Big Ben was a 10-year-old neutered male golden retriever who Mom and Dad had noticed was drinking more for the past few weeks. His family veterinarian had run some laboratory tests to try and figure out why, and found an elevated calcium level.
To normalize his drinking, we had to figure out why the calcium was elevated. Excessive thirst and urination are not the only problem that occurs when calcium is elevated. More significantly, if left high for too long, it will cause permanent kidney damage, formation of urinary bladder stones and mineralization in other areas of the body.
The body has a system in place to tightly regulate calcium levels to prevent problems. At the center of this is the parathyroid gland. These are tiny glands that sit on top of the thyroid glands in the neck. They produce parathyroid hormone (PTH) that along with vitamin D help regulate blood calcium levels.
So the first test I (Perry Jameson) ran in Big Ben was a parathyroid level. Sometimes in older dogs they will develop a benign parathyroid tumor that is so small you cannot feel it, yet it produces too much hormone. This extra parathyroid hormone causes the calcium to elevate. Treatment is to surgically remove the gland or inject the gland with ethanol to kill it.
Usually just one of the glands is involved, but the problem is that the remaining normal glands have shut down production and it may take days to weeks for them to wake up again. Most dogs will need a potent form of vitamin D as well as calcium supplements for several weeks until the dormant glands start to make PTH again.
Big Ben’s PTH level was low, ruling out hyperparathyroidism. Another test for Addison’s disease, where the adrenal glands do not make enough of their hormones, also came back normal.
Kidney failure also can result in a calcium elevation, but blood testing showed no signs of it.
Vitamin D exposure can cause calcium elevations as well. This is not the same vitamin D in milk or that you buy over the counter; these are much more potent forms found in medications or rat poisons. But that too was normal.
The problem I began to worry about most with Big Ben was cancer. Certain cancers will produce a parathyroid-like protein that the body responds to in the same way it does real PTH, a calcium elevation. Blood was submitted for this parathyroid-related protein and it came back elevated.
Many cancers will do this but the most common ones are lymphoma, multiple myeloma and anal sac tumors. During exams, I could not feel any enlarged lymph nodes or anal sac masses. Also, blood tests showed no evidence of leukemia (a type of lymphoma) or multiple myeloma (detected as high proteins). I looked for cancer on chest X-rays and abdominal ultrasound but could find none.
In dogs where I cannot find cancer but suspect it, they usually have lymphoma hidden somewhere. I talked to Mom and Dad about further options, including giving Big Ben a dose of a chemotherapy agent that usually puts lymphoma in remission and will lower the calcium if that is the cause.
They elected to try the therapy, and within days Big Ben’s calcium normalized and his thirst and urination returned to normal. He was treated by the oncologist for lymphoma and remained in remission for the next two years, feeling great the entire time.
Cats can develop hypercalcemia for many of the same reasons but the most common cause in the feline is idiopathic hypercalcemia. That is a fancy way of saying we do not know the reason. When testing does not provide me with an answer, this is what I suspect them to have.
Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to firstname.lastname@example.org.