# Cushings Disease in Dogs: Pituitary vs Adrenal Hyperadrenocorticism Guide ## Key Takeaways - Hyperadrenocorticism (Cushing's disease) in dogs stems from excessive cortisol production, primarily due to pituitary-dependent hyperadrenocorticism (PDH, ~80-85% of cases) caused by a pituitary adenoma, or adrenal-dependent hyperadrenocorticism (ADH, ~15-20% of cases) caused by an adrenal tumor. - Diagnostic confirmation of Cushing's disease involves tests like the ACTH stimulation test or low-dose dexamethasone suppression (LDDS) test, which assess cortisol response to stimulation or suppression. - Differentiating PDH from ADH is critical for treatment and is achieved through endogenous ACTH level measurement (normal/high in PDH, low/undetectable in ADH) and abdominal ultrasound findings (symmetrical adrenal enlargement in PDH, unilateral adrenal mass in ADH). - Treatment for PDH is primarily medical management with drugs like trilostane or mitotane, aiming to control clinical signs and requiring lifelong monitoring. - Surgical adrenalectomy is the preferred treatment for ADH if the tumor is benign and resectable, offering a potential cure, while medical management is an alternative, especially for malignant tumors. - Common clinical signs include polyuria/polydipsia, polyphagia, symmetrical alopecia, pot-bellied appearance, and lethargy, often progressing subtly and mimicking aging. --- If your [dog](/knowledge/veterinary-medicine/clinical-methods/dog) has been drinking excessively, urinating more frequently, developing a pot-bellied appearance, or losing hair in a symmetrical pattern, your veterinarian may suspect hyperadrenocorticism, commonly known as Cushing's disease. This condition arises from the prolonged overproduction of cortisol, a vital steroid hormone. The two most common forms are pituitary-dependent hyperadrenocorticism (PDH) and adrenal-dependent hyperadrenocorticism (ADH). This guide provides a comprehensive comparison of these two types, explaining their causes, diagnostic pathways, treatment strategies, and long-term outlook to help you understand what to expect. ## At a Glance: Pituitary vs. Adrenal Cushing's Disease The distinction between the two forms of Cushing's disease is crucial because it dictates the treatment approach and prognosis. The following table offers a rapid clinical comparison. | Feature | Pituitary-Dependent (PDH) | Adrenal-Dependent (ADH) | | :--- | :--- | :--- | | **Cause** | A benign tumor (adenoma) of the pituitary gland in the brain, leading to excess ACTH secretion. | A tumor (usually benign, sometimes malignant) of the adrenal gland, which directly produces excess cortisol. | | **Prevalence** | Accounts for approximately 80-85% of spontaneous cases. | Accounts for approximately 15-20% of spontaneous cases. | | **Typical Patient** | Small to medium breed dogs, often older (middle-aged to senior). | Larger breed dogs may have a higher risk, but any breed can be affected. | | **ACTH Stimulation Test** | Typically shows an exaggerated cortisol response. | Often shows a blunted or normal response to synthetic ACTH. | | **Low-Dose Dexamethasone Suppression (LDDS) Test** | Shows cortisol suppression at 8 hours in about 30-40% of cases. | Shows no suppression of cortisol at 8 hours. | | **Endogenous ACTH Level** | Normal to high. | Low to undetectable. | | **Ultrasound Findings** | Both adrenal glands appear symmetrically enlarged. | One adrenal gland has a visible mass; the other is often shrunken (atrophic). | | **Treatment** | Primarily medical management with drugs like trilostane or mitotane. | Surgical removal of the affected adrenal gland is the preferred option if the tumor is benign and resectable. Medical management is an alternative. | | **Prognosis** | Generally good with consistent medical management and monitoring. | Good for benign tumors that are surgically removed; guarded for malignant tumors. | ## Understanding the Anatomy and Physiology To understand Cushing's disease, you must first understand the endocrine axis that controls cortisol production. This is known as the hypothalamic-pituitary-adrenal (HPA) axis. 1. **The Hypothalamus:** This region of the brain releases corticotropin-releasing hormone (CRH). 2. **The Pituitary Gland:** Located at the base of the brain, this gland responds to CRH by secreting adrenocorticotropic hormone (ACTH) into the bloodstream. 