# Case Report: PET/CT assessment of immunomodulatory therapy in anti-IgLON5 encephalitis with sleep apnea

## TL;DR

This case report shows how PET/CT scans can help track treatment progress in a rare autoimmune brain disorder linked to sleep issues.

## Contribution

Demonstrates the use of 18F-FDG PET-CT to assess immunomodulatory therapy effects in anti-IgLON5 encephalitis.

## Key findings

- Abnormal FDG uptake in medulla oblongata and left temporal lobe confirmed anti-IgLON5 encephalitis.
- Immunomodulatory treatment improved symptoms and normalized metabolism in follow-up PET/CT scans.
- PET/CT imaging provides insights into disease mechanisms and treatment response in this rare condition.

## Abstract

Anti-IgLON5 disease is a rare autoimmune neurological disorder characterized by sleep disturbances, movement disorders, cognitive decline, bulbar symptoms, and respiratory dysfunction, with a complex interplay between autoimmunity and neurodegeneration. Recent studies have provided insights into its clinical manifestations, immunological mechanisms, and potential therapeutic approaches. However, there is limited research on the diagnosis of Anti-IgLON5 disease and the assessment of immunomodulatory treatment effects from a metabolic perspective by Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography-Computed Tomography (18F-FDG PET-CT). This case describes a 59-years-old male presented with 1-year history of recurrent insomnia, low mood, staring spells, dysphagia, and choking while drinking water. Initially misdiagnosed with a gastrointestinal disorder or mental illness. The diagnosis was confirmed by positive serum and cerebrospinal fluid (CSF) tests for anti-IgLON5 antibodies, and 18F-FDG PET-CT showed abnormal FDG uptake in the medulla oblongata and left temporal lobe. After treatment with immunoglobulin pH4, mycophenolate mofetil tablets and corticosteroids significantly improved his condition. Follow-up at 3 months showed normalized metabolism on 18F-FDG PET-CT and improved sleep architecture. This case emphasizes the significance of anti-IgLON5 encephalitis in the differential diagnosis of complex sleep disorders, while also providing new insights and experiences regarding the evaluation of immune-modulatory therapy in the treatment of anti-IgLON5 encephalitis through 18F-FDG PET-CT. Overall, anti-IgLON5 disease is a multi-systemic condition that requires further research to identify precise and effective therapeutic strategies. Our case highlights the potential utility of 18F-FDG PET-CT in elucidating disease mechanisms and guiding clinical management.