Antibody-mediated LGI1 Encephalitis: Symptoms, Biomarkers, and Mechanisms of the Chronic Phase of the Disease

The encephalitis mediated by antibodies against Leucine-rich, glioma inactivated 1 protein (anti-LGI1 encephalitis) predominantly affects men (M:F, 6:4) and mostly older than 60 years. The disease has two distinct clinical phases: The acute phase in which the majority of patients develop severe short-term memory deficits (unable to remember events or experiences that occurred a few minutes earlier). This memory impairment can be preceded or accompanied by one or more of the following: hyponatremia (60% of patients), a highly distinctive type of seizures called facio-brachial dystonic seizures (\~40% of patients), along with confusion, irritability and other types of focal seizures or less frequently, generalized seizures. In addition, many patients at this stage have symptoms of REM sleep behavior disorder. In this stage, the CSF may show pleocytosis or mild increase of proteins, the EEG is usually abnormal, and in \~60% of the patients the MRI shows typical increased FLAIR signal in medial temporal lobes (11). There is a clinical sub-phenotype (\~13% of patients) in which the disease presents as a rapidly progressive cognitive decline without the indicated FLAIR MRI changes. About 70% of patients improve rapidly with corticosteroids and immunotherapy (eg, intravenous immunoglobulins and/or plasma exchange), but the improvement is often partial. After the acute phase, there is a chronic or residual phase which represents the interval from improvement of initial symptoms until the disease is considered no longer active and the remaining symptoms are thought to be irreversible. This chronic phase may take several months (it has been less well studied), and is characterized by the absence of CSF pleocytosis and inflammatory MRI changes (albeit this may show residual hippocampal atrophy), and very low or undetectable titers of serum antibodies. Most patients are unable to return to their job or previous activities due to residual (irreversible) memory or cognitive defic