Using the CBC to Diagnose Seizures?
There was an interesting paper that was published in the spring of 2026 that didn’t get a lot of attention at the time. However, I found the findings intriguing, if not quite clinically useful yet. Read on and enjoy!
This study was published in the Journal of Veterinary Internal Medicine (JVIM) by Dr. Wang and colleagues. Their goal was to determine if a routine CBC had any markers that could be used to distinguish idiopathic epilepsy from other forms of seizures.
Results
· 181 dogs were enrolled: 55 healthy (no seizure history), 126 with neurologic disease
· Of the 126 with neurologic disease: 46 dogs with idiopathic epilepsy (IE), 24 with hydrocephalus, 39 with MUE and 17 with brain tumors
· Their diagnosis of IE was rigorous. All dogs needed to have normal labs, normal brain MRI and normal CSF tap.
· The most interesting finding was that the platelet-lymphocyte ratio (PLR)was substantially lower in dogs with idiopathic epilepsy compared to dogs with any structural form of epilepsy.
What does this mean?
The researchers divided the platelet value by the lymphocytes to get the ratio. For example: platelet count of 300,000 divided by a lymphocyte count of 2000 = 150. See the table below for the median PLR. We don’t need a PLR to distinguish between a healthy dog and a dog with seizures but we could use an easy test to help distinguish a dog with idiopathic epilepsy from a dog with structural brain disease, right? This is where it gets interesting. The median PLR for IE is 132.3, and the median PLR for structural epilepsy (hydrocephalus, brain tumor) was 240.3. The difference between the two was significant (p=0.0004). With a cut off of 178.3, there was a sensitivity of 84.8% and specificity of 78.1% with AUC of 0.85. This is pretty good diagnostic accuracy. Not perfect, no, but very very interesting!
The authors noted that the PLR was very good at detecting dogs with brain tumors (cut off 178.3, sensitivity 84.3% and specificity 90.9%) but there were only 11 dogs so I don’t think I’d take that to the bank just yet.
Group
Median PLR
Healthy
94.9
Idiopathic epilepsy
132.3
Hydrocephalus
164.0
MUE
240.8
Brain tumor
246.5
How does this work? In this study, the authors note that dogs with IE and structural epilepsy had higher than normal platelet counts and lower than normal lymphocyte counts. This suggests that there is change in systemic neuroinflammatory activity. Platelets can be a part of the inflammatory signaling pathways and lymphocytes might migrate through the BBB during an inflammatory process. Importantly, PLR might demonstrate association but does not dictate the mechanism! Remember that lymphocytes and platelets are also affected by many non-seizure related causes, too. Stress, systemic inflammation or infection, systemic neoplasia, physiology, platelet disorders and concurrent illness to name a few.
One last interesting fact. Dogs with IE that were controlled with one AED had a higher PLR than those that required second or third AED. This feels counterintuitive to me! More inflammation should equal more difficulty controlling the disease, right? Apparently, the authors speculate that more inflammation may make the dogs MORE responsive to treatment!
The take home message
Next time you have a dog with new onset seizures, check the CBC and perform a PLR. See what you get. If the value is greater than 178, perhaps this is supportive of a structural brain disease. If it is less than 178 perhaps this is idiopathic epilepsy. How does this value change over time? Does it change? Again, neurologic examination, MRI and CSF tap are still the gold standard for diagnosing intracranial diseases so please do not rely on a CBC as the sole diagnostic tool. But, with some practice, this tool might become a non-invasive way to help us determine the best course of action for a given patient.
Thanks for reading! I hope you have a great rest of your week. I will be off October 13-20th (and likely we won’t have a TidBit) so please be patient with email and telephone responses. I am taking some time off to celebrate a milestone birthday for a kid!
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