Anti-N-methyl-D-aspartate Encephalitis Concomitantly with Tall-cell Variant Papillary Thyroid Carcinoma.

Anti-N-methyl-D-aspartate (NMDA) encephalitis is an autoimmune-mediated process characterized by psychosis, seizures, dyskinetic movements, and autonomic instability. At least half of the reported cases are paraneoplastic, particularly associated with an ovarian teratoma. None have been reported to be associated with thyroid tumor. We present a case of anti-NMDA encephalitis concomitantly occurring in setting of papillary thyroid carcinoma in a woman who presented with headaches, myalgia and somnolence mimicking meningoencephalitis. A 29-year-old African female presented with fever, headache, myalgia, somnolence and behavioral changes. Initial evaluation was significant for lymphocytic pleocytosis with normal glucose and protein. She was started on broad spectrum empiric antibiotics. Despite antibiotics, she continued to have worsening encephalopathy, hallucinations, epileptic seizures, and multifocal dyskinesias involving the face and extremities with no electroencephalogram correlate. Extensive infectious workup was unremarkable. Whole-body CT with contrast and ovarian ultrasound were unremarkable for malignancy. Serum auto-antibodies to the NMDA receptor and thyroid peroxidase were detected. She was treated with high-dose intravenous steroids, plasmapheresis, intravenous immunoglobulin, and rituximab with no clinical or serological response. Fluorodeoxyglucose positron emission tomography (FDG-PET) showed a hypermetabolic thyroid nodule. Fine needle aspiration of the nodule revealed papillary thyroid carcinoma. She underwent total thyroidectomy and pathology showed two foci of tall-cell variant papillary thyroid carcinoma. Serological and clinical response followed shortly after tumor resection. The NMDA receptor stain of the papillary thyroid carcinoma was nonreactive. We describe the coincidentally co-occurrence of NMDA encephalitis in a patient with papillary thyroid carcinoma. This case highlights the importance of presumed cases of non-paraneoplastic NMDA encephalitis, FDG-PET may help in detecting occult malignancies.