but its complications can significantly impact longevity and quality of life. Prolonged cortisol excess damages the immune system, making dogs more susceptible to infections. The cardiovascular system bears additional strain, potentially contributing to hypertension and heart problems. Diabetes mellitus may develop secondary to Cushing’s, requiring additional treatment and dietary management.

Kidney function can deteriorate over time due to the constant demand placed on these organs by elevated cortisol levels. Liver changes are also common, with many dogs developing fatty deposits and altered liver enzyme levels. Thromboembolic complications, where blood clots form and travel to critical organs, represent a less common but serious potential consequence of untreated or poorly controlled disease.

The timeline from diagnosis to significant symptom improvement typically spans several weeks to months once appropriate treatment begins. Dogs with iatrogenic Cushing’s may show faster improvement since discontinuing the offending medication often produces rapid results under veterinary supervision.

1. Initial presentation: Symptoms develop gradually over months; many dogs are already in advanced stages when first examined
2. Diagnostic workup: Blood tests, imaging, and stimulation tests confirm diagnosis and determine type
3. Treatment initiation: Medication begins at low doses with gradual adjustment based on response
4. Monitoring phase: ACTH stimulation tests every 2-4 weeks until stable, then every 3-6 months
5. Long-term management: Lifelong medication with regular veterinary oversight and periodic reassessment
6. Complication surveillance: Ongoing monitoring for diabetes, infections, hypertension, and other secondary conditions

Comparing Outcomes by Disease Type

Which Dog Breeds Are Prone to Cushing’s Disease?

While Cushing’s disease can develop in any dog breed, certain genetic lineages show notably higher predisposition to the condition. These breed predispositions suggest underlying hereditary factors that influence susceptibility to pituitary or adrenal tumor development. Understanding breed-specific risks can help veterinarians maintain appropriate vigilance when examining patients from high-risk populations.

High-Risk Breeds

Small breed dogs, particularly those weighing under 20 kilograms, account for the majority of Cushing’s disease cases in veterinary practice. Poodles, especially miniature and toy varieties, consistently appear at the top of epidemiological studies regarding breed predisposition. Yorkshire Terriers and Dachshunds similarly demonstrate elevated risk compared to the general canine population.

• Poodles (all sizes, particularly miniature and toy)
• Yorkshire Terriers
• Dachshunds
• Boston Terriers
• Boxers
• Labrador Retrievers
• Australian shepherds

Age and Environmental Factors

The disease predominantly affects middle-aged to senior dogs, with most diagnoses occurring between 9 and 11 years of age. The gradual onset of symptoms often leads to delays in recognition, meaning the actual disease onset may begin several years before clinical diagnosis. Very young dogs rarely develop spontaneous Cushing’s disease, though congenital forms have been reported in extremely rare instances.

The prevention of pituitary-dependent and adrenal-dependent Cushing’s disease remains impossible due to the spontaneous nature of tumor development in these cases. No dietary supplement, lifestyle modification, or environmental change has demonstrated any ability to reduce risk. Responsible breeding practices that avoid reproducing from affected lines may help reduce breed-wide incidence over generations, though the complex genetics underlying tumor susceptibility make complete elimination unlikely.

Summary

Cushing’s disease in dogs represents a complex endocrine disorder that requires lifelong management and careful veterinary oversight. The condition develops through three primary mechanisms—pituitary tumors causing approximately 80 to 90 percent of cases, adrenal tumors accounting for 15 to 20 percent, and medication-induced forms from prolonged steroid use. Recognizing the characteristic symptoms, including increased thirst and urination, hair loss, pot-bellied appearance, and reduced energy, enables earlier veterinary consultation and diagnosis.

Treatment options have expanded considerably in recent years, with Vetoryl (trilostane) serving as the primary pharmaceutical intervention for most dogs. Surgical removal of benign adrenal tumors offers the possibility of cure, while radiation therapy addresses select cases of pituitary-dependent disease with larger tumors. Consistent monitoring through ACTH stimulation testing and blood work ensures treatment efficacy and allows for timely dosage adjustments. For more information on common health conditions affecting dogs, see our guide to Weight loss as it relates to metabolic health.

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