Endocrine Abstracts

JOINT3098

Antibodies against LGI-1 (Leucine-rich glioma-inactivated 1) were first described in 2010¹. LGI-1 antibody encephalitis is rare with an incidence of 0.83 per million persons per year². It is more common in men and has a median age of onset of 65 years. It is characterised by features of limbic encephalitis with frequent focal seizures and associated hyponatraemia is common. We present the case of a 73yo man who presented to the emergency department with a transient episode of expressive aphasia and numbness of his right hand that lasted approximately 15 minutes. Background medical history included diverticular disease, hiatus hernia, hypercholesterolaemia and benign prostatic hypertrophy. He was not taking any regular medications at the time of admission. He had a good functional baseline and was independent in all activities of daily living. Examination was unremarkable and he was noted to be clinically euvolaemic. CT brain and subsequent MRI brain did not show any acute abnormalities. Serum sodium on admission was 126mmol/lwith serum osmolality 257mmol/kg and urine sodium 71mmol/lwith urine osmolality 552mmol/kg, in keeping with syndrome of inappropriate antidiuresis (SIAD). Thyroid function tests were normal and random cortisol was 263nmol/lso he underwent a short synacthen test which had a 30 minute cortisol value of 752nmol/L. CT thorax, abdomen and pelvis did not show any evidence of malignancy. Sodium improved following fluid restriction and he was discharged home. He represented 2 weeks later with a generalised tonic clonic seizure. On further questioning his wife recounted fluctuating memory over the last few months, sleep disturbance and a change in mood. He was commenced on levetiracetam and had investigations for autoimmune encephalitis. A serum sample detected the presence of LGI-1 antibodies. He completed a course of intravenous immunoglobulin followed by plasma exchange. Sodium increased to 135mmol/land he has not had any further seizure events. The diagnosis of LGI-1 antibody encephalitis provided a unifying diagnosis in this case. In cases of SIAD it is important to consider alternative aetiologies where a cause is not immediately obvious and LGI-1 antibody encephalitis is an important diagnosis to consider in older adults presenting with SIAD, neurological and cognitive symptoms.

References: 1. Irani SR. Autoimmune Encephalitis. Continuum (Minneap Minn). 2024;30(4):995-1020. 2. van Sonderen A, Thijs RD, Coenders EC, Jiskoot LC, Sanchez E, de Bruijn MA, et al. Anti-LGI1 encephalitis: Clinical syndrome and long-term follow-up. Neurology. 2016;87(14):1449-56.