Hormone imbalance may lead to Cushing’s disease in dogs

Currer, an older dachshund, had gotten tangled up in a rope and hurt her foot, but that wasn’t her only complaint. There was a big bald patch on her back, the surrounding fur caked with odd, whitish debris. “That started when the cat scratched her,” Currer’s mom said.

I tugged gently on a tuft. The whole wad peeled away, leaving an even larger naked spot. I shook my head. “Doesn’t look like something from an injury,” I said, gazing thoughtfully at my patient. She was swaybacked — a concave arch in her upper back, an upward hunch in the lower. Her belly was plump and round, almost distended, though nothing abnormal noted on palpation. “Let’s treat that foot, plus antibiotics and medicated shampoo for the skin infection,” I suggested. “We’ll see how it goes.” We talked more about dachshunds, their propensity for back problems, and the need to get Currer’s weight down. Then I sent them on their way.

Though the limp improved, Currer soon returned. Not sure which things were significant, her owner provided me with a list of woes. “I think the glands in her neck were bigger, though not anymore,” she said. A mass that had been present in the anal area for many years had recently gotten larger, then drained some fluid, and returned to how it had looked previously. One time Currer cried when she tried to open her mouth. The dog was drinking and urinating more than normally, and having accidents in the house.

“TMI!” my brain protested, reeling with diagnostic possibilities. “We need to run some tests,” I said aloud, preparing to draw blood. A few hours later, lab work in hand, I had a suspicion of which symptoms were relevant and what might be wrong.

Hyperadrenocorticism (HAC), also known as Cushing’s disease, is a disorder caused by the ill effects of long-term excessive cortisol. Why does Currer have too much cortisol in her body? The most common reason is a benign pituitary tumor, which, although usually not malignant, does secrete a hormone called ACTH. That’s adrenocorticotropic hormone.

Don’t be scared by the big words. The concept is pretty simple. The pituitary gland in the brain is supposed to tell the adrenal glands, which sit in the belly alongside the kidneys, how much cortisol to produce. In a normal dog, when cortisol reaches the proper levels, the pituitary is happy and stops producing ACTH. The adrenal glands get the message and stop making cortisol. In HAC, that tiny pituitary tumor just doesn’t have an “off” switch. It keeps pumping out ACTH, pushing the poor adrenal glands to keep pumping out cortisol. This scenario accounts for about 85 percent of HAC cases. The remaining 15 percent are caused by tumors right in the adrenal glands, about half of which are malignant.

Regardless of the source, cortisol overload affects many different systems. The severity and specific signs depend on many factors and can vary greatly, case to case. Most dogs exhibit excessive drinking and urination. They are often inordinately hungry. The cortisol affects muscle tone and fat distribution, leading to a pot-bellied appearance. Other signs can include enlarged liver, hair loss, lethargy, muscle weakness, obesity, muscle atrophy, pimples, panting, incontinence, facial nerve paralysis, and a variety of skin disorders including thin, wrinkled skin, poor healing, and hair loss. HAC is common in dogs. Poodles, dachshunds, Boston terriers, boxers, schnauzers, and beagles are particularly prone. Most affected dogs are middle-aged or older, though it can occasionally be seen in younger animals.

Currer fit the picture. An older dachshund. Drinking and peeing excessively. Pot-bellied appearance. Skin problems. Our initial blood work also gave us a few clues that we were headed in the right direction, specifically a dramatically elevated enzyme called alkaline phosphotase. So we had our diagnosis, right? Not so fast.

Definitive diagnosis of HAC can be both challenging and expensive. First we tested Currer’s urine. It was unusually dilute, supporting the owner’s observation of excessive drinking and urination. A urine cortisol creatinine ratio found cortisol in Currer’s urine, another piece of data consistent with HAC, but still not definitive. There are two main tests veterinarians use for HAC, low dose dexamethasone suppression test or ACTH stimulation test. Sometimes both. I’ll spare you the details but simply say that by measuring how the adrenal glands and/or pituitary respond to administration of certain substances, we can usually confirm our diagnosis. Sometimes these tests also help distinguish whether the cause is pituitary tumor versus adrenal gland tumor, but often imaging techniques like ultrasound or even MRI are indicated to differentiate these two possibilities.

Several kinds of treatment are available for pituitary-dependent HAC. Lysodren and Trilostane are both drugs given orally. Lysodren selectively kills off part of the adrenal glands, thus lowering cortisol production. Trilostane inhibits an enzyme involved in cortisol synthesis. Both drugs must be given under close supervision with frequent monitoring, as they can occasionally create the opposite situation, a disorder called hypoadrenocorticism or Addison’s disease, which can be rapidly fatal. Since neither drug eliminates the pituitary tumor, lifelong therapy is required. Other medications sometimes tried include an antifungal drug called ketaconazole that interferes with cortisol production and an MAO-inhibitor called selegiline, or L-deprenyl, which suppresses ACTH production in the pituitary. Treatment for the adrenal form of HAC may be surgical, or medical, depending on the tumor, whether it is benign or malignant, and if it has spread. The prognosis for the adrenal form is usually much worse than for the pituitary-dependent form.

We sometimes opt not to treat HAC until symptoms are severe enough to cause obvious issues for either dog or owner. We are still deciding how to proceed with Currer. At 13 years old, we have to factor in the cost of all these diagnostics, medications, and monitoring, to think about possible side effects, and consider whether treatment will improve the quality of life for both her and her mom. Her symptoms are clearly progressing, but, at least today, she is still spunky and enjoying life.