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Narrowing down the possibilities

October 17, 2021 at 4:00 a.m.

When I examine a sick patient, I immediately begin to sort through lists stored in my mind of possible causes for their symptoms. Some cases are easier to sort through than others. Diagnostic testing then helps me to narrow down the possibilities. Occasionally, I am surprised by what we find, and in other instances, I must treat for the most likely disease process and monitor for improvement. It can be frustrating to be unable to put a name on the cause for my patients' illnesses, but knowing their response to treatment can help me to rule in or rule out the remaining possible causes (called differentials).

Elliott is one of those patients with a surprising outcome that we haven't quite put a name on just yet. He is a precious, 8-year-old, small mixed-breed dog. I first saw Elliott for concerns about red spots on his skin. On that day, I treated him conservatively for an allergic reaction. He appeared healthy otherwise. A few days later, Elliott returned for a swollen ear flap (ear pinna). On exam, this swelling appeared fluid-filled. I immediately knew that Elliott had an aural hematoma.

An aural hematoma is a blood-filled swelling of the ear flap, similar to a large blood blister. This type of hematoma most often occurs as an animal shakes their head excessively or violently in response to itching or pain. The usual suspect is an ear infection, but every now and then, we find a hematoma without an ear infection. In Elliott's case, I didn't find an ear infection as the cause of his symptoms. We continued Elliott's exam.

The original red spots on his skin had resolved, but I did find a small bruise on his tummy. I noted that as a symptom. It wasn't likely that Elliott had experienced an injury or trauma, so I "scrolled down" my differential list to include toxin exposure, blood clotting disorder, autoimmune disease, infection, etc.

Next, I found that Elliott had a fever -- 103.2 degrees. A dog's normal temperature ranges from 100-101 typically, but a one-degree variation is not unusual. In a clinic setting, with a nervous animal, I allow their reading to extend up to 102.5 without concern, as long as they have no other concerning symptoms. As I added this symptom, my differential list ruled out toxin exposure (especially with no known history of this), and we could likely rule out a blood clotting disorder. So, my main concerns were narrowed to autoimmune disease or infection. We needed a blood count.

A complete blood count (CBC) measures the number of circulating white blood cells, red blood cells, and platelets. It gives information about those cells, including average size, the cell type's percentage compared to the total circulating cells, and more. In Elliott's case, he showed a mild anemia, and a mild increase in white blood cells. There are other ways to classify these findings, but that gets pretty boring to some people, so I will leave it at that for this discussion!

So, to recap, we have Elliott, an indoor, mid-aged neutered male dog. His symptoms include fever, bruising, and aural hematoma. And just a few days ago, he had skin redness that responded to treatment. The main differentials remaining are autoimmune disease or infection. The most likely type of infection that would cause this level of fever and anemia for dogs is tick-borne infection.

When I look at those two possibilities, it can be difficult to determine with certainty which is causing Elliott's disease without further testing. These tests are accessible by sending samples out to a reference lab, but we needed to do something right now to help Elliott. I had to treat him right away without a final answer. Based on past experience, I am most suspicious of tick-borne infection.

To help Elliott right away, I drained the blood from his ear pinna and infused a steroid solution to help limit inflammation and refilling of the blood. I also prescribed Doxycycline (an antibiotic used to treat tick-borne infection), and Prednisone (a steroid that will be useful in treating both a tick-borne infection and the aural hematoma). If Elliott does in fact have a tick-borne infection, this treatment will be successful. If he has an autoimmune disease, the medications can still be helpful, but the steroid would need to be given at a higher dose.

Elliott is scheduled to return in one week to repeat his exam and blood work. If his condition worsens in any way, he will come back sooner. If he and his blood work are improving, then our top differential of tick-borne infection was likely the right call. Further testing for tick-borne infection and/or autoimmune disorder is available. Elliott's case is an example of how we, as veterinarians, work to help our patients right away, when all of the information isn't immediately available.

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