When a patient presents with rapidly progressive short-term memory deficits accompanied by involuntary muscle movements (myoclonus) or sleep-related jerks, clinicians must look beyond typical neurodegenerative dementias. Autoimmune limbic encephalitis - specifically mediated by leucine-rich glioma-inactivated 1 (LGI1) antibodies - is a crucial treatable diagnosis to consider.
LGI1-antibody encephalitis predominantly affects males (2:1 ratio) and typically manifests with subacute memory failure, sleep disruption, hyponatremia (present in ~60% of cases), and characteristic faciobrachial dystonic or tonic seizures. Neuroimaging often demonstrates bilateral medial temporal lobe, hippocampal, and amygdalar hyperintensities on T2/FLAIR MRI sequences. Distinguishing this entity from viral encephalitis, Creutzfeldt-Jakob disease, or paraneoplastic syndromes via antibody panel testing (VGKC/LGI1) is critical. Early initiation of high-dose corticosteroid therapy or immunotherapy frequently yields significant clinical recovery and restores cognitive function.