A 68-year-old female patient came to our emergency department on December 28, 2022. The patient presented with fever, cough, and sputum 2 days ago, which could be reduced by taking antipyretic drugs. One day ago, the patient began to be confused and unresponsive, with mild immobility, slurred speech, and consciousness impairment.

The patient was poor in calculation and memory. The facial lines were approximately symmetrical, the tongue was extended centrally, the muscle strength of the limbs was grade 5, the muscle tone was normal, and bilateral Babinski syndrome was negative. The neck was soft and Kernig syndrome negative. There was no abnormality in cardiopulmonary auscultation. A nasopharyngeal swab for reverse transcription polymerase chain reaction (RT-PCR) of SARS-CoV-2 nucleic acid came back positive (Fig. 1A), confirming the diagnosis of SARS-CoV-2 infection. The RT-PCR test was used commercial detection kit produced by BioGerm (Shanghai, China). The amplified genomic regions of SARS-CoV-2 were ORF1ab gene (13,342–13,460) and N gene (28,881–28,979). Nucleic acid detection of SARS-CoV-2 was also performed using cerebrospinal fluid, which was weakly positive (Fig. 1B).

Real-time RT-PCR graph. A Positive nasopharyngeal swabs for SARS-CoV-2 RNA by real-time RT-PCR on ABI QuantStudio5 using the BioGerm SARS-CoV-2 nucleic acid detection kit. B Positive SARS-CoV-2 RNA in CSF by real-time RT-PCR on ABI QuantStudio5 using the BioGerm SARS-CoV-2 kit

Magnetic resonance imaging (MRI) of t he brain showed multiple abnormal signals in brain, predominantly bilateral symmetrical lesions in the thalamus (Fig. 2). Considering the possibility of inflammation, viral encephalitis, or autoimmune inflammation was suspected. Magnetic resonance venography (MRV) excluded venous cerebral infarction and magnetic resonance angiography (MRA) did not show any significant abnormality. For further diagnosis and treatment, the patient was admitted with “viral encephalitis.”

Symmetrical A T1WI low signal, B T2WI high signal, C FLAIR slightly high signal, D DWI showing equal signal in bilateral thalamus

After admission, the patient was given acyclovir for antiviral therapy, methylprednisolone for anti-inflammatory, and mannitol for cranial pressure reduction. Meanwhile, a lumbar puncture was performed. Her cerebrospinal fluid was clear and colorless with an initial pressure of 140 mmH2O. India ink staining for cryptococci: no abnormalities were seen. Cerebrospinal fluid (CSF) routine cell count examination: no abnormalities were found. The levels of four cerebrospinal fluid proteins were microalbumin 1089.2 mg/L, immunoglobulin G 175.4 mg/L, α2-macroglobulin 14.9 mg/L, and β2-microglobulin 6.35 mg/L. The six autoimmune encephalitis-related antibodies, anti-glutamate receptor (NMDA type) antibody IgG, anti-glutamate receptor (AMPA type 1) antibody IgG, anti-glutamate receptor (AMPA type 2) antibody IgG, anti-leucine-rich glioma inactivating protein 1, anti-γ-aminobutyric acid type B receptor antibody IgG, and anti-contact protein-associated protein 2 antibody IgG were all negative. Anti-Aqueous Channel Protein 4 antibody, anti-myelin basic protein antibody and anti-myelin oligodendrocyte glycoprotein antibody were all negative. IgG antibodies against SARS-CoV-2 were measured both in serum and CSF using a magnetic particle chemiluminescence kit produced by Autobio (Zhengzhou, China). The concentrations of IgG against SARS-CoV-2 in serum and CSF were 87.2 S/CO and 30.5 S/CO, respectively. According to the manufacturer’s instruction, S/CO ≥ 1.0 was positive. Since the etiological diagnosis was clear, the patient was diagnosed as COVID-19 encephalitis. After diagnosis, the therapy was adjusted and Azvudine (Genuine Biotech, China) antiviral therapy was given.

On the second day after admission, the patient’s confusion was better than before, and her calculation ability, memory, and orientation were all better than admission. There was no immobility of limbs, slurred speech, and impaired consciousness.

On the seventh day, the patient’s condition was stable, with significant improvement in confusion compared with admission. There were no obvious abnormal signs of cerebral MRV. MRI showed that encephalitis got better significantly after treatment (Fig. 3). Considering her condition was stable, she could be discharged from hospital. She was advised to continue oral hormone therapy and reduce dosage every day. Besides, she should avoid catching cold and go to the neurology department for follow-up examination 2 weeks later. The patient returned to the hospital on schedule and was in good condition.

Abnormal signals of bilateral thalamic lesions disappear after 10 days of treatment