IgLON5 is a cell adhesion molecule of unknown significance. Recently, antibodies to this protein were found to be associated with a rare syndrome characterised by sleep disorder, bulbar dysfunction and movement disorder. The disease is progressive and can cause life threatening respiratory compromise. Postmortem findings are consistent with a neuronal tauopathy, linking a neurodegenerative process to this autoimmune condition. HLA-DRB1*10:01 and HLA-DQB1*05:01 haploptypes are susceptibility factors.

Case description: A 66-year-old woman with primary biliary cirrhosis was referred for neurological assessment with a 4-year history of excessive daytime somnolence, disturbed sleep, speech slurring, dysphagia and abnormal eye movements. She had been diagnosed with OSA and commenced on BIPAP. Symptoms progressed and the patient noted slow eye movements and eyelid drooping. She also developed involuntary limb movements and problems with balance. Examination showed slow horizontal and vertical saccades, dysarthria and generalised chorea. Immunotherapy was commenced. 

Routine laboratory investigations were normal. MRI brain showed chronic ischaemic changes only. CT TAP did not show any malignancy. Serum IgLON5 antibodies tested positive, titre 1:1000. 

Anti IgLON5 antibody syndrome is a recently described, rare, neurological disorder bridging autoimmune disease and neurodegeneration. The clinical profile is heterogenous: sleep disorder, gait difficulties, oculomotor abnormalities, bulbar dysfunction, chorea, and cognitive decline. There is evidence to suggest a sustained response can be achieved with immunotherapy in some cases but overall the response seems to be poor. The pathogenesis of this disease remains unclear.