Leucine-rich glioma-inactivated protein 1 antibody-positive limbic encephalitis in a patient with an early-stage asymptomatic breast cancer

Our patient is a woman who developed a subacute amnestic syndrome, followed by cognitive impairment, headache, temporal lobe epilepsy and hyponatraemia. An early-stage asymptomatic breast cancer was identified on positron emission tomography (PET) scan. After treatment with immunotherapy with high-dose corticosteroids, intravenous immunoglobulins, upfront rituximab and excision of the tumour, the patient gradually recovered. Partial retrograde and anterograde amnesia persisted during the initial weeks, followed by slow and steady improvement. Autoimmune encephalitis is a severe neurological disorder associated with antibodies against neuronal cell-surface or intracellular onconeural proteins. Anti-leucine-rich glioma inactivated 1 (LGI1) predominantly affects males in the seventh decade of life, and less than 10% of all cases are associated with cancer. Paraneoplastic cases have been associated with malignant thymoma, neuroendocrine tumours and mesothelioma and usually had Morvan syndrome, in which serum antibodies are more frequently directed against CASPR2 than against LGI1. We report the first well-documented case of anti-LGI1 limbic encephalitis in a woman with newly diagnosed breast cancer.