Background IgLON5 disease is a novel autoimmune tauopathy with diverse sleep and neurologic manifestations. Sleep disorder is a common initial presentation and may precede disease progression. Neurological symptoms frequently overlap with extrapyramidal syndromes, motor neuron disease and dementia. Diagnosis is confirmed by anti-IgLON5 IgG in CSF and/or serum. Strong HLA-DRB1*1001 and HLA-DQB1*0501 association supports autoimmune mechanism. Video-PSG is recommended to identify treatable

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... sordered breathing and parasomnia, present in up to 90% of cases. Treatment is empirical immunomodulation plus supportive cares. Mortality is high due to sudden cardiorespiratory arrest Methods Case reports. Progress to date Case 1 - 70-year-old male with recurrent respiratory arrests of apparent mixed aetiology and progressive dysphagia over 6 months. Preliminary investigations were unremarkable. Tracheostomy was inserted and immunoglobulin empirically commenced. IgLON5 antibodies were identified on CSF. HLA-DRB1*1001 and HLA-DQB1*0501 were positive. Pulse methylprednisolone and rituximab were administered. Intermittent respiratory failure subsided but bulbar symptoms progress. PSG showed NREM and REM parasomnia plus ataxic breathing. Case 2 - 58-year-old man presenting with altered level of consciousness. Examination findings included unsteady gait, strabismus, myoclonus, and truncal instability. IgLON5 IgG was identified on CSF. Sleep study showed ataxic breathing. Patient was treated with IVIG plus rituximab and CPAP. History is suspicious for evolving parasomnia. Intended outcome and impact IgLON5 disease is a newly recognized disorder with sleep manifestations. The ataxic breathing has not been well described. IgLON5 disease teases a novel association between autoimmunity and neurodegeneration.