The un-ending saga of Seronegative autoimmune encephalitis

<p><strong>Objective:</strong> To characterize the clinical presentation, diagnostic challenges, neuroimaging findings, and treatment response in patients with seronegative autoimmune encephalitis (AIE) presenting as new-onset refractory status epilepticus (NORSE) and to assess the utility of fluorodeoxyglucose positron emission tomography (FDG-PET) and electroencephalogram (EEG) in diagnosis<br />and disease monitoring.<br /><strong>Background:</strong> NORSE is a life-threatening condition that often arises in the setting of AIE. While seropositive AIE has established diagnostic criteria, seronegative AIE remains a diagnostic challenge due to the absence of autoantibodies and non-specific findings on conventional investigations.<br /><strong>Methods:</strong> This is a prospective case series of four patients with seronegative AIE presenting as NORSE. Clinical history, cerebrospinal fluid (CSF) findings, magnetic resonance imaging (MRI), EEG, and FDG-PET results were analyzed. Immunotherapeutic interventions included intravenous immunoglobulin, corticosteroids, plasma exchange, rituximab, and tocilizumab.<br /><strong>Results:</strong> We present four patients with NORSE, characterized by challenging diagnoses due to negative antibodies in serological and CSF analyses. All patients exhibited normal MRI brain results. FDG PET revealed patterns of hypermetabolism or hypometabolism in sequential imaging. Therefore, indicating the potential function of FDG PET as an imaging biomarker in seronegative AIE.<br /><strong>Conclusion:</strong> Seronegative AIE presenting as NORSE remains a diagnostic and therapeutic challenge. Conventional MRI and CSF studies may be inconclusive, whereas FDG-PET and EEG provide valuable insights into disease activity. Early and aggressive immunotherapy can improve seizure control and clinical outcomes. Further research is needed to refine diagnostic criteria and treatment strategies for seronegative AIE.</p>