Anti-N-Methyl-D-Aspartate Receptor Encephalitis in a Patient With Antithyroid Peroxidase Antibodies and a Parotid Pleomorphic Adenoma.

Background: Anti-N-methyl-D-aspartate receptor (NMDA-R) encephalitis is an autoimmune disorder first described in 2007. It can cause severe neurologic and psychiatric symptoms, and patients often are misdiagnosed with a primary psychiatric disorder. Anti-NMDA-R encephalitis is an important differential diagnosis of psychosis, as the condition can be treated with the appropriate therapy. Case Report: A 42-year-old female with a history of hypothyroidism presented for evaluation of agitation and weakness. Six months prior to her presentation at our hospital, she had complained of headache, and neuroimaging showed a small right frontal hyperintensity on fluid-attenuated inversion recovery imaging. Workup was largely unremarkable, and she improved briefly with steroids at the outside institution. She then developed psychiatric symptoms and had 4 admissions to separate inpatient psychiatric facilities. She was tried on various antipsychotic medications and mood stabilizers with no improvement and lost 30 pounds in 3 months. When the patient was transferred to our facility, her neuroimaging was stable, and serum and cerebrospinal fluid were positive for antithyroid peroxidase and NMDA-R antibodies. She was treated with intravenous immunoglobulin (IVIG), high-dose steroids, and rituximab. Positron emission tomography scan revealed a parotid mass that was resected and determined to be a pleomorphic adenoma. The patient improved remarkably to her baseline and was able to return to full duties at work within 6 months. In the 2 years since her initial admission, she has had minor relapses that have responded well to rituximab and IVIG. Conclusion: This case demonstrates a typical presentation of anti-NMDA-R encephalitis, as well as the challenges that can delay diagnosis. Symptoms vary and are often psychiatric, making these patients difficult to diagnose clinically, and they therefore require thorough investigation. This case illustrates the necessity to be inquisitive and to challenge the diagnosis when a clinical picture is not congruent because an accurate diagnosis is imperative in guiding appropriate treatment.