Acute Necrotizing Encephalopathy (ANE) is a rare disease characterized by high morbidity and mortality rates. This case report provides a comprehensive overview of the clinical symptoms, diagnostic processes, and imaging findings associated with ANE. It also discusses treatment strategies and patient outcomes, enhancing the understanding of this condition.

This case involves a 35-month-old female who was born at term without complications, coming from a non-consanguineous marriage. Her neurodevelopment was age appropriate.

She had a 5-day history of fever, respiratory symptoms, was admitted to the hospital in January 2019 because of altered consciousness, and dizziness. She could open her eyes spontaneously, had nystagmus, single movements after painful stimulation, and no verbal response. Reflexes were symmetrically exaggerated. A positive Babinski sign bilaterally.

Brain MRI - bilateral lesions in the external capsule, thalamus, and brainstem.

CBC, CRP, urine analysis, electrolytes, liver, and renal functions - normal. CSF-Elevated protein, no cytosis. EEG - diffuse delta activity.

Differential diagnoses: infectious (Mycoplasma, CMV, HSV), and non-infectious (anti-NMDA receptor encephalitis, mitochondrial disease, disruption of thiamine metabolism) etiologies. Empiric treatment - Acyclovir before the serology results - negative for infection markers. After that, IV Ig therapy was initiated for 5 days and Biotin and Thiamine were added to the treatment.

The patient’s general condition improved, became alert, came into emotional contact, spoke with sentences, followed instructions, and had no focal deficits.

WES - RANBP2 gene AD heterozygous mutation (2q12.1q13), responsible for Acute Necrotizing Encephalopathy.

Nowadays, she is 8.5 years old, her motor development is normal, speaks with sentences, and has mild learning difficulties, problems with concentration and memory. She has had a fever and viral infection but had no encephalopathy since 2019.

Clinicians should consider ANE in the differential diagnosis for patients exhibiting bilateral external capsule, thalamus, and brainstem lesions with encephalopathy. Early recognition is crucial for appropriate management and improved prognosis.