When do you consider repeating CSF studies in a patient with suspected viral encephalitis but overall initially unrevealing CSF?  

Definitely not an expert on this topic, but this situation does come up, particularly for HSV encephalitis! One question worth asking your lab is what kind of assay are they using to run this test. If it's a dedicated HSV PCR assay (e.g., Simplexa), then the sensitivity is going to be quite robust,...