Diagnostic Challenges in Atypical Rasmussen’s Encephalitis (RE) Presenting with Brainstem Involvement

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Objective To report on the diagnostic challenges and positive response to early surgical management of a patient with atypical RE with brainstem pathology and highlight the challenges of immunomodulation. Background Rasmussen’s encephalitis is a rare cause of intractable focal epilepsy in the pediatric population. It is associated with progressive cognitive decline and hemiparesis with radiographic findings of unilateral cortical atrophy. Hemispherectomy is the only curative option for treating these patients' seizures. Design/Methods Case Report. Results A 9-year-old girl presented for evaluation of staring spells and ataxia. Brain MRI showed non-enhancing lesions in the pons and left middle cerebellar peduncle. EEG revealed focal seizures originating in the right temporal lobe. CSF was positive for oligoclonal bands and an elevated IgG index; serum autoimmune encephalopathy panel was negative. Meeting diagnostic criteria for probable antibody-negative autoimmune encephalitis, immunomodulation was tried with corticosteroids, plasmapheresis, IVIG, and rituximab. Seizures were uncontrolled despite the optimization of three anti-seizure medications. Within a few months, her symptoms progressed as she developed right sixth cranial nerve palsy, left hemiparesis, and epilepsia partialis continua involving her left leg. Repeat MRI showed signs of right cortical atrophy and a new right frontoparietal lesion. The patient eventually had a brain biopsy demonstrating lymphocyte (CD8+ T-cell) predominant inflammatory infiltrates, establishing the diagnosis of Rasmussen’s encephalitis. She underwent a right functional hemispherectomy and had an improvement in her seizure frequency while continuing anti-seizure medications. Conclusions Brainstem involvement in Rasmussen’s encephalitis is very rare and has been infrequently reported in the literature. Early surgical hemispherectomy is beneficial, as patients have a better chance of achieving seizure freedom than with pharmacologic treatment alone. One should consider Rasmussen’s encephalitis in the differential diagnosis for seronegative autoimmune encephalitis, particularly in cases with minimal clinical response to immune-modulating therapies.

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