Visiting Veterinarian : Shadow's story
Almost weekly I get a call about some big ol' dog having trouble with his hind end. Reports range from the succinct "Flopsy can't get up" to the histrionic "Mopsy has collapsed!" These calls are often at 6 am...at that hour I have trouble getting up too. Typically the patient is a large breed, often overweight, who has gotten himself onto a slippery surface, like linoleum or hardwood flooring. After lying around all night, his back hurts. Or his hips. Or his knees. Or all of the above. "Put him on a rubber-backed rug where he can get traction," I advise. "Use a towel as a sling around his belly to hoist him up, then position his feet squarely underneath him." Once up and moving around, most of these dogs are fine, although often in need of arthritis medication.
So when Shadow arrived with a history of "trouble with stairs and getting into the car," I stifled a yawn and prepared my usual spiel. After all, this 90-pound, 10-year-old lab cross was a poster pup for being prone to orthopedic problems. I watched him walk from the car. All four legs worked normally. No definitive limp. Maybe a hint of weakness as he climbed the porch stairs.
Once he was on the table I examined him inch by inch. "He seems a bit painful here," I observed, palpating his lower back. Shadow resisted manipulation of his legs, but everything moved properly, nothing else seemed to hurt. His right hip clicked when rotated...but so does mine. Nothing impressive. "Let's run a quick test to rule out Lyme and the like," I suggested. Eight minutes later I stared ruefully at the results. Negative for Lyme but positive for antibodies to both Ehrlichia and Anaplasma.
"There's a good chance Shadow is not actually infected," I explained. "Odds are he just has antibodies from previous exposure, but we should send out confirmatory tests to be sure." I sent him home on doxycycline to cover for tick-borne disease until our tests came back, and pain medication, still confidant that he was simply an old, achy dog.
The next morning Shadow's mom called again. Shadow was not better. In fact, he was worse. "He's not eating and can't get up at all." "Where is he?" I asked, watching patients fill my waiting room. "The kitchen," she replied. Ah, that slippery linoleum. "Listen, you have to give the medication time to work," I said, impatiently. My receptionist waved an urgent message from another client in my face. "Doxycycline sometimes makes them queasy. That may be putting him off breakfast."
My daughter, home sick from school, shouted "I need tea!" while Shadow's mom rattled off a stream of explicit details about his condition. "I hafta go," I interrupted curtly. "I have clients waiting. Come in for a recheck if you want, but if I were you, I'd give it another day." Hanging up the phone, I put on the kettle, dealt with the message, and waded into a sea of appointments.
Hours later, coming up for air, I collapsed at my desk and perused Shadow's record. I had been rude to his owner. Not the first time I've lost my composure on a hectic day. Shrugging sheepishly at my foibles, I called her back. "I want to apologize for this morning," I began.
"That's okay," she responded generously, "but I really am worried." Wanting to reassure her, I suggested they come right over, although deep down I suspected she was overreacting.
Wrong again. Shadow arrived. Helping him out of the car, he crumpled in the parking lot, unable to stand. I placed his feet squarely on the ground, but all four legs knuckled over, then buckled beneath him. Something was drastically wrong. "Get the stretcher," I called. We carried Shadow inside. The slight hind end weakness noted yesterday had gotten dramatically worse and was now affecting the front legs too, a condition technically called tetraparesis. There was a long, scary list of possible causes. Spinal cord tumor, tick paralysis, intervertebral disc disease, botulism, idiopathic polyradiculoneuropathy.
Shadow was going to need a lot of tests, and a lot of nursing care. "We could do radiographs and blood work here," I offered "but I think he should see a neurologist ASAP." His owners agreed. Shadow's symptoms had progressed so rapidly we were all leery of what might happen next.
That evening Shadow went to a specialty clinic off-Island. Radiographs and ultrasound revealed a small mass in his chest. Could this be causing his weakness? Well, maybe. If this mass was a tumor of the thymus gland, then Shadow might have a syndrome called paraneoplastic myasthenia gravis. Let me explain.
Myasthenia gravis (MG) is caused by a malfunction in transmission of information between nerves and muscles. Normal transmission involves nerves secreting acetylcholine and muscles responding via specialized receptors. In congenital MG, animals are born with abnormal receptors. Symptoms of weakness are apparent by eight weeks old. More common is acquired MG, an adult-onset immune-mediated disease, in which the body spontaneously makes antibodies against its own receptors. A third form is paraneoplastic MG, which appears to be induced by the presence of certain tumors such as a thymoma or osteosarcoma.
Mild cases of MG present as trouble swallowing, regurgitation of food (due to esophageal muscle dysfunction), voice change, and weakness after exercise. More severe cases may present with acute collapse, aspiration pneumonia due to poor gag reflexes, and death from respiratory muscle failure. Definitive diagnosis is done by testing for acetylcholine receptor antibodies. Since this can take days for results, Shadow's specialist made a rapid presumptive diagnosis using a "Tensilon test." The physiology and pharmacology are complicated, but the main idea is that an injection of this drug will cause obvious, albeit brief, improvement in dogs with MG. Shadow improved dramatically, leading the doctors to conclude that the mass was probably a thymoma, and Shadow had paraneoplastic myasthenia gravis.
Shadow is now being treated with appropriate long-term medication. He has flown south for the winter. Doctors there will address the thymoma. Prognosis ranges from guarded to good, depending on how completely they can resect his tumor. And I got a good reminder to listen closely to my clients, because, despite the old medical adage "if you hear hoof beats, don't look for zebras," every now and then, it's a zebra.