3. **The Adrenal Glands:** These are two small glands, one located near each kidney. Each adrenal gland has an outer layer (cortex) and an inner layer (medulla). The cortex is stimulated by ACTH to produce and release cortisol. Cortisol is essential for life. It helps regulate metabolism, reduce inflammation, manage stress, and maintain blood pressure. In a healthy dog, cortisol levels are tightly regulated. When cortisol is high, the hypothalamus and pituitary reduce their stimulation, a process called negative feedback. In Cushing's disease, this regulatory system fails, leading to chronically elevated cortisol levels that cause the clinical signs of the disease. ## Causes and Differentials: The Two Main Types The vast majority of canine Cushing's disease cases are spontaneous, meaning they are not caused by external factors. The two primary forms are distinguished by where the abnormality lies. ### Pituitary-Dependent Hyperadrenocorticism (PDH) PDH is the most common form, accounting for about 80% to 85% of cases. It is caused by a functional tumor in the pituitary gland. In over 90% of cases, this tumor is a benign adenoma (a slow-growing, non-cancerous mass). This tumor produces excessive amounts of ACTH, which overstimulates both adrenal glands. The overstimulation causes them to enlarge (hyperplasia) and produce excessive cortisol, regardless of the body's needs. The cause of the pituitary tumor itself is generally unknown. ### Adrenal-Dependent Hyperadrenocorticism (ADH) ADH is less common, accounting for the remaining 15% to 20% of cases. It is caused by a tumor directly on one of the adrenal glands. This tumor autonomously produces cortisol, meaning it does not respond to the normal feedback mechanisms. In about half of the cases, this tumor is a benign adenoma. In the other half, it is a malignant carcinoma, which has a higher potential to spread (metastasize) to other parts of the body, such as the liver or lungs. Because the tumor produces cortisol on its own, the pituitary gland's production of ACTH is suppressed. This leads to atrophy (shrinking) of the opposite, healthy adrenal gland. ### Iatrogenic Cushing's Syndrome A third, less common cause is iatrogenic, which results from the prolonged or excessive use of corticosteroid medications (such as prednisone or dexamethasone) to treat other conditions like allergies or immune-mediated diseases. This form is not a spontaneous tumor but is a drug-induced side effect. Treatment involves a gradual, veterinarian-supervised tapering of the steroid medication. ## Risk Factors and Signalment While any dog can develop Cushing's disease, certain factors influence the risk. - **Age:** Cushing's disease is primarily a disease of middle-aged and older dogs. The average age at diagnosis is around 10 to 11 years. - **Breed:** Certain breeds are predisposed. Poodles, Dachshunds, Beagles, Boxers, Boston Terriers, and Yorkshire Terriers are commonly cited as having a higher risk for PDH. Larger breeds, such as the Labrador Retriever, may have a higher incidence of adrenal tumors. - **Sex:** Some studies suggest that female dogs may be slightly more predisposed to ADH, while PDH appears to affect males and females equally. It is important to remember that breed predisposition is a statistical observation, not a certainty. Any dog, including mixed breeds, can develop this condition. ## Clinical Signs: What an Owner Might See The clinical signs of Cushing's disease are primarily due to the catabolic (breaking down) and immunosuppressive effects of chronic cortisol excess. They are often subtle at first and can be mistaken for normal aging. The most common signs include: - **Polyuria and Polydipsia (PU/PD):** Increased thirst and increased urination are often the first and most noticeable signs. The dog may start having accidents in the house or need to go out more frequently at night. - **Polyphagia:** A significant increase in appetite. The dog may beg for food constantly or become more aggressive around food. - **Alopecia and Skin Changes:** Hair loss is common, often symmetrical on the trunk, sparing the head and legs. The skin may become thin, fragile, and darkly pigmented (hyperpigmentation). Dogs may also develop calcinosis cutis, where calcium deposits form hard plaques in the skin. - **Pot-Bellied Appearance:** The abdomen becomes distended and pendulous. This is due to a combination of weakened abdominal muscles, an enlarged liver (hepatomegaly), and redistribution of fat to the abdomen. - **Lethargy and Muscle Weakness:** Dogs may become tired easily, have difficulty climbing stairs