Immunotherapeutics for autoimmune encephalopathies and dementias.

The timely implementation of immunotherapy is key to successful treatment of autoimmune encephalopathies or dementias (from here on will be referred to as autoimmune encephalopathies). There are different levels of diagnostic certainty which should guide the immunological treatment of autoimmune encephalopathies. There is a high level of diagnostic certainty for patients who have classic limbic encephalitis and have a neural antibody detected in serum or CSF (such as potassium channel complex antibody). For these patients, initiating high-dose corticosteroids or IVIg is indicated, with plasma exchange, rituximab or cyclophosphamide used as second-line therapy if first-line therapy proves only partially beneficial. There is a lower level of diagnostic certainty in patients with non-limbic atypical phenotypes (though rapidly progressive) when no neural antibody is detected in serum and CSF. A trial of corticosteroids or IVIg (or both sequentially) may be undertaken in these patients, but if no objective improvements occur, further immunotherapy is unlikely to be beneficial. Antiepileptic treatment also plays a critical role in those who have seizures as well as cognitive symptoms. Evaluation for and treatment of any underlying cancer is another component for those patients with a paraneoplastic cause of encephalitis. An individualized maintenance regimen needs to be designed for patients who do improve with immunotherapy. Individual factors that need to be considered when formulating a program of maintenance treatment include disease severity, antibody specificity and proclivity for disease relapse. Azathioprine and mycophenolate mofetil are frequently used for the purpose of remission maintenance, and should permit gradual withdrawal of steroids, IVIg or more toxic immunosuppressants. The duration of maintenance therapy is uncertain, but this author typically recommends 3-5 years of relapse-free maintenance treatment before discontinuing immunotherapy altogether.