In this article the authors reviewed the literature on cerebrospinal fluid (CSF) testing in patients with altered olfactory/gustatory function due to COVID-19 for evidence of viral neuroinvasion. They 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. 51 publications were identified 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. The authors concluded that 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.
Lewis A, Frontera J, Placantonakis DG, Galetta S, Balcer L, Melmed KR. Cerebrospinal fluid from COVID-19 patients with olfactory/gustatory dysfunction: A review. Clin Neurol Neurosurg. 2021 Jun 12;207:106760. doi: 10.1016/j.clineuro.2021.106760