or jumping onto furniture, and may show signs of muscle wasting, especially in the hind limbs. - **Panting:** Increased or excessive panting is common, even without exercise or heat. - **Recurrent Infections:** Due to immunosuppression, dogs may be more prone to skin, urinary tract, and respiratory infections. These infections may be slow to resolve with treatment. ## Veterinary Examination and Diagnostic Workup If you suspect your dog has Cushing's disease, a visit to your veterinarian is the first step. There is no single, perfect test. The diagnostic process is a stepwise approach. ### Step 1: Initial Assessment Your veterinarian will begin with a thorough physical examination and take a complete history. They will look for the classic clinical signs, such as a pot belly, hair loss, and muscle wasting. They will also recommend baseline blood and urine tests. A urinalysis is particularly important to check for a urinary tract infection and to assess urine concentration. A urine specific gravity that is dilute (below 1.020) is a key finding. Routine blood work often reveals elevations in liver enzymes (especially alkaline phosphatase, or ALP), cholesterol, and glucose. These findings are supportive but not diagnostic for Cushing's disease. ### Step 2: Confirmatory Testing If the initial tests and clinical signs are consistent with Cushing's disease, your veterinarian will recommend one of the following confirmatory tests. These tests are not used to differentiate between PDH and ADH; they are used to confirm that Cushing's disease is present. - **ACTH Stimulation Test:** This is a common first-line test. A blood sample is taken to measure the resting cortisol level. Then, a synthetic form of ACTH is injected, and another blood sample is taken one hour later. In a dog with Cushing's disease, the cortisol level will be excessively high after stimulation. This test is also the standard test used to monitor dogs on medical therapy. - **Low-Dose Dexamethasone Suppression (LDDS) Test:** This test is considered by many to be the gold standard for confirming Cushing's disease. A baseline cortisol level is measured. Then, a very small dose of dexamethasone (a synthetic steroid) is injected. Blood samples are taken at 4 hours and at 8 hours post-injection. In a normal dog, the dexamethasone will suppress cortisol production. In a dog with Cushing's disease, this suppression does not occur adequately. ### Step 3: Differentiating PDH from ADH Once a diagnosis of Cushing's disease is confirmed, the next critical step is to determine whether it is PDH or ADH. This distinction is essential for choosing the right treatment. - **Endogenous ACTH Concentration Test:** This test measures the level of ACTH in the blood. It is the most direct way to differentiate the two forms. In a dog with PDH, the pituitary tumor produces excess ACTH, so the blood level of ACTH is normal or high. In a dog with ADH, the adrenal tumor suppresses the pituitary gland, so the blood level of ACTH is low or undetectable. - **Abdominal Ultrasound:** An ultrasound is a non-invasive imaging technique that allows the veterinarian to visualize the adrenal glands. In PDH, both adrenal glands will typically appear symmetrically enlarged. In ADH, one adrenal gland will have a visible mass, and the other gland will often appear small and atrophic. An ultrasound can also help assess if an adrenal tumor has invaded the surrounding blood vessels (such as the caudal vena cava) or if there is evidence of metastasis to other organs. - **High-Dose Dexamethasone Suppression (HDDS) Test:** This test is used less frequently now with the availability of better imaging and the ACTH test. It is based on the principle that pituitary tumors are often partially suppressible by high doses of dexamethasone, while adrenal tumors are not. In about 60-70% of PDH cases, cortisol levels will suppress by more than 50% after a high dose of dexamethasone. This test is not perfect, as some PDH cases do not suppress, making it less reliable than the endogenous ACTH test. ## Evidence-Based Management and Treatment Options The goal of treatment is to control the clinical signs and reduce the risks associated with chronic cortisol excess, not necessarily to achieve a "normal" cortisol level. The treatment approach depends entirely on the type of Cushing's disease diagnosed. ### Medical Management for Pituitary-Dependent Hyperadrenocorticism Medical therapy is the mainstay of treatment for PDH. The two most