A 30-year-old man has normal blood glucose of 90 mg/dL but his CSF glucose is 20 mg/dL (CSF:plasma ratio 0.22; normal ≥0.6). CSF protein is 80 mg/dL. CSF opening pressure is 120 mmH2O (normal). What is the MOST likely diagnosis, and which transport mechanism is impaired?
- A Bacterial meningitis consuming glucose by local glycolysis; GLUT1 transporter function is secondarily reduced by bacterial neuraminidase
- B GLUT1 deficiency syndrome (De Vivo disease): impaired GLUT1-mediated glucose transport across choroid plexus and BBB ✓
- C Viral encephalitis with increased blood-brain barrier permeability causing glucose dilution
- D Subarachnoid hemorrhage with red blood cell glycolysis consuming CSF glucose
Explanation
A CSF:plasma glucose ratio below 0.4 in the absence of markedly elevated CSF white cells, normal opening pressure, and with modestly elevated protein is the hallmark of GLUT1 deficiency syndrome (De Vivo disease). GLUT1 is the primary glucose transporter expressed on blood-brain barrier endothelium and choroid plexus epithelium; its deficiency selectively impairs glucose entry into the CNS while systemic blood glucose remains normal. This causes cerebral energy deficiency manifesting as seizures, developmental delay, and movement disorders. Bacterial meningitis (option A) causes hypoglycorrhachia through metabolic consumption and may have some GLUT1 downregulation, but presents with high WBCs, high protein, and usually an infectious context. Viral encephalitis (option C) causes mild protein elevation but not profound hypoglycorrhachia. SAH (option D) presents with xanthochromia and red cells.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.