Use of cerebrospinal fluid lactic acid concentration in the diagnosis of fungal meningitis

A patient with a several year history of normal pressure hydrocephalus was found to have an infection owing to Cryptococcus neoformans. Cryptococcal infection was not suspected until typical cells were observed in a Wright's stained smear of cerebrospinal fluid (CSF). A review of past medical findings in this patient showed elevated CSF values for lactic acid and protein. This case prompted us to review the use of lactic acid as an indicator of fungal meningitis and compare it to other more commonly used nonspecific indicators of fungal meningitis, notably the concentrations of glucose and protein, and the number of leukocytes in CSF. In our institution, all 10 culturally proven cases of fungal meningitis, for which the lactic acid concentration in the CSF was available, were found to have an elevated lactic acid concentration (range 3.2 to 13.3 mmol per L vs normal range 0.8 to 2.8 mmol per L). No other nonspecific indicator was elevated in all 10 patients. In view of the poor sensitivity of stained smear or wet preparations and cultures, when less than five ml of CSF are used for culture, an elevated lactic acid value in a patient with or without signs of meningitis should raise the suspicion of fungal infection.