Visiting Veterinarian : Animal instincts
Bobcat, the 12-year-old chocolate lab, has had his share of troubles. At the tender age of two he developed seizures and was diagnosed with idiopathic epilepsy. At three, he gave us a scare by downing a couple of sandwiches wrapped in Saran Wrap. Luckily, the plastic passed without incident. Over the next few years Bob had an ear hematoma, a benign growth on his eye, and a malignant tumor on his leg. One time he started having seizures that wouldn't stop until we intervened with emergency intravenous anticonvulsants. As a senior, Bob became arthritic and developed hypothyroidism, requiring daily thyroid supplements and frequent pain medication. When his owner noticed Bob was eating more but losing weight, pacing at night, and panting excessively, she initially ascribed it to his thyroid pills.
"I think the dose is too high," she told me over the phone. We decided to lower the dose of thyroid supplements and see if he improved. Several months later he arrived for his annual physical examination. Ten pounds lighter than in his younger days, and still panting heavily much of the time, his mother sighed. "He's just aged dramatically recently. Reducing his thyroid pills hasn't made a difference." Now plenty of old dogs pant, or get frail with advancing age, without this indicating anything dire, but it's good to listen to a mother's intuition. "Let's do some tests," I suggested, not overly concerned but wanting to reassure both of us. His mom agreed readily to X-rays and a battery of tests.
"His heart and lungs look fine," I pronounced when the films were done. There were a few changes consistent with aging (vets just call 'em "old dog lungs") but nothing worrisome. His heavy breathing sounded like a common condition in older, large-breed dogs called laryngeal paralysis, annoying but rarely life-threatening. Pacing at night is also common in elderly dogs, not unlike the restless insomnia older humans sometimes experience. The causes of "geriatric nighttime anxiety," as this syndrome is called, may range from pain, to emotional upset, to cognitive dysfunction syndrome, i.e., senility.
We had one more concern. Bob tested positive for antibodies to Anaplasma, a common tick-borne disease on the Vineyard. Many Island dogs have these antibodies. This doesn't necessarily mean they have the disease. In fact, in asymptomatic positive dogs, current research suggests less than five percent may be truly infected. But was Bobcat asymptomatic? Classic anaplasmosis presents with fever, lethargy, enlarged lymph nodes, and poor appetite. Bob didn't exactly fit this profile, but neither was he the picture of health. We sent out an additional test to definitively rule out Anaplasma infection. "Go home, don't worry," I said, walking his mom to the door, still confident that Bobcat's problems were probably not too serious. "I'll touch base when we have the lab results." Two hours later I sat at my desk, my head in my hands. Now I was worried. Bob was anemic. His white blood cell count was too low, as was his platelet count, the cells that help with clotting. His serum protein levels were high . . . really high. There were only a few things that were likely to cause this combination of test results. Anaplasma infection was one of them. Our test for that was pending. The other was multiple myeloma (MM), a malignant cancer of a type of blood cell called a plasma cell.
Definitive diagnosis of MM is based on documenting at least two of the following four criteria: monoclonal gammopathy, lytic bone lesions, Bence-Jones proteinuria, and abnormal bone marrow. Stay with me. I'll explain these, one at a time, starting with monoclonal gammopathy. Normal plasma cells make proteins called immunoglobulins (also known as antibodies or gammaglobulins) to fight infectious disease. In MM, cancerous plasma cells proliferate abnormally, producing excessive amounts of immunoglobulin, even though there is no infection to provoke this. Since immunoglobulins are proteins, one of the first clues is an elevated serum blood protein. Bobcat's was sky high. How do we know if all this protein is abnormal immunoglobulins or just an appropriate response to an infection? With infectious disease, plasma cells produce a range of different immunoglobulins, known as a polyclonal gammopathy. "Poly" means multiple or many, like a polygon has many angles, or a polygamist many spouses. Cancerous plasma cells stem from a single line and produce a single type of immunoglobulin, hence the name monoclonal gammopathy. "Mono" means single or one, like monogamy or monotonous . . . or monopoly, which uses both to mean "one owning many." A test called serum protein electrophoresis separates out the various immunoglobulins and determines if the protein elevation is monoclonal or polyclonal. What about lytic bone lesions? In MM, cancerous cells may start to eat away at the bones giving them a mottled, moth-eaten appearance on X-rays. I reexamined Bobcat's films and took an additional one. Nope, no bone lesions. Looking for very specific, unusual type of protein, called Bence-Jones, in Bob's urine was our next step. We sent a urine sample to the lab and waited.
Results trickled in. Negative for Anaplasma infection. Negative for Bence-Jones protein in his urine. Positive for monoclonal gammopathy, confirming one criterium. We needed one more to establish a diagnosis. In MM, cancerous plasma cells invade the bone marrow, crowding out the healthy tissue. Bob's unusually low blood cell counts were suspicious for abnormal bone marrow, but we couldn't advise chemotherapy without confirmation. Taking a bone marrow sample requires a certain amount of finesse. Since Bobcat was at risk for clotting problems, and we wanted to get the oncologists in on his case, we referred him to my favorite cancer specialists near Boston. They took a bone marrow sample, and did abdominal ultrasound and splenic aspirate. One day shy of one month after he walked in for his annual exam, the oncologists confirmed that Bobcat had multiple myeloma and started chemotherapy. The good news is the protocol is all oral medication so we can manage most of it right here at home. We changed his arthritis medication to one compatible with his chemo, and started him back on thyroid supplements. If all goes well, he has a good chance for a lengthy remission thanks to his mother's intuition and fast action, which resulted in an early diagnosis.
