Reply to the Letter “COVID‐19‐Associated Encephalopathy and Cytokine‐Mediated Neuroinflammation”

Abstract

Muccioli et al proposed an interesting comparison between the case of encephalitis related to severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection we described and immune effector cell-associated neurotoxicity syndrome (ICANS). Indeed, the clinical phenotype characterized by akinetic mutism, normal brain magnetic resonance imaging (MRI), frontal slowness on electroencephalogram (EEG), hyperproteinorrachia with mild pleocytosis, and response to steroid treatment fit well with ICANS, and, more in general, with a central nervous system (CNS) cytokine-induced event. In this case, SARS-CoV-2 infection triggered neuroinflammation but the underlying mechanisms are unknown. In order to clarify the role of inflammation in pathogenesis, we measured the values of cytokines in serial serum samples obtained the same day of cerebrospinal fluid (CSF) analysis before and after steroid therapy. Interleukin (IL)-8 and IL-6 exhibited higher levels in CSF compared with serum with a reduction in both compartments after steroid therapy (Table1), in line with what is typically observed in ICANS.1 In addition to that, we here report the serial results of glial and astrocytic markers (triggering receptor expressed on myeloid cells 2 [TREM-2], chitinase-3-like protein 1 [YKL-40], and glial fibrillary acidic protein [GFAP]). The patient exhibited increased CSF levels of TREM-2, a microglia activation marker able to modulate neuroinflammation in acute and chronic CNS disorders. Furthermore, GFAP, a CNS-specific astrocyte marker recently pointed out as main driver of ICANS2 appeared to be elevated, despite neuronal damage markers at the upper limit of normal distribution. These results fit well with the recent observation of increased plasma levels of GFAP and NfL detected in patients with moderate to severe coronavirus disease 2019 (COVID-19).3 The patient also presented elevation of YKL-40, a glial glycoprotein known to be released in cytokine-stress syndromes by activation of TNF-alpha and IL-6. These additional findings further support cytokine-mediated neuroinflammation as the main driver of encephalitis in this patient. The high levels of interleukins in CSF compared with serum, as well as the increase of CNS-specific GFAP, speak against passive leakage across the blood–brain barrier, and instead suggest an intrathecally active inflammatory process. Several works reported similar cases during the last months,4-6 showing that many patients with SARS-CoV-2 encephalitis exhibited clinical and imaging findings highly consistent with previously reported inflammatory-mediated neurotoxicity,1, 2 whereas direct invasion and autoimmune responses appeared to be a rare condition. Despite the interesting insights given by this case report, larger studies are urgently needed to confirm cytokine-induced neuroinflammation as a main driver of SARS-CoV-2 related encephalitis, as this issue has deep consequences for the management and treatment of this growing condition worldwide. We thank the patient for his participation in the study. Andrea Pilotto and Alessandro Padovani: study concept and design, acquisition of data, analysis and interpretation of data, drafting/revising the manuscript for content. Nothing to disclose.

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