Familial recurrent febrile encephalopathy: an atypical presentation of acute necrotising encephalopathy type 1 with unusual neuroimaging findings.

Acute necrotising encephalopathy type 1 (ANE1) is a rare, autosomal dominant disorder caused by mutations in the RANBP2 gene, characterised by recurrent episodes of encephalopathy triggered by febrile illness. The hallmark neuroimaging feature typically involves bilateral symmetric thalamic lesions. Atypical findings, either clinical or neuroimaging-wise, can pose significant diagnostic challenges. We report one such case of an early adolescent boy with a strong family history of recurrent febrile encephalopathies, who presented with his first episode of febrile illness associated with neurological deterioration. MRI imaging revealed signal changes in the pons and the external capsule. The strong family history of neurological disease made us consider a genetic aetiology. Exome sequencing identified a pathogenic RANBP2 variant. The child was started on steroids along with symptomatic therapy and had significant clinical improvement. This report highlights the atypical neuroimaging findings in the patient with RANBP2-related disorder.