AMPAR (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GluR2) antibody encephalitis in a Myasthenia Gravis (MG) patient who received thymectomy for thymoma is extremely rare. There is only one published case report of such a patient. This abstract demonstrates another similar case.

A 43-year-old female with history of MG status post thymectomy for malignant thymoma presented with encephalopathy and altered mental status. Her initial exam showed impaired concentration and lethargy. She was empirically treated with antimicrobials for suspected meningitis/encephalitis. She later developed right facial paresis. She then had an episode of right gaze deviation with worsening of consciousness, so she required mechanical ventilatory support for airway protection and was treated with levetiracetam for seizures.

MRI brain revealed multifocal T2/FLAIR hyperintensities most prominent in the frontal lobes without diffusion restriction. CSF analysis showed protein 85, white count 60 with lymphocytic predominance and normal glucose. Serum Herpes Simplex Virus (HSV) 1 antibody was positive so patient remained on Acyclovir but later CSF nucleic acid amino transferase HSV PCR was negative. Routine thyroid function studies were normal but serum Anti-thyroid peroxidase antibody and AMPAR IgG titers were elevated. Continuous electroencephalogram showed diffuse cerebral slowing and frontal intermittent rhythmic delta activity without electrographical seizures. She received a 5-day course of IVIG with minimal clinical improvement. After infectious etiologies were excluded, she received a 5-day course of methylprednisolone. Due to therapeutic failure, she was treated with plasma exchange. CT chest revealed no recurrence of tumor. MRI abdomen and pelvis revealed uterine fibroids. With little clinical improvement, she received tracheostomy and PEG tube placement and was discharged to long term care facility.

This patient had a poor clinical outcome. Therefore, it is important to further understand the pathology and have low threshold for treating AMPAR antibody encephalitis in a patient with history of MG and thymoma status post thymectomy.