Author Response: CSF Biomarkers in Patients With COVID-19 and Neurologic Symptoms: A Case Series

We thank Dr. Brenner for his interest in our report1 and for emphasizing CSF neopterin results. Indeed, marked CSF immune activation indicating microglial activation is a universal feature in all patients with neurologic manifestations that we have examined in our clinic during the acute phase of COVID-19. Of interest, other typical signs of CNS infections-CSF pleocytosis, blood-brain barrier injury, and intrathecal IgG synthesis-are usually mild or absent, and viral RNA is almost never detected. These features clearly distinguish COVID-19 from typical CNS-invasive infections but are similar to processes seen in other CNS encephalitides2 and, as suggested, may well resemble influenza-encephalitis that is also a consequence of a respiratory viral infection.

Automated summary

In patients with neurological manifestations of COVID-19 during the acute phase, marked CSF immune activation indicating microglial activation is a universal feature, while other typical signs of CNS infections are usually mild or absent. These features distinguish COVID-19 from typical CNS-invasive infections but are similar to processes seen in other CNS encephalitides.