commonly used drugs are trilostane and mitotane. - **Trilostane:** This drug works by inhibiting an enzyme (3-beta-hydroxysteroid dehydrogenase) involved in cortisol synthesis in the adrenal gland. It is currently the most widely used and preferred medication in veterinary medicine. It is generally well-tolerated, but requires careful monitoring. The goal is to find the lowest effective dose to control clinical signs while minimizing side effects. Regular ACTH stimulation tests are needed to ensure the dose is appropriate and to prevent over-suppression, which can lead to a condition resembling Addison's disease (hypoadrenocorticism). - **Mitotane:** This drug is an adrenocorticolytic agent, meaning it destroys the cortisol-producing layers of the adrenal cortex. It is an older drug that is also effective but has a higher risk of side effects and requires a more complex induction and maintenance protocol. It is used less frequently today, but may be a suitable option in some cases. **Monitoring:** Both drugs require lifelong treatment and regular veterinary check-ups. Owners should be educated on the signs of over-treatment (lethargy, vomiting, diarrhea, loss of appetite) and under-treatment (return of clinical signs). ### Surgical Management for Adrenal-Dependent Hyperadrenocorticism For ADH, the preferred treatment is surgical removal of the affected adrenal gland (adrenalectomy). This is a complex and delicate surgery that requires a skilled surgeon. - **Surgical Success:** The prognosis is good if the tumor is benign and can be completely removed. Surgery removes the source of excess cortisol, and the dog can often return to a normal life. - **Post-Operative Care:** After surgery, the remaining healthy adrenal gland is often atrophic and needs time to recover. The dog will typically require glucocorticoid and sometimes mineralocorticoid supplementation for weeks or months until the remaining gland regains its function. This is a critical period that requires close monitoring. - **Malignant Tumors:** If the tumor is a carcinoma, surgery is still the best option, but the prognosis is more guarded. There is a risk the cancer has already spread. In cases where surgery is not possible (e.g., due to invasion into major blood vessels or metastasis), medical management with trilostane or mitotane can be used to help control the clinical signs, though it will not cure the cancer. ### Radiation Therapy For PDH, radiation therapy targeting the pituitary tumor can be an option, especially for large tumors that are causing neurological signs. It is not widely available and can be expensive, but it can be effective in reducing tumor size and improving clinical signs. ## Unsafe Home Remedies and What to Avoid There are no proven, safe, or effective home remedies for Cushing's disease. The condition is caused by a tumor and requires veterinary intervention. You should avoid: - **Over-the-counter supplements:** No supplement has been scientifically proven to treat Cushing's disease. Some may interfere with diagnostic tests or prescribed medications. - **Human medications:** Never give your dog human medications for this condition. They are not formulated for canine use and can be toxic. - **Abruptly stopping medications:** If your dog is on trilostane or mitotane, never stop or change the dose without veterinary guidance. This can lead to a dangerous return of clinical signs or, conversely, an Addisonian crisis. - **Unsupervised dietary changes:** While a balanced, senior-appropriate diet is important, there is no specific "Cushing's diet" that can cure the disease. ## Prevention and Long-Term Prognosis There is no known way to prevent spontaneous Cushing's disease. The tumors that cause it are not preventable. The best an owner can do is to be observant for early signs and seek veterinary care promptly. The long-term prognosis for Cushing's disease is generally good, especially with early diagnosis and appropriate treatment. - **For PDH:** With proper medical management and monitoring, most dogs can live many more years with a good quality of life. Clinical signs like excessive thirst and urination often improve within days to weeks of starting treatment. Hair regrowth may take several months. - **For ADH:** The prognosis depends on the tumor's malignancy. Dogs with a benign tumor that is successfully removed can have an excellent prognosis and may not require long-term medication. Dogs with a malignant carcinoma have a more guarded