Canine Cushing's Syndrome - Diagnosis and Treatment

When a dog's body produces too much of the hormone cortisol, it can lead to an endocrine disease known as Cushing's syndrome, also called hyperadrenocorticism.

In this SoyUnPerro article, we'll explain what it involves, covering its most common causes and symptoms, especially in some dog breeds more genetically prone to this dysfunction. We'll also talk about how it's diagnosed and the main treatment for Cushing's syndrome. This way, you'll better understand how it's managed.

Why does canine Cushing's syndrome occur?

As mentioned, Cushing's syndrome is linked to cortisol, a hormone that, at proper levels, helps the body respond well to stress, regulate metabolism (which is directly tied to weight), and maintain healthy skin and coat, among other things.

However, when there's ongoing overproduction of cortisol, the dog's immune system weakens, leaving them more exposed to infections and other diseases. It can also cause changes in certain organs and the skin, compromising the dog's health.

The causes of Cushing's syndrome can vary, though three main factors can be identified:

1. An abnormal function of the pituitary gland, which regulates the activity of most endocrine glands. This accounts for 80-85% of Cushing's syndrome cases, and is known as PDH ("Pituitary-dependent hyperadrenocorticism"). It's usually due to hyperplasia (enlargement) or a tumor of this gland.
2. An abnormal function of the adrenal glands, where cortisol is produced. This accounts for the remaining 10-15% of cases.
3. An idiopathic cause — that is, a reaction caused by certain medications used to treat other conditions in dogs.

Cushing's syndrome is considered a chronic endocrine condition that can cause serious changes in our pet's body, so it's important to catch it as early as possible in order to start treatment.

Symptoms of Cushing's syndrome in dogs

The most common clinical signs shown by a dog with Cushing's syndrome are as follows:

• Polydipsia (increased water intake) and polyuria (more frequent urination).
• Polyphagia (hungrier than usual).
• Skin changes — that is, coat or skin problems (including hair loss).
• Apathy and lethargy — appearing more tired than usual.
• Muscle weakness or wasting.
• Pot-bellied abdomen — a characteristic sign of this disease.
• In females, there can be disruptions to the reproductive cycle.
• In males, testicular atrophy can occur.
• Behavioral changes can appear.

There are also other signs that can point to a dog having this syndrome. That said, it's often detected because of another secondary condition caused by Cushing's, mainly canine diabetes, hypothyroidism, or other endocrine disorders. In fact, around 10% of cats with Cushing's syndrome develop diabetes, with the figure reaching up to 80% in cats.

Because these symptoms are so nonspecific, they're often attributed to a dog simply getting older, so the syndrome can go unnoticed at first. This can make early diagnosis harder, which is key for the dog to regain their health.

Symptoms usually appear progressively and can even take a few years to show up all together, which also makes diagnosis harder. What's more, not every dog responds the same way to elevated cortisol, so symptoms can vary case by case.

Which dogs are more prone to Cushing's syndrome?

Dogs most commonly affected by Cushing's syndrome are older dogs (from around 6 years of age), as well as animals dealing with stress.

Sex and breed are factors that influence the development of this condition. Females develop the disease up to 3 times more often than males. As for breeds, the most prone are the Dachshund, Poodle, Boston Terrier, Miniature Schnauzer, Maltese, and Old English Sheepdog. Among large breeds, the most common cause tends to be adrenal gland tumors.

How can we know for sure if a dog has this disease? Let's take a look.

Diagnosis and treatment of Cushing's syndrome

To diagnose Cushing's syndrome in our dog, the vet will need to do an exam and take a history, along with a series of additional diagnostic tests, including the following:

• Blood test: a stress leukogram is characteristic, with an abnormal white blood cell count — these are the cells responsible for immune function.
• Chemistry panel: this lets us measure cortisol levels and other biomarkers that help diagnose the disease (ALT, blood glucose, cholesterol...).
• Urine test: increased urine density and an abnormal urine cortisol-to-creatinine ratio help confirm the diagnosis.
• Imaging diagnosis (X-ray, ultrasound, CT scan, MRI): this lets us assess the size and appearance of the organs involved in this disease (the pituitary and adrenal glands).
• ACTH (adrenocorticotropic hormone) suppression test: a low dose of a corticosteroid (dexamethasone) is given to assess ACTH levels and see whether the pituitary's production of this hormone is affected.

In short, a full workup will be needed to find out what's affecting our furry friend. The goal is to confirm the diagnosis and determine the cause (whether pituitary or adrenal in origin), and give treatment suited to each type, whether medical or surgical.

If Cushing's syndrome is iatrogenic (caused by medications that raise cortisol levels), that medication schedule will need to be stopped or changed. Either way, it's very important for a dog with this condition to attend regular check-ups with the specialist, to monitor their cortisol levels and adjust medication as needed.

Although Cushing's syndrome is a serious disease that usually shortens our pet's life expectancy, if we manage to diagnose it early and start proper treatment in time, we can improve our pet's prognosis and greatly help their quality of life.

Bibliography: https://www.msdvetmanual.com/endocrine-system/the-pituitary-gland/cushing-disease-pituitary-dependent-hyperadrenocorticism-in-animals?query=cushing https://www.msdvetmanual.com/endocrine-system/the-adrenal-glands/cushing-syndrome-hyperadrenocorticism https://www.fda.gov/consumers/articulos-en-espanol/como-tratar-la-enfermedad-de-cushing-en-los-perros