IgG-NR2B-A Potentially Valuable Biomarker in the Management of Refractory Anti-NMDAR Encephalitis

The autoantibodies against the NR1 subunit are well known in the pathomechanism of NMDAR encephalitis. The dysfunction of the NR2 subunit could be a critical factor in this neurological disorder due to its important role in the postsynaptic pathways that direct synaptic plasticity. We report a case of paraneoplastic anti-NMDAR encephalitis presented alongside very severe illness. Computed tomography (CT) of the brain, as well as FLAIR and T2-weighted MRI, was performed to rule out any other acute brain processes. A semi-quantitative method was applied to detect the presence of anti-NMDAR antibodies in the serum and CSF. A CT chest-abdomen-pelvis scan was performed that detected an ovarian teratoma. A histopathological examination was performed after a laparoscopic right-ovary cystectomy. Subsequent immunofluorescence immunohistochemical staining showed the expression of NMDA receptors of type NR2B. Treatment included first-line immunotherapy, second-line immunotherapy, tumor removal, and intrathecal injections with methotrexate and dexamethasone. The histological finding for our patient after tumor removal was ovarian teratoma. Hematoxylin-eosin (HE) staining revealed a characteristic spectrum of elements, including stratified squamous epithelium and fat tissue accompanied by neuroglial cells. Subsequent immunohistochemical staining showed an expression of NMDA receptors of type NR2B in different structures of the teratoma, including the neuroglial cells. The first-line immunotherapy following the tumor removal was insufficient in our patient. The paraneoplastic anti-NMDAR encephalitis with a coexpressed NR2B subunit on the neural cells of the ovarian teratoma may suggest a different inflammation process and could be the key factor in the pathomechanism and treatment of the refractory anti-NMDAR encephalitis.