prognosis, with survival times often dependent on the extent of the disease at diagnosis. ## Limitations and When to Contact a Veterinarian This article is educational and is not a substitute for veterinary diagnosis or treatment. The information provided here is a general overview, and individual cases can vary significantly. Breed-level information, such as the predisposition of Poodles or Boxers, is a statistical observation and cannot predict what will happen in your specific dog. Your dog's unique medical history, concurrent conditions, and response to therapy will shape their individual prognosis and treatment plan. You should contact your veterinarian immediately if you observe any of the following: - **Signs of a potential Addisonian crisis (over-treatment):** This includes sudden weakness, lethargy, vomiting, diarrhea, collapse, or a loss of appetite in a dog on medication. - **Worsening of clinical signs:** If your dog's drinking and urination do not improve, or if they get worse, the medication dose may need adjustment. - **New neurological signs:** If your dog develops seizures, head tilt, circling, or changes in behavior, this could indicate a large, expanding pituitary tumor ("macrotumor"). - **Difficulty breathing:** Excessive panting can be a sign of a pulmonary thromboembolism, a rare but serious complication. - **Any new or unusual symptoms:** Always err on the side of caution and consult your vet if you are concerned about your dog's health. ## Frequently Asked Questions ### What is the difference between pituitary and adrenal Cushing's disease in dogs? Pituitary-dependent hyperadrenocorticism (PDH) is caused by a benign tumor in the brain's pituitary gland that overproduces ACTH, stimulating the adrenal glands. Adrenal-dependent hyperadrenocorticism (ADH) is caused by a tumor on an adrenal gland that directly produces excess cortisol. ### How does a veterinarian test for Cushing's disease in dogs? Diagnosis is a two-step process. First, a confirmatory test like an ACTH stimulation test or a low-dose dexamethasone suppression (LDDS) test is used to confirm the disease. Then, to differentiate PDH from ADH, an endogenous ACTH test or an abdominal ultrasound is performed. ### What is the most common treatment for pituitary-dependent Cushing's disease? Medical management with oral medications is the standard treatment for PDH. Trilostane is the most commonly used drug, and it works by reducing cortisol production in the adrenal glands. ### Is surgery an option for treating Cushing's disease in dogs? Yes, surgery is the preferred treatment for adrenal-dependent Cushing's disease. It involves the surgical removal of the affected adrenal gland, which can be curative if the tumor is benign and has not spread. ### What are the common side effects of Cushing's disease treatment? The most significant risk of medical treatment is over-suppression of cortisol, leading to signs of Addison's disease, such as lethargy, vomiting, diarrhea, and poor appetite. Regular veterinary monitoring is essential to manage this risk. ### Can Cushing's disease in dogs be cured? Pituitary-dependent Cushing's disease is not curable but is manageable with lifelong medication. Adrenal-dependent Cushing's disease can be cured if the adrenal tumor is benign and successfully removed surgically. ### What are the early signs of Cushing's disease in dogs? The earliest and most common signs are a marked increase in thirst and urination, along with a significant increase in appetite. Owners may also notice lethargy and a reduced ability to exercise. ### How long can a dog live with Cushing's disease? With appropriate treatment and monitoring, many dogs with Cushing's disease can live for several more years with a good quality of life. The prognosis is generally better for PDH and for benign adrenal tumors that are surgically removed. ## Related Clinical & Scientific Guides * [Pancreatitis in Dogs: High-Fat Danger, Fluid Therapy and Bland Diets](/knowledge/veterinary-medicine/internal-medicine/pancreatitis-in-dogs-high-fat-danger-fluid-therapy-and-bland-diets) * [Dilated Cardiomyopathy DCM in Dogs: Diet-Related Taurine Gaps and Recovery](/knowledge/veterinary-medicine/internal-medicine/dilated-cardiomyopathy-dcm-in-dogs-diet-related-taurine-gaps-and-recovery) * [Addisons Disease in Dogs: Hypoadrenocorticism Crisis Electrolyte Balance](/knowledge/veterinary-medicine/internal-medicine/addisons-disease-in-dogs-hypoadrenocorticism-crisis-electrolyte-balance)