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Abstract: SA-PO390

Severe Hyponatremia Associated with Autoimmune LGI1 Encephalitis, an Underrecognized Cause of SIADH

Session Information

Category: Trainee Case Report

  • 902 Fluid and Electrolytes: Clinical

Authors

  • Tio, Maria Clarissa, Brigham and Women's Hospital, Massachusetts General Hospital, Boston, Massachusetts, United States
  • Cheung, Pui Susan Wen, Massachusetts General Hospital, Boston, Massachusetts, United States
Introduction

SIADH is commonly caused by medications, malignancies, pain, and nausea, however autoummune encephalitis as a cause is often underrecognized. Here we present a case of severe SIADH secondary to autoimmune LGI-1 encephalitis.

Case Description

A 79-year-old male with hypertension on hydrochlorothiazide (HCTZ) presented to the ED 2 months prior for fatigue, and was found to have hyponatremia with serum Na (sNa) of 123mmol/L. It was attributed to HCTZ, and sNa improved to 127mmol/L after its discontinuation. A month later, patient was hospitalized for left arm twitching and recurrent hyponatremia with sNa 123mmol/L, sOsm 256mOsm/kg, uOsm 720mOsm/kg, serum Cr 0.81mg/dL. His twitches was associated with voluntary movements, occurred 3 times a day and each lasted for 10 seconds. Workups for SIADH were unrevealing. Given the concern for symptomatic hyponatremia with arm twitching, the patient was treated with ddavp and 3% saline for controlled sNa correction, and discharged with sNa 137mmol/L, on salt tablets, fluid restriction, and furosemide. Neurologic symptoms had improved.

Patient returned to clinic 3 weeks after discharge, and reported recurrence of left arm and hand twitching with increased frequency and severity, and now with new onset facial clenching. Labs showed normal sNa of 135mmol/L, sOsm 280mOsm/kg, uOsm 681mOsm/kg, Ca 9.6mg/dL. Patient was referred to Neurology Dystonia Clinic, and the diagnosis of anti-LGI1 encephalitis was confirmed with positive Leucine-rich, glioma inactivated 1 protein IgG (LGI1) and positive Voltage gated potassium channel Ab (VGKC). He was promptly treated with pulse methylprednisolone with resolution of his neurologic symptoms and hyponatremia.

Discussion

It is estimated that 60% of the patient with autoimmune LGI-1 encephalitis presented first to health care providers with hyponatremia, and yet, it is an under-recognized cause of SIADH. LGI-1 is part of the voltage-gated potassium channel complex present in the hippocampus and temporal cortex, and LGI-1 encephalitis is characterized by hyponatremia, acute or subacute cognitive impairment, faciobrachial dystonic seizures, psychiatric disturbances and epileptic seizure. If left untreated, patient would progress rapidly to end stage dementia resulting in death. However, if treated early with steroids, it has low relapse rate and good clinical outcome.