Cerebrospinal fluid from COVID-19 patients with olfactory/gustatory dysfunction: A review

OBJECTIVE: We reviewed the literature on cerebrospinal fluid (CSF) testing in patients with altered olfactory/gustatory function due to COVID-19 for evidence of viral neuroinvasion. METHODS: We performed a systematic review of Medline and Embase to identify publications that described at least one patient with COVID-19 who had altered olfactory/gustatory function and had CSF testing performed. The search ranged from December 1, 2019 to November 18, 2020. RESULTS: We identified 51 publications that described 70 patients who met inclusion criteria. Of 51 patients who had CSF SARS-CoV-2 PCR testing, 3 (6%) patients had positive results and 1 (2%) patient had indeterminate results. Cycle threshold (Ct; the number of amplification cycles required for the target gene to exceed the threshold, which is inversely related to viral load) was not provided for the patients with a positive PCR. The patient with indeterminate results had a Ct of 37 initially, then no evidence of SARS-CoV-2 RNA on repeat testing. Of 6 patients who had CSF SARS-CoV-2 antibody testing, 3 (50%) were positive. Testing to distinguish intrathecal antibody synthesis from transudation of antibodies to the CSF via breakdown of the blood-brain barrier was performed in 1/3 (33%) patients; this demonstrated antibody transmission to the CSF via transudation. CONCLUSION: Detection of SARS-CoV-2 in CSF via PCR or evaluation for intrathecal antibody synthesis appears to be rare in patients with altered olfactory/gustatory function. While pathology studies are needed, our review suggests it is unlikely that these symptoms are related to viral neuroinvasion.