2371 Not all NMDA antibodies are equal: two cases of Glioblastoma multiforme presenting with subacute neurological syndromes and positive NMDA antibodies

• Published in: BMJ neurology open Vol. 4; no. Suppl 1; p. A48
• Main Authors: Chatterton, Sophie, Clarke, Antonia, Satgunaseelan, Laveniya, Soh, Hwei Choo, Ng, Karl, Parratt, Kaitlyn, Parratt, John
• Format: Journal Article
• Language: English
• Published: London BMJ Publishing Group Ltd 01.08.2022; BMJ Publishing Group LTD
• Subjects: Abstracts; Antibodies; Biopsy; Brain cancer; Encephalitis; Immunotherapy
• ISSN: 2632-6140
• DOI: 10.1136/bmjno-2022-ANZAN.127

While the specificity of anti-NMDAR-IgG in serum and particularly in CSF is high, false positive results do occur and may lead to an erroneous diagnosis of autoimmune encephalitis. We describe two cases of glioblastoma multiforme (GBM) presenting with neurological syndromes and positive anti-NMDA antibodies. Initial immunotherapy was given based on autoimmune findings, while clinical/radiological red flags in both cases lead to the final diagnosis of GBM. Case 1: A 64-year-old male presented following seizures on a background of subtle mood changes. MRI brain demonstrated increased T2/FLAIR signal of the left temporal lobe, and he returned positive serum and CSF anti-NMDAR antibodies. Intravenous immunoglobulin (IVIg) was administered with initial improvement however due to atypical imaging findings he underwent a brain biopsy confirming grade 4 GBM. Case 2: A 38-year-old male presented with refractory status-epilepticus following subacute symptoms of neuropsychiatric changes. MRI brain again showed increased T2/FLAIR signal affecting the left temporal lobe. He returned positive serum NMDAR antibodies that were negative in CSF (delayed lumbar puncture due to initial concerns of raised intracranial pressure). He received plasmapheresis, methylprednisolone, IVIg and rituximab, with prompt clinical and initial radiographic improvement. Interval MRIs however demonstrated atypical progressive imaging changes and a brain biopsy was performed, also confirming a grade 4 GBM.ConclusionsClinicians should have a heightened awareness of the possibility of intrinsic cerebral tumours presenting as a mimic of NMDAR-mediated encephalitis. Clinical and/or radiological progression despite immunotherapy and atypical features at presentation can alert clinicians to this entity.