Case Presentation: A 32-year-old male developed acute neurological deterioration during descent from Tilicho Lake (4,919 m) in the Annapurna region of Nepal. After rapid ascent from Besisahar (760 m) to Khangsar (3,750 m) in one day and further ascent to Tilicho Base Camp (4,140 m), he experienced severe headache, vomiting, dizziness, and progressive disorientation. While descending, he became ataxic, lost consciousness, and had urinary incontinence.

At the aid post, his oxygen saturation was 35% on room air and GCS was 8 (E2V2M4). He had no fever, pulmonary findings, or focal neurological deficits. Based on rapid ascent history, neurological signs, and absence of pulmonary edema, HACE was clinically diagnosed. Immediate treatment with supplemental oxygen and intramuscular dexamethasone (8 mg) resulted in gradual recovery of consciousness within 4–5 hours. His transient visuospatial disorientation and slurred speech resolved completely with descent and continued oxygen therapy.

HACE represents a preventable but potentially fatal hypoxic encephalopathy. Neurologists should recognize it as a neurocritical emergency, particularly as high-altitude exposure becomes more common through rapid vehicular ascent. Rapid descent, prompt administration of dexamethasone and oxygen can be lifesaving.