Understanding Cushing’s Disease in Dogs: Symptoms and Treatment

1. Introduction

Many pet owners are not familiar with the medical condition Cushing's. This potentially fatal condition is clinically known as "hyperadrenocorticism" and it impacts canines. The cause of Cushing's in dogs is typically a tumor on the pituitary, a gland in the body; however, it has also been found to be the result of an adrenal tumor. Regardless of the pathology, Cushing's affects dogs by flooding their body with excess cortisol, the hormone released when an animal is stressed. When too much of this stress hormone is present, it can lead to an array of health problems including the breakdown of bodily tissues. Muscles can be lost, leading to an overall weakening of the pet and a firmer appearance. The disease also weakens the immune system, so resistance to illness is reduced. Cushing's is treated best when caught early, which is why it is so vital for pet owners to recognize the signs of Cushing's as quickly as possible. In this post, we will explain Cushing's symptoms and ways it is treated.

Cushing’s disease, or hyperadrenocorticism, is a common hormonal disorder in middle-aged and senior dogs. This condition arises when a dog's body produces an excess of cortisol, the stress hormone, leading to noticeable behavioral changes and physical symptoms, such as increased panting, thirst, and appetite.

The pituitary and adrenal glands are central to Cushing's disease. The pituitary gland, a small pea-sized structure at the base of the brain, releases the adrenocorticotropic hormone (ACTH), which signals the adrenal glands (located above the kidneys) to produce cortisol. In a healthy dog, the adrenal glands regulate cortisol levels by signaling back to the pituitary when enough hormone has been produced. However, in dogs with Cushing’s disease, this feedback system malfunctions, resulting in continuous cortisol production even when it’s unnecessary.

There are two primary types of Cushing’s disease in dogs:

1. Pituitary-Dependent Cushing’s Disease : The most common form, caused by a benign growth on the pituitary gland. This mass produces hormones that continually stimulate the adrenal glands, causing both glands to enlarge. Diagnosis typically requires advanced imaging, like a CT scan or MRI, to detect the pituitary mass.

2. Adrenal-Dependent Cushing’s Disease : Caused by a growth on one of the adrenal glands, which may be benign or malignant. This type results in an overproduction of cortisol by the affected gland while the other remains normal. Diagnostic methods include abdominal ultrasound or CT scans.

While cortisol plays essential roles in immunity and the “fight or flight” response, excessive levels in Cushing’s disease disrupt hormonal balance, resulting in various symptoms. Most often, this condition arises from a benign pituitary tumor that constantly signals for cortisol production, but it may also stem from adrenal tumors or prolonged steroid treatment for other health issues. Cushing’s disease primarily affects dogs over the age of 7, highlighting the importance of monitoring older pets for signs of this condition.

Why should common dog owners know about Cushing's today? The disease has been covered in extensive amounts of research, so treatment is relatively easier to come by now. It is not always curable, especially if the disease has advanced, but it can be treated and even lead to remission. The right treatment decisions need to be made, however, so early recognition of symptoms is helpful. Pet owners should know about Cushing's disease and what the symptoms look like because Cushing's is health-damaging, although it is not always noticeable quickly and does not produce obvious symptoms. Recognizing Cushing's allows for quicker treatments, which leads to better long-term outcomes. Current pet owners should review this section carefully to recognize if their dog is showing signs of Cushing's disease. Cushing's signs are often explained but not placed into a large category, allowing for specific symptoms to remain unseen. This is why we have written this post for you today.

2. Causes and Risk Factors

Cushing's disease in dogs can develop from primary sources, which are internal as well as external reasons. The internal cause originates from either benign or malignant tumors that increase the volume of either the pituitary gland or the adrenal gland, or both. Due to the increase in gland size, the tumor stimulates its host gland to increase cortisol production per unit volume. This continuous production of cortisol exceeds the hypothalamus' capacity to produce negative feedback regulation, leading to continuous ACTH as well. The continuous production of ACTH stimulates the increased cortisol-producing gland, which indefinitely stimulates cortisol production. Iatrogenic Cushing's can also be triggered by steroid hormones from external sources. Recognizing these sources and risk factors may be very effective in preventing this disease. Various dog breeds can be prone to pituitary-dependent Cushing's, as can some older dogs and some environmental factors such as fertility disorders and obesity.

