Case Challenge: Behavior Changes, Seizures, and Hyponatremia

Case

Clinical Presentation

Mr. L. is a white man, age 67, who presented after several weeks of personality changes, paranoid behavior, emotional lability, and encephalopathy. At admission, he experienced a generalized tonic-clonic seizure and was found to have hyponatremia (Na⁺ = 119 mEq/L), which was treated. When his sodium levels had normalized, he was discharged. Later he returned, having another generalized tonic-clonic seizure and was again noted to have hyponatremia. Despite sodium correction, his mental status continued to deteriorate. He appeared confused with difficulty remembering, paranoia, and emotional lability.

Diagnostic Testing & Diagnosis

Mr. L had a brain MRI with and without contrast, lumbar puncture and cerebrospinal fluid (CSF) analysis, video-EEG, a full-body fluorodeoxyglucose positron emission tomography (FDG-PET) scan, and serum antibody testing (Table). He also had video-EEG that showed mild generalized slowing but no ictal foci. During monitoring, he had subtle twitches of the left side of the face, shoulder, and arm intermittently.

Serum and CSF were sent for an autoimmune encephalitis panel test, and results were positive for antibodies to leucine-rich glioma-inactivated protein 1 (LGI1), confirming the diagnosis of anti-LGI1 autoimmune encephalitis.

Treatment and Follow-Up

Mr. L. was treated with intravenous high-dose steroids, and his encephalopathy and hyponatremia gradually resolved, with some persistent difficulties with memory. He subsequently received 1 gram rituximab to achieve B-cell depletion in an attempt to decrease the risk of relapses. At 6-month follow-up, he was relapse free and improving.

Challenge Questions

1. LGI1 antibody-mediated autoimmune encephalitis typically affects:
A. Women more than men
B. Older adults
C. Younger adults
D. People of all ages

2. Anti-LGI1 antibody encephalitis typically takes the following clinical course:

A. A monophasic illness
B. A progressive illness despite immunotherapy
C. Relapsing in about
D. Relapsing in nearly 35% of patients 100% of patients

3. Anti-LGI1 antibody encephalitis is:
A. Most often associated
B. Occasionally associated with small cell lung cancer with thymomas
C. Never paraneoplastic
D. Always paraneoplastic

4. Faciobrachial dystonic seizures (FBDS) with anti- LGI1 antibody-mediated encephalitis respond best to:
A. Levetiracetam
B. Phenytoin
C. Intravenous corticosteroids
D. Valproic acid

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