Seizures are common in all types of autoimmune encephalitis, but their frequency and severity are particularly relevant in anti-NMDAR, anti-GABAbR, anti-GABAaR, and anti-LGI encephalitis. Seizures occur in>70% of patients in the acute phase of anti-NMDAR encephalitis without specific or distinctive features that may suggest this disorder. In anti-GABAbR and particularly anti-LGI1 encephalitis, seizures may precede in weeks the development of cognitive and psychiatric symptoms. Faciobrachial dystonic seizures (FBDS) are very typical of anti-LGI1 encephalitis and their recognition is important to make an early diagnosis. New-onset refractory status epilepticus (NORSE) is a clinical presentation of epilepsy that occurs in patients without previous history of seizures. When NORSE is preceded by a febrile episode, the term FIRES (febrile infection-related epilepsy syndrome) is frequently used, particularly in the paediatric literature. FIRES is considered a subtype of NORSE that may occur at any age. Only a small number of patients with anti-NMDAR or anti-GABAbR encephalitis presents as NORSE. The term FLAMES (FLAIR-hyperintense Lesions in anti-MOG associated encephalitis with seizures) has been used to describe the encephalitis of some patients with MOG antibodies. The clinical presentation includes seizures associated with isolated or predominantly unilateral cortical hyperintense lesions in FLAIR MRI images.

In this chapter we describe different types of movement disorders that associate with autoimmune encephalitis, and the antibodies more frequently involved. In children the most common disorders are Sydenham chorea and anti-NMDAR encephalitis. Abnormal movements occur in ~80% of patients with anti-NMDAR encephalitis and include multiple different types such as chorea, oromandibular dystonia, stereotypies, opistotonus, catatonia, or myorhythmia. Children who develop anti-NMDAR encephalitis as a complication of previous herpes simplex viral encephalitis present prominent generalized chorea or choreoathetosis. In adults the most frequent autoimmune neurological disease that associates with movement disorders is anti-IgLON5 disease. More than 80% of patients this disease develop at least one type of movement disorder; gait instability or ataxia associated with craniofacial dyskinesias or generalized chorea are the most common combination of movement disorders. Hyperekplexia is a major manifestation of progressive encephalomyelitis with rigidity and myoclonus (PERM), which is usually associated with glycine receptor antibodies; some patients with similar symptoms have DPPX antibodies. Autoimmune chorea in adults may also be a paraneoplastic manifestation of small-cell lung cancer and CRMP5 antibodies. The most common paroxysmal abnormal movement of autoimmune origin is faciobrachial dystonic seizures associated with LGI1 antibodies. Patients with anti-CASPR2 encephalitis may have paroxysmal episodes of cerebellar ataxia that precede the encephalitis. Anti-CASPR2 encephalitis can also cause orthostatic myoclonus.