A patient with bacterial meningitis has CSF findings: protein 200 mg/dL, glucose 20 mg/dL (serum glucose 80 mg/dL), cells 1500/mm3 (90% neutrophils). The CSF:serum glucose ratio is 0.25. Which factor most directly causes the low CSF glucose in bacterial meningitis?
- A Increased glucose consumption by bacteria and inflammatory cells combined with impaired GLUT-1 transporter-mediated glucose transport across the inflamed BBB ✓
- B Reduced cerebral blood flow causing ischaemic impairment of the choroid plexus glucose transport
- C Elevated CSF lactate competitively inhibiting GLUT-1 transporters, reducing glucose entry
- D Serum hypoglycaemia in sepsis patients causing secondary CSF hypoglycorrhachia
Explanation
CSF hypoglycorrhachia (low CSF glucose, CSF:serum ratio <0.5, or absolute glucose <45 mg/dL) in bacterial meningitis results from two concurrent mechanisms: (1) direct consumption of glucose by the large number of bacteria and activated neutrophils (glycolysis and metabolic demand) and (2) inflammation-mediated impairment of GLUT-1 (facilitated glucose transporters) in both the choroid plexus epithelium and the blood-brain barrier, reducing active glucose transport into the CSF. In the given case, serum glucose is 80 mg/dL (normal), so serum hypoglycaemia (option D) does not apply. Reduced CBF (option B) and lactate competition (option C) are not the primary mechanisms.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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