Objective: We assessed the seropositivity rate of anti-IgLON5 antibodies in a real-world tertiary movement disorders cohort and are conducting a systematic review of published cases to examine the performance of standard diagnostic criteria in excluding anti-IgLON5 disease that may mimic idiopathic neurodegenerative syndromes.

Background: Anti-IgLON5 disease is a rare but potentially treatable disorder that frequently presents with movement abnormalities and may mimic idiopathic neurodegenerative syndromes, including atypical parkinsonism such as progressive supranuclear palsy (PSP) or multiple system atrophy (MSA), frontotemporal syndromes with stereotypies, and Huntington-like chorea.

Method: We conducted a retrospective analysis of records from 2022 to 2025 at a tertiary neurological clinic. Patients tested for anti-IgLON5 antibodies were identified from laboratory records. We aim to perform a comprehensive review of case reports of movement disorder phenotypes reported in the literature to occur in association with anti-IgLON5 disease.

Results: We identified 140 patients with movement disorders who underwent anti-IgLON5 testing in our laboratory. Clinical phenotypes included PSP (n=37), MSA (n=16), corticobasal syndrome (n=2), atypical-atypical parkinsonism (n=16), undetermined parkinsonism (n=32), cerebellar disorders (n=4), higher-level gait disorder (n=3), stereotypies (n=7), chorea (n=8), and various other presentations (n=13). Anti-IgLON5 antibodies were negative in all 140 samples, including one equivocal case from the atypical-atypical parkinsonism group, which was interpreted as a false-positive result. These findings suggest that although anti-IgLON5 disease can phenotypically overlap with a broad range of movement disorders, seropositivity in unselected patients without strong clinical suspicion appears to be uncommon. We aim to evaluate for clinical features that suggest a diagnosis of IgLON5-disease in the presence of movement disorder phenotypes.

Conclusion: Anti-IgLON5 seropositivity was rare in this tertiary movement disorders cohort. Taken together with preliminary review results, our findings support a targeted rather than routine testing strategy: anti-IgLON5 antibody screening may be most useful when atypical movement disorder phenotypes are accompanied by additional features that raise suspicion for anti-IgLON5 disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/anti-iglon5-testing-in-movement-disorder-clinical-practice-observational-cohort-study-and-systematic-review/