Cytotoxic Lesions of the Corpus Callosum (CLOCC) Suggesting Exacerbation by Heterogeneous COVID-19 Booster Vaccination.

Cytotoxic lesions of the corpus callosum (CLOCC) is a disease entity associated with reversible lesions of the corpus callosum on magnetic resonance imaging (MRI). CLOCC is caused by a variety of etiologies, but CLOCC after vaccination is extremely rare. Four prior cases of CLOCC after the first dose of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccine have been reported; these were localized to the splenium and showed early clinical and neuroradiological recovery. We experienced an unusual case in which a heterogeneous COVID-19 booster vaccination caused rather severe CLOCC damage. A 74-year-old Japanese woman presented with ataxia, high fever, and hearing loss several days after her third vaccination against COVID-19. This booster was an mRNA-1273 while her first and second vaccinations were both BNT162b2 type. SARS-CoV-2 real-time reverse transcriptase polymerase chain reaction (RT-PCR) analysis was negative, but serum SARS-CoV-2 S-IgG antibodies were elevated. Her cerebrospinal fluid (CSF) showed an elevated cell count and high levels of protein and interleukin-6 (IL-6). Brain MRI showed CLOCC spreading throughout the body of the corpus callosum. After the exclusion of other potential causes, the diagnosis of vaccination-related CLOCC was made. Six months later, recovery of clinical and MRI findings remained incomplete. It was suggested that the patient's CLOCC might have been caused by the increase in CSF IL-6 due to an enhanced immune response from the heterogeneous vaccination, resulting in more severe damage to the corpus callosum than usual.