1.1 COVID-19 and the nervous system
COVID-19 can affect the nervous system and cause nervous system disorders. There are three major types of neurological manifestations in COVID-19 patients, involving the central nervous system, peripheral nervous system, and skeletal muscles. In comparison with mild COVID-19 cases, patients with these neurological symptoms are older and more frequently have underlying diseases, of which hypertension is the most common [2]. In a study of 417 COVID-19 patients with mild symptoms, 85.6% and 88.0% of patients had olfactory and taste dysfunction [3]. Previous reports have documented that neuroinvasiveness is a common feature of CoV. Although a specific mechanism by which SARS-CoV-2 infects neural cells was not yet known, viral RNA has been detected in the cerebrospinal fluid of COVID-19 patients. Considering the possibility of the invasion of the nervous system by SARS-CoV-2, the risk of its infection may be currently underestimated [4].