Brain astrocytoma misdiagnosed as anti-NMDAR encephalitis: a case report

BACKGROUND: Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis, which is the most common type of autoimmune encephalitis, is caused by the production of autoantibodies against NMDA receptor. Anti-NMDAR encephalitis patients present with various non-specific symptoms, such as abnormal psychiatric or behaviour, speech dysfunction, cognitive dysfunction, seizures, movement disorders, decreased level of consciousness, and central hypoventilation or autonomic dysfunction. CASE PRESENTATION: A 67-year-old man presented with new-onset focal seizures. The brain magnetic resonance imaging (MRI) plain scan and enhanced scan showed abnormal signal on the proximal midline frontoparietal junction region. Anti-NMDAR antibody was detected in cerebrospinal fluid (CSF) and serum using a commercial kit (Euroimmune, Germany) by indirect immunofluorescence testing (IIFT) according to the manufacturer’s instructions for twice. Both of the test results were positive in CSF and serum. The patient was diagnosed as anti-NMDAR encephalitis and then was treated repeatedly with large dose of intravenous corticosteroids and gamma globulin. Accordingly, the refractory nature of seizures in this case may be attributed to NMDAR autoantibodies. When the patient presented at the hospital for the third time, the brain MRI revealed an increase in the size of the frontal parietal lesion and one new lesion in the left basal ganglia. The patient underwent a surgical biopsy and astrocytoma was confirmed by histopathology. CONCLUSIONS: Although the sensitivity and specificity of anti-NMDAR-IgG antibodies in CSF to diagnose anti-NMDAR encephalitis are close to 100%, it is not absolute. Anti-NMDAR antibodies were positive, which might make the diagnosis more complex. The diagnosis of atypical presentation of anti-NMDAR encephalitis requires reasonable exclusion of other disorders.