Virginia Research Day 2025

Medical Resident Research Case Reports

18 Short Term Memory Loss in the Setting of Limbic Encephalitis

Patrick Pagaduan, DO; Faryal Mirza, MD Corresponding author: patrick.pagaduan@lpnt.net

SOVAH Health Internal Medicine Residency Program

Encephalitis is an inflammation of the brain parenchyma, which affects 3.5 to 7.5 per 100,000 people, with the highest incidence in the young and elderly. Encephalitis is commonly caused by viral, bacterial, parasitic, or fungal infection, an antibody mediated autoimmune response, or a paraneoplastic manifestation. Encephalitis is defined by the presence of altered consciousness for more than 24 hours and at least three minor criteria: fever, new-onset seizure, new-onset focal neurologic findings, CSF pleocytosis, and abnormal MRI or electroencephalographic findings. The causative agent is unknown in 37% to 70% of infections. Limbic encephalitis is inflammation of brain tissue that primarily affects the limbic system in the medial temporal lobes. The primary limbic system function is to process and regulate emotion and memory while also dealing with sexual stimulation and learning. Behavior, motivation, long-term memory, and our sense of smell also relate to the limbic system.

Here we present a 66-year-old Caucasian male with a history significant for essential tremor on lamotrigine and primidone who presented with confusion. While in the emergency department, he developed a tonic clonic seizure, lasting approximately 1 minute which resolved after 2 mg Ativan was given. Initial workup was done with a head CT which was negative for acute intracranial findings. An electroencephalogram was performed and was within normal limits. A lumbar puncture was performed and showed WBC: 6 cell/microliter, 41% segmented neutrophils, 40% lymphocytes, 19% monocytes, glucose: 68 mg/ deciliter, total protein 96 mg/deciliter. Cerebrospinal fluid Gram stain was negative, CSF culture showed no growth, and Herpes Simplex Virus CSF was negative. A Brain MRI was performed which showed abnormal symmetrically increased T2 hyperintense signal within the medial temporal lobes bilaterally suspicious for limbic encephalitis. IV Acyclovir was initiated to cover for viral encephalitis and IV steroids

to cover for auto-immune encephalitis. Testing for auto-immune markers including Anti-GAD, Anti-CASPR2, and Anti-LGI1 and tumor markers including CEA, CA 15-3, CA 125, and PSA were negative. Patient’s confusion improved, and he was discharged to skilled nursing facility to undergo rehab. This case highlights a typical presentation of limbic encephalitis. The most common cause is a viral infection from Herpes simplex, and treatment should include Acyclovir. PCR sensitivity and specificity for Herpes Simplex Encephalitis were reported as 98 and 94%, with positive and negative predictive values of 95 and 98%. However, in patients with high clinical probability of Herpes simplex encephalitis, a negative PCR result, while decreasing the likelihood, does not entirely exclude the possibility of infection, and patient should still be treated empirically.

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