To describe movement disorders (MD) in a large nationwide cohort of autoimmune encephalitis (AIE) and paraneoplastic neurological syndromes (PNS).

Although a large variety of MD has been described in different antibody-associated syndromes, frequency and clinical course of specific MD remains unknown for most antibodies. This knowledge is important to aid in early diagnosis and develop rational antibody testing strategies.

We identified 1,140 patients (56% female, 58/1,140 [5%] <18 years, mean age 56 years [range 1-87]). The most common antibody targets were HuD (n=212, 19%), NMDAR (n=189, 17%), LGI1 (n=187, 16%) and high-concentration GAD65 (n=135, 12%). MD were present in 459 patients (42%) and were the predominant or first symptom in 56% and 50% of these, respectively. Cerebellar ataxia was the most common (n=235, mainly Yo and GAD65), followed by dyskinesia (n=61, mainly NMDAR), myoclonus (n=51, mainly NMDAR) and stiff-person syndrome (n=51, mainly GAD65). Patients with Yo- and DNER/Tr-antibodies presented (almost) exclusively with MD (cerebellar ataxia), while the lowest MD frequency was observed in anti-GABA_BR (6/56, 11%) and anti-LGI1 (19/181, 10%; excluding faciobrachial dystonic seizures). Furthermore, we identified MD associations not previously reported, i.e. chorea/dystonia (n=1) and catatonia (n=1) in anti-KLHL11-associated encephalitis, chorea (n=2) in anti-GlyR encephalitis and episodic ataxia in anti-LGI1 and anti-GAD65-associated neurological syndrome (both n=1).

MD are common in antibody-associated AIE/PNS, occurring in 42% of patients, with varying frequencies depending on specific subtype and antibody. MD can be the first, predominant and even only manifestation of these diseases. Additionally, we also describe some novel antibody-MD associations. Antibody-associated neurological diseases should be in the differential diagnosis of new-onset MD and we provide recommendations for rational antibody testing in different phenotypes.