Unraveling the enigma of new-onset refractory status epilepticus: a systematic review of aetiologies.

Background New-onset refractory status epilepticus (NORSE) is a clinical presentation, neither a specific diagnosis nor a clinical entity. It refers to a patient without active epilepsy or other pre-existing relevant neurological disorder, with a new onset refractory status epilepticus without a clear acute or active structural, toxic, or metabolic cause. This study reviews the currently available evidence about the aetiology of patients presenting with NORSE and NORSE-related conditions. Methods We systematically searched for clinical trials, observational studies, case series, and case reports including patients who presented with NORSE, febrile infection-related epilepsy syndrome, or the infantile hemiconvulsion-hemiplegia and epilepsy syndrome. Results Four hundred and fifty records were initially identified, of which 197 were included in the review. The selected studies were retrospective case-control (n=11), case series (n=83), and case reports (n=103) and overall described 1334 patients both of paediatric and adult age. Aetiology remains unexplained in about half of the cases, representing the so-called "cryptogenic NORSE". Among adult patients without cryptogenic NORSE, the most often identified cause is autoimmune encephalitis, either non-paraneoplastic or paraneoplastic. Infections are the prevalent aetiology of paediatric non-cryptogenic NORSE. Genetic and congenital disorders can have a causative role in NORSE, and toxic, vascular, and degenerative conditions have been also described. Conclusions Far from being a unitary condition, NORSE is a heterogeneous and clinically challenging presentation. The development and dissemination of protocols and guidelines to standardize diagnostic work-up and guide therapeutic approaches should be implemented. Global cooperation and multicentre research represent priorities to improve the understanding of NORSE.