Autoimmune encephalopathies are a heterogeneous group of rare diseases that are characterized by the appearance of various acute or subacute neurological disorders in secondary to an autoimmune attack (of the patient’s own defenses) to different parts of the brain, brainstem and cerebellum.

There are multiple diseases within this diagnostic category that share, to a greater or lesser extent, the appearance of alterations in the level of consciousness, alterations of higher functions (memory, speech, orientation, behavior …), movement disorders (abnormal postures, incoordination, tremor …), epileptic seizures (seizures, loss of consciousness …) and dysautonomia (alterations in respiratory or heart rate, alterations in blood pressure …).

They are, in general, serious illnesses, which require, very often, admission to Intensive Care Units. They can affect all types of patients, from children to the elderly, although each group of diseases is associated with patient profiles, symptoms, aggressiveness and response to specific treatments.

It is a group of diseases known since relatively recently. Previously they were very frequently attributed to viral infections but the discovery of different causative autoantibodies led to the possibility that many of the encephalopathies and encephalitis in which no germs were found could actually be produced by autoimmune mechanisms. Some of these diseases are associated with cancer, appearing as paraneoplastic diseases or as complications secondary to previous viral infections (herpes viruses), although they can also appear without any known trigger.

Autoimmune encephalopathies are classified according to the presence of the antibodies that cause them. There are multiple variants but the best known are:

• Encephalopathy with anti-NMDAR antibodies, is the most frequent and known. It appears predominantly in young women and is associated with relative frequency to ovarian teratomas. In children it can appear after a herpes virus infection.
• Encephalopathy with anti-LGI1 antibodies, appears in older people and is characterized by dystonic facio-brachial seizures.
• Encephalopathy with anti-CASPR2 antibodies or Morvan-Neuromyotonia Syndrome, presents as continuous muscle activity, itching, insomnia and psychosis. It is often associated with thymomas.
• Anti-Hu encephalitis, very often associated with tumors, especially lung. It can manifest itself with involvement of sensory neurons, limbic encephalitis or encephalitis of the brainstem.

The treatment of all these diseases is immunotherapy, including corticosteroids, intravenous immunoglobulins, plasma exchange (plasmapheresis), rituximab or cyclophosphamide among others.