Autoimmune encephalitis is a heterogeneous collection of disorders that remains a clinical challenge for the practicing neurologist. Leucine-Rich Glioma Inactivated Protein-1 (LGI1) is an antibody known to cause autoimmune encephalitis associated with faciobrachial dystonic seizures most seen in men in the sixth decade of life. As this antibody is more frequently identified, the heterogeneity of this condition is becoming clear. In our case, we describe an atypical presentation of IGL-1 autoimmune encephalitis with brisk improvement on immunotherapy.

A 77-year-old female with a history of anxiety, hyponatremia for two years, and previous lacunar stroke who presented to a large military medical center for multiple witnessed generalized tonic seizures. On further history, the family noted four months to several years of profound decline to include memory and ability to complete her ADLs. Neurologic exam was unremarkable except for a MOCA of 16/30 related mostly to recall.  EEG showed recurrent frontotemporal seizures that spread bilaterally with arrest of speech and hyperventilation and MRI showed bilateral FLAIR mesial temporal hyperintensities. LP had normal protein and cells. Malignancy screening was negative. Patient was treated for autoimmune encephalitis with 5 days of 1 gram methylprednisolone and IV immunoglobulin with clinical improvement after CSF and serum lab studies returned with evidence of LGI1 autoantibodies. Upon discharge, the patient was started on rituximab and after 4 months, the patient demonstrated near complete return of her long-term memory.

This case demonstrates the clinical heterogeneity of IGL-1 autoimmune encephalitis and the importance of considering this condition in patients with subacute cognitive decline and seizures. Patient demographics, chronic hyponatremia prior to cognitive decline, and the absence of faciobrachial dystonic seizures make this case particularly unique. It is critical for neurologists to be able to accurately diagnose this condition given the possibility for improvement with appropriate treatment.