In general, the classification of etiological factors or causes is divided into two, namely endogenous and exogenous. The division of these causes is essential for prognosis and therapeutic strategies in both pets and human medicine. In the case of pets, complaints are given from clinical research to the public, in this case, dog owners. The underlying causes of Cushing's disease, endogenous and exogenous, can be significant to explain to the dog owner in the hope of increasing their awareness, so that they are more careful in giving certain medications in the future. This can avoid misperceptions in the public that Cushing's disease is only caused by excessive corticosteroid medications if given only therapeutic doses. To convince and educate, we also need clinical findings and screening of diagnostic visuals to provide clarity to the public about the size of the gland.

Cushing's disease in dogs is most commonly caused by a slow-growing, benign tumor on the pituitary gland that stimulates excessive cortisol production. Less frequently, a mass on the adrenal gland—either benign or cancerous—may also trigger the disease by overproducing cortisol. Additionally, long-term use of corticosteroids, like prednisone, to treat conditions such as allergies or autoimmune issues, can lead to iatrogenic Cushing's, where the medication itself induces symptoms rather than a tumor. This type of Cushing’s is often reversible under veterinary guidance once the medication is stopped. Certain breeds, such as Poodles, Yorkshire Terriers, and Dachshunds, have a genetic predisposition to Cushing’s disease. Identifying the underlying cause of Cushing’s is essential for effective treatment, as each type has its own prognosis.

2.1. Endogenous vs. Exogenous Causes

The dog does not have health insurance that pays for tests on a regular basis, so he rarely makes visits to the vet. Furthermore, in busy households or those with lots of dogs, subtle changes in a dog’s weight or drinking and urination habits may be hard to discern. Subtle signs of Cushing’s disease can be mistaken for age-related changes in the dog quickly. Lack of treatment of symptoms can lead to life-threatening conditions such as diabetes or pyometra.

Exogenous causes are associated with owner behavior, typically involving the use of synthetic corticosteroid medications causing Cushing’s disease to develop. Endogenous causes involve the internal parts of the dog’s body, leading to changes in the endocrine system. This can involve pituitary tumors, which account for approximately 80% of confirmed Cushing’s cases in dogs. This condition can cause excessive ACTH production by the pituitary, leading to abnormal growth and function of the adrenal gland. If there is a link, the resulting high plasma cortisone concentration can interact with the brain to prevent more ACTH production. Because the rest of the adrenal tissue is not affected, when the tumors are removed, the dog normalizes its hormone levels, and the disease is cured, or at least the dog may go long periods of time without the need for medication.

3. Symptoms and Clinical Signs

A telltale sign of Cushing’s disease is increased water intake and increased urination. Owners often remark that their dogs are drinking from the toilet or their water bowl and urinating so excessively during the night that they are constantly having to let them out to the bathroom as if they were puppies again. Owners may also discover their dogs urinating in the house. These symptoms can develop gradually and sometimes may be overlooked, especially if there is a backyard or a dog flap. Affected dogs are often ravenously hungry and will maneuver their owners into giving them more food by whining and carrying on as if they are starving. All of this extra food does not go unnoticed, and these dogs can rapidly gain weight and have a change in their body shape. Many dogs develop a fat or pot-bellied appearance with muscle wasting in the body and appearance of the leg muscles known as panting easily. Wanting to eat more, drinking more, and large potbellies are the hallmarks of Cushing’s disease, and a few breeds can develop proteinuric kidney disease. The skin begins to thin, and most dogs experience hair loss of varying degrees, such as just around their face or on both sides of their bodies, down their spines, or around their tails. Hair loss is often the first thing the owner observes in cats with Cushing’s disease.

