Neurological profiles beyond the sleep disorder in patients with anti-IgLON5 disease

Purpose of review Anti-IgLON5 disease is a novel entity characterized by a distinctive sleep disorder associated with a variety of neurological symptoms, antibodies against IgLON5, and pathological findings of neuronal tauopathy. The characteristic sleep disorder occurs in most patients, but other neurological symptoms are also important because they can be the presenting and most disabling problem and mimic other conditions. This review focuses on nonsleep neurological symptoms and presentations of anti-IgLON5 disease. Recent findings Apart from sleep problems, the most frequent neurological symptoms in anti-IgLON5 disease are bulbar dysfunction and gait abnormalities. Other symptoms include movement disorders like chorea or abnormal orofacial movements, oculomotor abnormalities, cognitive impairment, and symptoms of nervous system hyperexcitability. All these symptoms can present in different combinations and severity leading to distinct clinical phenotypes beyond the sleep disorder: bulbar syndrome; syndrome resembling progressive supranuclear palsy; cognitive impairment, sometimes with chorea, mimicking Huntington disease; gait ataxia; and stiff-person-like syndrome. Summary These clinical presentations may suggest degenerative or other neurological disorders, but anti-IgLON5 disease has to be considered, and confirmed by the detection of IgLON5 antibodies, when the criteria for the diagnosis of the initially suspected disorders are not fulfilled, confirmatory laboratory tests are negative, and significant sleep problems are present.