Despite being the doggie equivalent of 90 years of age, and despite being mostly blind due to cataracts, Brexit, an elderly shepherd mix, still manages to be a spry old girl and seems to enjoy life. A while back, however, her owner noticed some changes. “Brexy is drinking more water and urinating more,” she reported. “And she’s got a bit of a potbelly.” I was immediately concerned about common diseases consistent with these symptoms that we often see in older animals, such as kidney failure, or cancer of the liver or spleen. “Let’s run a few tests,” I suggested. Basic bloodwork and a few radiographs ruled out my initial worries. The only abnormality was elevation of an enzyme called alkaline phospatase, which, in a geriatric patient, can be completely normal. But this clue combined with her owner’s observations made me think the old dog might have hyperadrenocorticism (HAC), also known as Cushing’s disease.
HAC is a syndrome that typically affects older dogs, with females slightly overrepresented. Breeds predisposed to HAC include beagles, boxers, German shepherds, poodles, terriers, Dachshunds, and Labrador retrievers. Common symptoms may include excessive eating, drinking, and urination, excessive panting, abdominal distention, hair loss and poor regrowth, muscle weakness, lethargy, hyperpigmentation, and thinning of the skin, blackheads, urine leakage, and recurrent urinary tract and skin infections.
What actually causes all these troubles? A malfunction resulting in excessive production by the adrenal glands of the steroid hormone cortisol. Why do the adrenal glands malfunction? There are two different reasons. The most common is the presence of a benign, but hormone-secreting, tumor of the pituitary gland in the brain. This tumor secretes adrenocorticotropic hormone (ACTH). That’s a big word, but just means that this hormone stimulates the adrenal glands to produce cortisol.
Normally, the body has a “feedback loop,” so when a healthy pituitary gland recognizes that the adrenals have produced sufficient cortisol, it stops making ACTH. Without the signal from the pituitary, the adrenals then stop cortisol production. But in pituitary-dependent hyperadrenocorticism (PDH), the pituitary tumor just doesn’t know when to quit. It keeps pumping out ACTH, which keeps telling the adrenal glands to make more and more cortisol. The excessive cortisol results in all the aforementioned symptoms. PDH accounts for about 85 percent of all cases of canine Cushing’s disease. The second type of Cushing’s is adrenal tumor hyperadrenocorticism (ATH), caused by a malignant tumor right in the adrenal gland that continues making cortisol regardless of whether the pituitary is telling it to or not. ATH accounts for about 15 percent of HAC cases.
So I can just run a test and see if Brexit has HAC, right? Sorry, it’s not that simple. There are several different tests. Each has pros and cons. None is reliably definitive. I usually begin with the simplest, least expensive, and least invasive. “Can you bring me a urine specimen?” I asked. “It should be a morning sample collected when Brexy hasn’t been stressed.” Her mother agreed. Now stay with me here … all dogs with HAC spill cortisol in their urine. If the sample tested negative, i.e., no cortisol in the pee, then we could rule out Cushing’s and cross it off our list of differential diagnoses. But a positive result for urine cortisol does not unequivocally indicate that Brexy has Cushing’s disease. Why not? Because although normal dogs don’t usually have cortisol in their urine, occasionally they can, especially when stressed. A positive test increases our suspicion of HAC, but doesn’t definitively diagnose it.
Brexy’s urine was positive for cortisol. What now? To know for sure would require further endocrine testing, either an ACTH stimulation test or a low-dose dexamethasone suppression test (LDDS). OMG! So many initials! Don’t go to sleep! I’m not going to explain the tests. I’m going to explain why we opted not to do them.
HAC is a chronic illness. It can be hard to live with a dog who has an uncontrollable appetite and is urinating all over the house. Treatment is aimed at controlling symptoms, thus improving quality of life for both pet and owner. We do not cure the underlying pituitary or adrenal tumor. (In ATH cases, surgical excision of adrenal tumors may be attempted, but complication and mortality rates are high. The majority of HAC cases are PDH and treated medically. Surgical removal of pituitary tumors is not advised.) There are two different oral medications that can be used. One partially inhibits synthesis of cortisol, the other actually kills off a portion of the adrenal gland, thus reducing cortisol secretion. Treatment also reduces risk of secondary problems such as pancreatitis, diabetes, hypertension, and blood clots. On the other hand, treatment is lifelong, can cause side effects, and requires careful (and expensive) monitoring.
It can pose a bit of a dilemma for a veterinarian to decide what to recommend. To treat or not to treat? Just like human physicians, our first rule is “do no harm.” But unlike your doctor, we can’t ask our patient for input. We have to depend on you to observe your pet carefully and interpret behavior. In this case, Brexy’s symptoms are subtle and don’t seem to bother her. Visits from the veterinarian, however, stress her out, as do needles and blood draws, even when we do everything by house call. She also has a history of gastrointestinal upset, with many medications. Would the treatment be worse than the disease? And if we aren’t going to pursue treatment, does it make sense to pursue diagnostics?
For now, Brexit’s mom has opted not to go further. The old dog is remarkably agile and happy, considering her age and disabilities, and at this time, her clinical signs are barely perceptible. A less observant owner might not have even noticed. It her symptoms progress, we will revisit the decision and proceed with diagnostics and, if indicated, medication. But for now, we have all voted to leave things as they are, as long as Brexit seems content.