Adrenal Gland Disorders: Cushing's & Addison's Disease by Trevor Miller, DVM

Does your veterinarian seem preoccupied with your pet's bathroom habits?  How often have you been asked, “Any change in Bella’s thirst or urination?” during an appointment? Picking up poop and cleaning the litter box may not be your favorite aspect of pet ownership, but changes in an animal's elimination habits can give us a lot of information regarding potential internal medicine disorders.

Increases in thirst, and frequency of urination, can be particularly telling. Several hormonal diseases can result in a profound increase in urination.  Two such diseases involve the adrenal glands (two small glands nestled against the abdominal wall near the kidneys).  The adrenals are responsible for making a variety of hormones, which have broad reaching effects around the body.

One of the most potent and influential of the adrenal hormones is cortisol. If you've ever been through a stressful period in your life and found yourself having an increased appetite and a craving for fatty foods, you've felt the effects of cortisol. In addition to stimulating appetite, cortisol has a variety of effects, designed to help deal with life’s various stressors.

Some of the most common and useful medications in your veterinarian’s arsenal are also derived from cortisol, and are used to treat a great variety of conditions.

If not properly regulated cortisol levels can become chronically elevated, leading to a disease called Cushing's, or chronically depressed, leading to a disease called Addison's. Both are named for the 19th century physicians who first described the conditions in people. In our pet population these diseases are commonly found in dogs, but rarely so in cats.

Cushing’s disease, or hyperadrenocorticism, is the overproduction of cortisol, and can result from a glandular disorder in the brain or in the adrenal glands themselves. Dogs with this condition classically have increased thirst, urination, and appetite. Due to metabolic changes in the body, affected dogs can also develop a potbellied appearance, muscle weakness, hair loss, and skin infections.

Addison’s disease, or hypoadrenocorticism, is the underproduction of cortisol. This condition most often results from destruction of the adrenal glands by the animal’s own immune system. Along with a deficiency of cortisol, dogs often also lack in Aldosterone, a hormone responsible for the regulation of electrolytes by the kidneys. The symptoms created by Addison’s disease are notoriously vague and unpredictable, and for this reason it can be difficult to identify. Many dogs will experience waxing/waning stomach upset (vomiting and diarrhea), increased thirst and urination, weight loss, weakness, and muscle twitching. Dogs with this condition are unable to physiologically respond to stress, so these signs are often precipitated by stressful events.

Dogs with hypoadrenocorticism can also fall victim to what’s known as an “Addisonian crisis.”  The lack of the above hormones can result in rapid dehydration, electrolyte imbalances, low blood pressure, collapse, and potentially death.

Diagnosis of both Cushing’s and Addison’s ultimately involves hormonal testing and the measurement of cortisol levels. Clues to the presence of the diseases can also be gleaned from routine blood work, urinalysis, and direct visualization of the adrenal glands via an ultrasound exam.

Treatment for these conditions depends a lot on the underlying cause, but in a nutshell the goal is to restore hormone levels to their proper, physiologic ranges. If cortisol is being overproduced (i.e. Cushing’s), levels are reduced by surgically removal of the affected gland, or with medications that block the production of cortisol. If cortisol, and/or aldosterone, is being under produced (i.e. Addison’s), they are simply supplemented. 

The goal of treatment is very straightforward, but long term management of the diseases can be difficult and adjustments to the medications are generally necessary before balance, and normal urination, is restored.
 

Dr. Miller is a graduate of the Veterinary School at the University of California, Davis. Prior to veterinary school he received his undergraduate degree in Environmental Science from the University of California Berkeley. Originally from Placerville, CA, he grew up in the country surrounded by lots of animals. Dr. Miller has worked extensively with Fix Our Ferals and did a one year rotating internship at East Bay Veterinary Specialists and Emergency. He has an orange tabby cat named Gonzo and Quigley, a Lab mix. Dr. Miller loves skiing, traveling, reading, and racquetball in his spare time. He is also, of course, a huge Cal fan!

Tags: cushing's, addison's, adrenal glands, kidneys, pet health