6th August 2024

Autoimmune and paraneoplastic encephalitis

These are rarer but clinically extremely significant causes of encephalitis. Paraneoplastic encephalitis refers to an autoimmune process that is associated specifically with a malignancy, whilst autoimmune encephalitis may happen in the absence of a malignant process. Several important causes are summarised below.

Anti-NMDA receptor encephalitis

This is a rapidly progressing encephalitis that affects predominantly young women and presents with a prominent psychiatric component, motor features, seizures, autonomic dysfunction, and occasionally severe hypoventilation. It can be preceded by a mild viral-type illness. It has a strong association with ovarian teratomas and should prompt a search for such a tumour. It may also be associated with small-cell lung cancer and testicular teratoma. Formal diagnosis is by anti-NMDA receptor antibodies in blood and CSF (with the latter being more specific), though these may take time, so diagnosis is frequently made on clinical grounds. Treatment is with immunomodulation (e.g. methylprednisolone ± IVIg or rituximab), as well as management of any neoplasm found.

Paraneoplastic encephalitis

Some malignancies are associated with autoimmune processes that target the central and/or peripheral nervous system. Classically, this is a limbic encephalitis, presenting with prominent behavioural or mood components but also with seizures and cognitive dysfunction. There may also be involvement of the brainstem or descending CNS tracts. One of the most frequent associations is with small-cell lung cancer by way of anti-Hu antibodies, though there is a wide range of autoantibodies and cancer types associated with CNS involvement. Treatment, again, utilises immunomodulatory agents in combination with management of the underlying malignancy.