Background/objective: The use of natalizumab (NAT) in multiple sclerosis (MS) may be complicated by progressive multifocal leukoencephalopathy (PML), a rare and life-threatening opportunistic brain infection. We aimed to analyze the course of MS after PML recovery together with the long-term outcome of NAT-associated PML (NAT-PML) in Austria. Methods: Retrospective study based on identification of cases in the nationwide Austrian MS treatment registry (AMSTR) and MS centers with review of patient records. The expanded disability status scale (EDSS) was used to measure neurological disability and outcome. Results: As of December 2022, we identified 15 NAT-PML cases in Austria; only 20% occurred after 2016, when increased vigilance commenced. Two patients did not survive acute PML, and an additional patient died five years later, yielding a mortality rate of 20%. Seizures occurred exclusively in patients with pronounced EDSS increase. Gadolinium (Gd)-enhancement on brain magnetic resonance imaging (MRI) on PML suspicion was associated with minor changes of post-PML neurological disability. Long-term follow-up of up to 132 months (median 76 months) was available in 11/15. The overall median EDSS increased from 3.5 at pre-PML to 6.5 at the last assessment. Regarding inflammatory MS-related disease activity during the observation period, one single individual experienced an MS relapse and another patient had two Gd-enhancing brain lesions. Three patients converted to progressive MS within three years from PML and the EDSS further increased in 6/11. Conclusions: The number of NAT-PML cases is decreasing over time. While many patients accumulated severe persistent neurological deficits compared to pre-PML, inflammatory MS-related disease activity after PML recovery was rare.

Background/Objectives: Anti-IgLON5 disease is a neurological disorder characterized by the presence of autoantibodies directed against the neuronal cell adhesion protein IgLON5. Pathophysiology involves both autoimmune inflammation and neurodegenerative processes. The most common causes of death are sudden death, central hypoventilation, dysphagia, and aspiration. However, the high rate of largely unclear sudden deaths calls for further research in this area. Methods: We performed a systematic search of the literature on causes of death in anti-IgLON5 disease following the PRISMA guidelines. In addition, we present a new case that was followed up in our clinic until death. Results: Of 258 publications with anti-IgLON5 disease, 21 publications comprising 61 cases that reported the causes of death were included in the analysis. The most common cause of death was death due to complications at 36.1%, followed by sudden death, accounting for 32.8% of the cases. Other causes include respiratory, cardiac, and unknown causes. The patient presented here as a case report was also diagnosed with cardiac amyloidosis and died from a cardiac cause of sudden death. Conclusions: Sudden death in anti-IgLON5 disease is one of the most common causes of death in the literature. A progressive neurodegenerative process in the brain stem causing central hypoventilation is generally assumed as a major causative factor. The case reported here had concomitant cardiac amyloidosis, which may raise the question as to whether unrecognized cardiac causes, which are not routinely screened for in this population, might represent another cause of sudden death, which would have important therapeutic implications.