Since the adrenal glands secrete many types of hormones, dogs can experience changes in their reproductive system. Female dogs usually stop having their heats altogether, while males can have testicular enlargement, infertility, or reduced libido. The immune system can get suppressed, and pets will get sick more often. The clinical signs may be classic, mild, or absent. In some cases, because these dogs drink so much, they may also develop too much water consumption, and the symptoms of a subclinical Cushing's dog are that of the other condition. Deciphering between a subclinical Cushing's dog and one with only diabetes or only hypothyroidism can also make it difficult, as both diabetes and hypothyroidism can lead to hair loss and mental dullness. Slow metabolism with descriptions such as lazy or lethargic lying on the furniture are often also part of the descriptions of the symptoms of Cushing’s. More advanced Cushing's dogs can be really sluggish and slow to respond and really fat dogs that just lay there and certainly do not feel like going for a walk. Brachycephalic breeds—the ones with the pushed-in faces that are really heavyset usually feel this way. These dogs tend to be really nice and cuddly dogs who do not want to miss their naps in the sun. Histories are often for years, and the owners have no idea why these dogs are sickly and overweight, as just going outside can be an effort, also because walking is not much fun since Cushing's dogs are often panting due to no energy reserves. This is a tough thing for the owners to cope with because they miss the exercise and stimulation that their walks once provided. It is also difficult for vets to have these discussions with owners, as many clients become very defensive of their pets. In a Great Dane, however, the clinical signs may consist of significant weight loss and a pot belly.

3.1. Physical Symptoms

When dogs develop Cushing’s disease, they often display a variety of physical symptoms that concerned owners may notice. While panting is common in many dogs, dogs with Cushing’s can pant excessively. In many dogs, owners often express concern about increased panting and loss of muscle mass. They may also notice that their dog is gaining weight, even without a change in diet or activity level, due to a redistribution of fat stores. With Cushing’s, fat will often accumulate along your dog’s neck and abdomen, creating the appearance of a “pot belly.” This can often cause concern in owners who cannot understand how their dog can be losing muscle mass but gaining weight. When owners do feel areas of the dog’s body, they may often describe them as thin or greasy, depending on the nature of the dog’s skin changes.

In addition to changes in body shape, dogs may develop other signs related to their skin and coat changes. Specifically, increased fat stores will often lead to changes in the dog’s coat. Not only will the hair’s texture change, but dogs may also lose large patches of fur. These patches have been described as “splotchy” or “moth-eaten.” In chronic cases, where the dog has had the disease for a longer period, these patches may never grow back. Their coat may also develop brown skin staining. This may either occur as darkening around the armpits or as brown crusts along the dog’s lower back. Other dogs develop skin infections which can result in extreme itchiness or have oily skin. Ultimately, all of these signs are usually related to the high amount of cortisol present and how it can affect a dog’s overall health. Depending on how long your dog has had Cushing’s and how severe the signs appear, your pet may look very healthy, may keep getting sick, or some combination depending on the day. If you have seen any of these signs, make an appointment with your vet to get your dog checked out! Help keep an eye out for these symptoms and clarify why a dog has a certain appearance. It is important to understand the underlying nature of the disease, the hormones involved, and the symptoms that may result, both in the dog’s appearance and behavior. This will often aid in distinguishing another disease condition from Cushing’s disease.

3.2. Behavioral Changes

Behavioral changes in dogs that suffer from hyperadrenocorticism (HAC) can offer critical insights for veterinarians and owners to rescue a pet. Increased lethargy and a noticeable decrease in activity levels, sometimes accompanied by an increase in food and water consumption, can be noticeable changes for devoted pet owners. Sometimes changes in your beloved pet are not as apparent to the pet owner's eye. Changes such as increased anxiety or other changes in temperament, such as irritability or mood swings, can affect a pet as well as a pet owner. These shifts in behavior often stem from the discomfort and health issues that are initiated from excessive cortisol production. Changes in behavior are especially helpful in early diagnosis. Behavioral changes offer a unique opportunity to evaluate the quality of life of a pet. Excessive thirst as well as drinking and urinating habits are sometimes not noticed by pet parents, but instead they take notice of their pets who are adhering to the water bowl more than usual. Since pets are usually taken out for their daily walks, the increased urination can be difficult to monitor. Subsequently, observations on an increase in facial swelling as well as the presence or history of urinary incontinence can give essential life history information to the veterinarian. All these subtle changes can initiate a discussion with a veterinarian regarding the need to monitor and eventually test for potential underlying health issues. Thus, early detection can have a very significant impact on a pet's current condition and future overall health. Behaviors are the sum of the animal as a whole, of both body and mind, and if a pet parent notices anything out of the ordinary, they should talk to their veterinarian.

