# Seronegative Immune-Mediated Cerebellar Ataxia in Children: Autoimmune Encephalitis Spectrum Disorder or a Distinct Entity?

## TL;DR

This paper discusses a rare condition in children called seronegative immune-mediated cerebellar ataxia and explores whether it is a form of autoimmune encephalitis or a distinct disorder.

## Contribution

The paper introduces the use of TIIF/IHC and potential biomarkers like NfL and GFAP for diagnosing pediatric seronegative IMCA.

## Key findings

- A 2.5-year-old girl showed improvement with corticosteroid therapy for seronegative IMCA.
- TIIF/IHC detected intracellular signals in Purkinje cells, supporting the diagnosis.
- NfL and GFAP are suggested as potential biomarkers for this condition.

## Abstract

Pediatric seronegative immune-mediated cerebellar ataxia (IMCA) remains a poorly defined and often under-recognized diagnosis, particularly in young children, where symptoms are frequently misattributed to self-limited post-infectious processes. We report the case of a 2.5-year-old girl who presented with acute-onset ataxia (mSARA score: 14). Cerebrospinal fluid analysis revealed pleocytosis and positive oligoclonal bands, while serial brain imaging and extensive autoantibody panels were unremarkable. However, indirect immunohistochemistry (TIIF/IHC) demonstrated a positive intracellular signal in cerebellar Purkinje cells, supporting the diagnosis of isolated seronegative IMCA. The patient showed sustained clinical improvement with prolonged corticosteroid therapy (mSARA score: 1). To date, only a few similar cases have been reported in the literature. It remains unclear whether these presentations fall within the spectrum of autoimmune encephalitis (AIE) or represent a distinct pediatric phenotype, potentially expanding the age range of primary autoimmune cerebellar ataxia previously described in adults. We recommend incorporating TIIF/IHC into the diagnostic workup of both isolated and combined pediatric cerebellar ataxia syndromes to support diagnosis and guide individualized treatment. Additionally, neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) are emerging as promising biomarkers in this context and warrant further investigation.