Low cerebrospinal fluid beta-amyloid 42 in patients with acute bacterial meningitis and normalization after treatment.

CSF-A beta 42 may be a marker of Alzheimer's disease (AD). A decreased level of CSF-A beta 42 is consistently found in AD and has been suggested to be related to the deposition of amyloid plaques in the brain. However, low CSF-A beta 42 levels have also been found in disorders devoid of plaques, for instance Creutzfeldt-Jakob disease. To examine if the level of A beta 42 in CSF is related to inflammatory processes, we studied CSF-A beta 42 levels in eight patients with acute purulent bacterial meningitis, 10 patients with acute viral meningitis and 18 age-matched controls. In acute purulent bacterial meningitis, the CSF-A beta 42 level was markedly reduced (28% of that in controls, P<0.0001), whereas no change was found in viral meningitis. After successful treatment of bacterial meningitis, the CSF-A beta 42 level increased (P<0.05 compared to baseline) and did no longer differ from that in controls (ns). The decrease could not be explained by interference with high protein levels, since addition of increasing volumes of serum did not influence the CSF-A beta 42 levels. Our findings suggest that the reduction in CSF-A beta 42 found in bacterial meningitis is not a direct consequence of the inflammatory process. The cause may be disturbance of the clearance of A beta 42 from the brain.