Immune mediated meningoencephalitis (aka meningitis of unknown origin: MUO) is very common and is a cause of intracranial disease for many pets. Infectious meningoencephalitis accounts for only about 2% of the cases seen through a referral center and is, therefore, in the minority. Infectious meningitis may be secondary to fungal infection, protozoal (Toxoplasma or Neospora), viral, bacterial or in southern states, some tick borne diseases. Neospora infection is one of the more common causes of infectious meningoencephalitis we see in Wisconsin (probably second only to fungal) and therefore one of the main differential diagnoses for a pet with meningoencephalitis. The current way to diagnose Neospora is via serum titer elevation, evidence of encysted protozoa on biopsy or necropsy, or PCR on serum or CSF. All of these tests take a variable amount of time, depending on the laboratory, so some researchers in the UK came up with another idea. (https://onlinelibrary.wiley.com/doi/epdf/10.1111/jvim.16334)
Scientific Question: Can we differentiate between Protozoal meningoencephalitis and MUO using CK and AST values?
Rational: Protozoa (Toxoplasma and Neospora) are often found in muscle which would result in membrane disruption, thus elevating CK (and subsequently AST). Seizures, a common sign of MUO and protozoal meningoencephalitis, can also elevate CK so the researchers also aimed to evaluate the temporal relationship between seizures and CK elevation.
Methods: This was a retrospective study of 59 dogs diagnosed with MUO and 21 dogs diagnosed with Neospora (no dogs were diagnosed with Toxoplasma in this study).
Results: A significantly higher CK and AST value were identified in dogs with Neospora compared to those with MUO. Using a cutoff value of 458 U/L, there was a sensitivity of 95.24% and specificity of 96.61% for active Neospora meningoencephalitis and using a prevalence of 2.25% for active infection in the UK, there was a negative predictive value of 99%. This suggests that dogs with a CK less than 485 U/L are unlikely to have a diagnosis of Neospora infection associated with their intracranial signs. Twenty of 21 dogs with Neospora had CK higher than 485 U/L, and 2 dogs with MUO had CK > than 485 U/L in this study.
Things to remember: CK has a short half-life (22 hours) so if you test, do so within the acute phase of disease. CK and AST are not muscle specific and can be found in myocardium, intestine and AST in the liver also.
What do you do with this information? If you have a dog with suspected meningoencephalitis, consider running a CK and AST on initial blood work. If it is greater than 485 U/L, a Neospora titer should be performed.
Have a great week and thanks for reading!
Note about the holidays: I will be available for emergency cases on December 24, and 25th.
New Years Eve and Day, I will be spending time with my family building a colossal gingerbread house and stables. If I'm not baking, cutting and cooling gingerbread I will be making sticky frosting glue and won't be available for phone calls, texts or email. Thank you for your understanding!