4. Diagnosis and Diagnostic Tests

Diagnosing Cushing’s disease (also known as hyperadrenocorticism) is not always a straightforward affair. A veterinarian might suspect Cushing’s based upon the relevant background of the dog he is examining, together with the physical symptoms displayed – but that only gains a diagnosis if it has been confirmed by various tests. It’s also essential, not just for proper treatment of the dog but also for the well-being of the rest of the family concerned. There are several diagnostic tests for Cushing’s disease; none is foolproof, but most veterinarians prefer to use a combination of two or three to create as thorough an impression of what is happening in a dog’s body as they can. Diagnosis of Cushing’s involves first very thorough history-taking and physical examination. Blood tests are the most common type of diagnostics used, including what is known as a “biochemical profile” as well as hormone tests for cortisol and adrenocorticotropic hormone. A procedure that is also useful is to check cortisol levels in the urine. As a “stress hormone,” the cortisol level in a dog’s body fluctuates. An imbalanced or irregular pattern of cortisol fluctuations can signify underlying health problems. Once an initial positive is confirmed, an adrenocorticotropic hormone stimulation test is the most common method used to establish if the pituitary or adrenal gland is the root of the problem. Rarely, but available, a special blood test is used to look at so-called “low-dose” dexamethasone suppression or the extended dexamethasone suppression test. Imagery, generally in the form of an ultrasound or X-ray, might be used when testing for atypical Cushing’s, mostly a tale of tumors prominently in the abdominal area. To eliminate that possibility, a vet may suggest image examination of the adrenal glands or even all chest and abdominal regions which may be affected.

4.1. Blood Tests

4.2. Urine Tests

Urine tests complement blood tests in the diagnosis of Cushing’s disease. These tests can be used to help determine whether a dog has Cushing’s disease, which form of the disease is present, and the best way to manage that dog. The urine cortisol-to-creatinine ratio measures the amount of cortisol present in the urine compared with the creatinine concentration. Creatinine is produced by the body at a relatively constant rate and is eliminated from the body at a constant rate via the kidneys, while cortisol levels can fluctuate. This test can help to determine whether cortisol output is normal, higher than normal, or below normal in a dog. Typically, the urine cortisol-to-creatinine ratio is high in dogs with overproduction of cortisol; in contrast, it is usually in the lower or middle of the normal range in dogs with diseases other than Cushing’s disease. For dogs receiving trilostane, when monitoring for disease control, the urine cortisol-to-creatinine ratio can be used to double-check whether the hormone levels are truly reduced to the desired range.

Urine concentration is also assessed to check for urinary tract infections or to evaluate urinary concentrating ability or water excretion for kidney function, which can be impaired in dogs with Cushing’s disease. As for the urine cortisol-to-creatinine ratio, defects in urine quality can also impact test results, even for urine concentration tests. In general, tests to evaluate urine concentration are not as sensitive or specific as blood tests to diagnose Cushing’s disease, and their results should be combined with the results of blood tests and the characteristic clinical signs observed. They are, however, generally easy for veterinary practices to perform, and so can be helpful for initial screening and monitoring purposes.

5. Treatment Options

The treatment options for Cushing’s disease will depend on the cause of the condition and the severity of the clinical signs that are seen. The benefits and possible negative effects of the available medical treatments and the decision to proceed with treatment will be made based on a multitude of clinical factors and the needs of the individual pet. a. Medical Management The best way to minimize the clinical signs of Cushing’s disease is by decreasing the amount of cortisol that the body produces. The most common way of doing this is by using medications that affect the adrenal glands and/or the pituitary gland. The first plan of action is usually the use of medications like trilostane, which reduces cortisol production from the adrenal glands. If damage to the adrenal glands leads to a decrease in cortisol production, a medication like prednisone may be needed for the remaining life of the dog. There are also medications that can kill some of the adrenal tissue that is overproducing cortisol; these medications will be used to reduce the size of adrenal tumors. Following the reduction of the adrenal tumors, the remainder of the adrenal tissue is allowed to recover so that the dog can stop taking cortisol-replacement medications. Mitotane is the drug most commonly used for this purpose. b. Surgical Management If the cause of Cushing’s disease is an adrenal tumor, surgical removal of the affected adrenal gland may cure the condition. The decision to perform this surgery will be based on a multitude of clinical factors, including the health status of the dog, a thorough evaluation of the cancerous potential of the tumor, and the dog’s overall individual needs. Regardless of the choice of medical or surgical treatment, every dog must be carefully monitored for a varied amount of time, with numerous adjustments possibly being necessary in either the pet’s medications or clinical monitoring plan.

