Visiting Vet: Pandora’s box

Cats can present with symptoms that aren’t easy to track down.

Diagnosing pet problems sometimes opens up a Pandora's box. — Pixabay

Like many pets we see on an emergency basis during the summer, Pandora is a seasonal resident. A sweet 3-year-old cat, she eschews cold Vineyard winters, spending the off-season in sunny Mexico instead. When she arrived at my office recently with a history of sudden onset of episodes of yowling, drooling, and acting lethargic, which then progressed to full-blown seizures, I had a long differential diagnosis list. Toxins, infectious disease, trauma, cancer, metabolic illness, epilepsy. Were there other things to consider? Diseases not typically seen here, but perhaps common south of the border?

“Is she current on her rabies vaccination?” I asked. With any case exhibiting unexplained neurological signs, we must consider rabies, especially since the virus can be passed to people via the saliva of an infected animal, and the disease is almost always fatal. On the Vineyard, rabies has only been documented in a few bats, and Mexico has done an impressive job of controlling the disease there, but it still had to be on my list. Her owner assured me Pandora was vaccinated, and promised to provide documentation.

I advised drawing blood for a variety of tests, but, no, there is no blood test to determine if a live animal has active rabies. Definitive rabies diagnosis requires euthanizing the pet in question. No one wants to have to do this, so we needed to be extraordinarily careful that neither my assistant nor I got bitten. Pandora was as loving as could be, purring, rubbing up against us when we patted her … until we tried to take blood. I’m pretty adept at handling cats, but Pandora was adamant. Even oral tranquilizers didn’t make her more cooperative, and I was concerned too much stress might precipitate a seizure. Ultimately, we anesthetized her briefly to draw blood for a battery of tests.

Pandora went home on anticonvulsant medication, with instructions to keep her strictly confined while we collected information bit by bit. First we ruled out feline leukemia and feline immunodeficiency virus. Although these infections don’t typically cause seizures, they could predispose to cancer, including brain tumors. Next we ran a “4DX” test. This is designed for diagnosing heartworm, Lyme, ehrlichia and/or anaplasma in dogs. Although not approved for use in cats, many vets feel it is useful for felines as well. Pandora tested negative for the first three diseases, but showed a positive result for antibodies to anaplasma.

Hmmm. Was this the answer we were looking for? Anaplasmosis is a tick-borne disease common on the Island. There are several types, and yes, cats can get it … but anaplasmosis doesn’t usually cause seizures. Pandora showed none of the signs typically associated, such as fever and loss of appetite. We had already sent blood to the big reference laboratory for tests we are unable to do in-house. “Let’s add a PCR tick panel,” I suggested to her owner. This would confirm or rule out whether Pandora was truly infected with anaplasma.

The next results to come in were basic health screenings. Chemistry profile was normal, ruling out things like low blood sugar, liver, or kidney disease. Complete blood count, normal. No anemia. No abnormalities in any cellular components of her blood. Next came infectious diseases. Toxoplasma? This protozoal parasite, which commonly affects cats, can sometimes go to the brain and cause seizures. But Pandora tested negative for toxoplasmosis. The lab did find antibodies to feline coronavirus (nothing to do with COVID-19; don’t go there), but lots of healthy cats have these antibodies, and there is no easy way to assess if this is significant.

When her rabies documents arrived, I found that there had been a long gap between her first and second vaccine — longer than generally recommended. With her behavioral changes, drooling, and seizures, did we still need to consider rabies? I decided to call in the troops, consulting several specialists. Neurologists and internists weighed in. Relax about rabies, they said. Very unlikely. Then the toxicologist piped up. What about lead poisoning?

Plumbism is the technical term for lead toxicosis. It is more common in dogs than cats, simply because felines are more discriminating about what they eat, but cats may be exposed via lead-containing paint chips or dust, especially during home repairs or renovations; or they may occasionally ingest lead shot in the bodies of prey animals. Young cats are particularly susceptible. Clinical signs may be gastrointestinal or neurological, including vomiting, poor appetite, lethargy, hypersalivation, and seizures. I phoned her owner again. “Let’s call the lab and add a blood lead level.”

By the time all the tests were finished, we could rule out rabies simply because Pandora was still alive. Once clinical signs appear, rabid animals almost always die within 10 days. Pandora, however, was improving. So what was the final diagnosis? Lead levels were normal, so not plumbism … but the tick panel yielded an embarrassment of riches. Pandora tested confirmed positive for three different organisms — anaplasma, bartonella, and mycoplasma. Bartonella is the bacteria that causes “cat scratch fever.” Many cats carry it without any symptoms. In fact, infection rarely causes illness beyond a transient fever. Still, in some clinical studies, bartonella infection was occasionally associated with neurological signs. Mycoplasma is a funny little organism that comes in many varieties, but the species for which Pandora tested positive is considered relatively nonpathogenic, and found in many perfectly healthy cats. Finally, anaplasma has not been associated with seizures.

We started Pandora on two antibiotics to treat the anaplasma, bartonella, and mycoplasma. Without referral to a neurologist for cerebral spinal fluid tap and MRI, it is impossible to know if any of these organisms were responsible for her seizures, or if Pandora simply has epilepsy, and these infections are unrelated. Cats can have idiopathic epilepsy, i.e. seizures with no identified cause, or structural epilepsy related to congenital malformations. For now, we are closing this Pandora’s Box of laboratory tests, keeping her on anticonvulsant medication, and hoping she will continue to improve with our current course of treatment.