Comparison of Lumbar and Ventricular Cerebrospinal Fluid for Diagnosis and Monitoring of Meningitis.

Severe meningitis, especially basilar meningitis, can lead to hydrocephalus requiring external ventricular drain (EVD) placement. There are differences in cerebrospinal fluid (CSF) obtained from an EVD compared to a lumbar puncture (LP). Hence, it becomes difficult to compare LP and EVD samples for diagnosis and monitoring of meningitis. Recognizing these differences is important to properly treat and discontinue antibiotics. We report a case series of 6 patients with meningitis comparing EVD and LP CSF study analysis. In all 6 patients, CSF from LP was obtained before EVD placement by 1.7 days on average. Although corrected white blood cell (WBC) counts were elevated in CSF obtained from LP and EVD, the counts were significantly higher in LP CSF. Protein concentration in LP CSF was also significantly higher than EVD CSF. Glucose and red blood cells varied in both LP and EVD samples. Even though EVD CSF was obtained later in the clinical course than LP, slower circulation of CSF in lumbar space as compared to ventricles is likely the reason for a more sterile appearance of EVD CSF for the diagnosis of meningitis. It is important to recognize these differences as EVD CSF analysis for diagnosis of meningitis may lead to a missed diagnosis and false perception of significant improvement when monitoring response to treatment. One can consider repeating LP prior to discontinuation of antibiotics to properly determine the extent of improvement given EVD CSF sample appears more sterile in comparison. Larger studies are needed to confirm the above findings.