Cushing’s Disease, which is common is dogs, is unfortunately very tricky to diagnose and is often discovered through a mix of symptom assessments and blood tests. There are three types of Cushing’s disease, two of them caused by glandular tumors, which in turn cause the adrenal glands to overproduce the hormone coritsol, which regulates various metabolic processes. Signs are many and varied and include excessive drinking, excessive urination, panting, poor muscle tone, a pot belly, thinning of the skin, and the prevalence of typically minor infections. Treatments range from medications to removal of the affected gland.
Hyperadrenocorticism or Cushing’s disease, also known as Cushing’s syndrome, is a common endocrine disease of middle-aged dogs responsible for a wide variety of symptoms associated with increased secretion of the hormone cortisol from the adrenal glands.
With Cushing’s disease, dogs’ adrenal glands will produce too much cortisol either because of a tumor in the brain’s pituitary gland (which stimulates the adrenal gland’s cortisol-producing tissue) or, less commonly, a tumor in the adrenal gland itself.
In the former case, the disease may go by the name “pituitary gland adenoma,” a nod to the benign type of tumor most commonly responsible for Cushing’s, or as “adrenal gland hyperplasia” by way of describing the brain tumor’s effect on the pituitary. In the latter case, Cushing’s can be referred to by the kind of tumor less commonly responsible for the disease: “adrenocortical tumor.”
A third type of Cushing’s disease is “iatrogenic Cushing’s disease” or “iatrogenic hyperadrenocorticism.” This occurs when dogs or cats have been exposed to quantities of cortisol-like steroids over time, therefore eliciting the same symptoms as naturally occurring Cushing’s. That isn’t being covered in this articles.
Though a direct connection to inheritance has not been established, it’s widely suspected that a genetic predisposition to Cushing’s disease exists due to the prevalence of the disease in certain breeds.
Signs and Identification
As previously mentioned, a wide array of symptoms can be attributed to the excess of cortisol in the body. Excessive drinking, urination, muscle wasting, a pot-bellied appearance, a thinning of the skin, the prevalence of typically minor infections.
Unfortunately, most symptoms of Cushing’s are nonspecifically related to abnormal fat and protein metabolism, the immune system, and inflammatory processes. This often makes for an insidious onset, difficult identification, and delayed diagnosis relative to other diseases.
Diagnosis is usually made based on screening tests that suggest the possibility of excess cortisol secretion. Confirmation is achieved through one or two challenge tests that measure the secretion of cortisol once injectable hormones are supplied. Measuring cortisol is not an effective enough approach, given the hormone’s fluctuating presence in the bloodstream. That’s why ACTH stimulation and low-dose Dexamethasone challenge tests are used. These tests may also be used to discriminate between the two types of Cushing’s.
Ultrasonography is also strongly recommended to help ensure that no tumor is visible (generally on one of the two adrenal gland), thus altering the choice of treatments available.
Cushing’s is more prevalent in the Poodle, Dachshund, German Shepherd, and terriers such as Yorkies and Dandie Dinmonts. The boxer, Boston Terrier, Labrador Retriever, Australian Shepherd, Maltese, and Cocker Spaniel may also be predisposed. Again, the mode of inheritance is unknown.
Treatment can be divided into two camps: medical and surgical. For both basic types of Cushing’s disease (brain tumor or adrenal tumor), both medical and surgical options are available.
For pituitary-dependent hyperadrenocorticism, medical treatment is typically undertaken with one of two common medications. Hypophysectomy (removing the pituitary), however, is a surgical option that’s becoming more widely undertaken as a one-time procedure that may trump side-effect-fraught medical therapy.
For the adrenal tumor variety, medical therapy for the pituitary-dependent version is available, but a complete cure may be effected by removing the affected adrenal gland surgically (adrenalectomy). The contralateral adrenal is generally perfectly normal in these cases.