5.1. Medication

Treating Your Pet Beyond the Stereotype: What and Why to Tell Your Clients with Cushing’s Disease

5.1. Medication Long-term medication is a crucial part of managing both PDH and ACTH disease. The goal is to reduce the overproduction of hormones by direct inhibition or destruction of the relevant cells. Pharmacologically, we can intervene in three parts of the post-endocrine cell secretory process: synthesis, storage, or release. With PDH, the most effective and convenient medical intervention is to reduce the production of cortisol either by interdicting synthesis through the adrenal steroidogenic pathway or by causing necrosis of the adrenal corticotrophic cells through the administration of mitotane. Hyperadrenocorticism of any form exacerbates such an insulin-resistant state, with treated dogs often gaining weight, making many owners anxious for an early return to 'normal' hormonal function. Outside of the charitable or research context, this is more a preference for a healthier pet dynamic than one for a healthier pet. While some owners truly struggle, or if there are untenable financial constraints, we can aim for less lush control than the mechanism. Owners who feel empowered by understanding and tailoring their own pet’s hormonal status should perceive 'success' as an ability to stay out of the danger zones highlighted in this article.

Surgical success and efficacy for either type of Cushing’s can wane or 'burn out.' We must tailor our early and regular clinical pharmacokinetic testing to try and hit each pet’s nadir cortisol levels roughly in the mid-third of their reference range. This gives us the best results in terms of perceived quality of life and incidence of adverse effects. It allows us to 'borrow time' between clinical rechecks and buying increasingly toxic drugs and/or sudden hospitalization. This coordination of strategy and tailor-made pharmacology using natural physiology also gives an owner a greater sense of control. Trilostane is a capsule that fits into a gel-like structure designed to protect the drug so it only releases its contents in the small intestine, outside the stomach. Ensure owners understand the importance of this as a human overdose can be fatal. Ensure compliance, administer with breakfast, and ask about missed doses in advance. Formulations 'in-house' removing the gelatine from the original capsule to give one-quarter or fifth doses for light, small breed, or borderline cases are safe as long as the entire drug mass is swallowed, but certainly less accurate than the licensed crushed tablet options. Ensure vomiting is advised with availability for a clinical examination and repeat administration within 1 hour by a competent adult. Measure urinary specific gravity, and dose reduction is also a good idea in the first 2 days post-chemotherapy dose. It is also advisable to measure the adrenocortical autoantibody activity annually as drug-resistant conditions can sometimes exhibit early.

5.2. Surgical Intervention

Severe complications can cause heart failure, liver failure, life-threatening infections, and profound weakness due to the destruction of the dog's muscle, which is known as spleen laceration. Endoscopic treatment may not be possible in these severe cases. Adrenalectomy can be performed in dogs with an adrenal tumor if the clinical signs are compatible with Cushing's disease, the adrenal lesion is unilateral, and there is no other illness affecting the dog. The brain and both adrenal glands must be examined before surgery. No sex, age, or breed is more likely to have a benign or malignant tumor than another. Benign tumors are more common in dogs with Cushing's disease from an adrenal tumor. Prognosis is generally considered good to excellent if the disease has been present for less than a year and owners are compliant with follow-up tests. Making a decision about the best option to treat Cushing's disease can be very challenging for many pet owners. Surgical intervention to remove the source of the disease is a powerful treatment once the right tumor type and location in the dog are identified. Surgical intervention is the treatment of choice in dogs that have a pheochromocytoma or an adrenocortical tumor if their clinical signs are severe. Other conditions that might be causing the clinical signs must be addressed successfully if surgery is to be considered, and not all dogs are good candidates. Surgery on the adrenal gland is not a failure when medical therapy has been considered first in a dog that has an adrenal gland tumor with no malignancy possible, no tumor mass in the liver or lungs, and a dog that has not lived with the clinical signs of Cushing's disease for a long term, i.e., 1 year or less.

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