A Case of Heavy Chain Neuronal Intermediate Filament Autoimmune Encephalitis

A 66-year-old woman presented with 2 days of confusion, poor balance, and a recent ground level fall. She exhibited lower extremity weakness, urinary retention, and upper extremity resting tremor with cogwheel rigidity. Extensive work-up for electrolyte, infectious, and rheumatologic pathologies was unremarkable, and she was ultimately found to have heavy chain neuronal intermediate filament (NIF-H) antibodies in the cerebrospinal fluid, supporting a diagnosis of NIF autoimmune encephalitis (AE). An increased awareness of AE and a high index of suspicion are key to prompt diagnosis and treatment. If diagnosed, cancer screening is recommended, because AE can be a paraneoplastic process.