Given the high mortality and morbidity associated with untreated bacterial meningitis, the prompt diagnosis and treatment of patients with suspected bacterial CNS disease is an important objective for all clinicians. Unfortunately, few consensus guidelines exist to assist clinician decision making when treating adults for presumptive meningitis in the emergency room. In fact, a National Guideline Clearinghouse search using the term "meningitis" yielded only 1 guideline fully relevant to diagnosis and treatment of adult meningitis. This guideline outlines selection of antimicrobial therapy in the setting of acute bacterial meningitis. Lumbar punctures are required in the guideline's algorithm.4
Lumbar punctures help clinicians differentiate bacterial meningitis from aseptic meningitis or other benign illnesses, yet the procedure can be time-consuming and cause significant complications. Our study found that patients who underwent LP had 50% longer ED stays when compared with other patients in the ED. In addition, approximately 1 in 20 patients returned to the ED within 1 week complaining of headache. Other studies have shown headache to occur 10% to 30% of the time after LP.7
The development of a prediction rule to differentiate bacterial meningitis from aseptic meningitis before LP may be helpful to both clinicians and patients. Unfortunately, we found only one substantive study testing a prediction rule for bacteria meningitis that did not include CSF analysis. The prediction rule criteria include duration of the main complaint, vomiting, signs of meningeal irritation, cyanosis, petechia, altered consciousness, and elevated serum C-reactive protein. Unfortunately, the study was limited to children between the ages of 1 and 15.8
The development of a prediction rule to diagnose meningitis (bacterial or aseptic) before LP may also be helpful. At least one large retrospective study has shown, for example, that the "classic triad" of fever, stiff neck, and altered mental status occurs in about two thirds of adult patients with meningitis.1 Other studies have found the incidence of fever, neck stiffness, and altered mental status to be much lower, with only 21% to 51% of patients reporting these symptoms.9,10
In their large systematic review, Attia et al11 suggested that no single clinical examination finding could rule in meningitis, and only the absence of fever, neck stiffness, and altered mental status could effectively rule out meningitis in most adult patients. In our study, no combination of clinical criteria ruled out meningitis. In addition, of our 11 patients with meningitis, 7 had fever, but none reported the classic triad as symptoms.
Specific physical examination findings associated with meningitis have been reviewed in the literature. For example, several studies have shown that Kernig and Brudzinksi signs for meningeal irritation are unreliable predictors of meningitis.12 In addition, Uchihara and Tsukagoshi13 observed that accentuation of the headache after rapidly moving head side to side may be moderately predictive of abnormal CSF. Our study did not measure the predictive value of these signs.
Traditional teaching suggests that an elevated CSF cell count (normal, <5 cells/mm3), markedly elevated CSF protein (normal, 9-58 mg/dL), a decreased CSF glucose (normal, 45-80 mg/dL), and a PMN predominance greater than 24 hours from the onset of illness can help predict bacterial meningitis.14 Other authors suggest that benchmarks such as these unreliably differentiate bacterial meningitis from aseptic meningitis.6,15-17 In their comprehensive review, Fitch and van de Beek state, "despite multiple retrospective models using logistic equations and other mathematical modeling, none (of the models predicting bacterial CNS disease) have proved robust enough for widespread clinical practice."5 In our study, CSF findings such as pleocytosis and lymphocytic predominance were strongly associated with meningitis. This is not surprising given the predominance of viral etiologies of meningitis in our cohort which are associated with lymphocytic predominant CSF.
The causative agents of meningitis in our study were very different from standard textbook descriptions of meningitis. For example, there were no confirmed cases of meningococcal or pneumococcal meningitis, 2 agents commonly reported in the literature.5,18 In addition, there was 1 case of coagulase-negative S. aureus, which is a rare cause of bacterial meningitis. It is unclear whether this culture positive case was due to a skin contaminant. Finally, 1 of 10 patients in the study was HIV positive. Because only 2 of the 11 confirmed cases of meningitis were from HIV-positive patients (1 syphilis and 1 C. neoformans), the overall impact of HIV on the study results was likely minimal.
Our findings are consistent with research by Powers, who reviewed LPs during a 2-year period at the University of Virginia in Charlottesville. Of 104 LPs, Powers19 reported only 1 case of bacterial meningitis and 13 cases of viral meningitis or encephalitis. In our study, nearly one third (27%) of the confirmed cases were treatable with antiviral agents, suggesting the need for adding antiviral agents to the standard regimen when treating presumptive meningitis on adults in the ED.
It is important to note the role antibiotics played in our study. The sensitivity of a gram stain deceases by as much as 20%, and the diagnostic yield of CSF culture is similarly decreased with previous antibiotic use.20,21 In our study, 27 (16.4%) patients received antibiotics before LP, suggesting that some cases of meningitis were unconfirmed. However, the incidence of antibiotic use was distributed evenly between abnormal and normal CSF samples (16.7% and 16.3%, respectively), suggesting that the impact of antibiotic use before LP was minimal.
Limitations for this study include the small sample size and its retrospective nature. Reliance on retrospective review of electronic notes could have led to misclassification bias, and LPs done primarily for subarachnoid hemorrhage could have been identified as meningitis, or vice versa. If the LP was not documented, cases would have been missed on the database search. Likewise, cases of meningitis that were missed because an LP was not done could not be identified by this study.
The administration of antibiotics before LP could have resulted in false-negative LP results. In addition, at least 1 of the CSF culture-positive cases may have been a contaminant. The period of the study excluded winter months raising the possibility that the CSF samples studied underestimate certain pathogens such as enteroviruses. Finally, this study may not be generalizable to community settings because 10% of the study population was HIV positive.
In this study of 164 adult LPs performed for possible meningitis, no clinical criteria were identified that could select which adult ED patients would not need an LP because the likelihood of meningitis is low. The absence of fever, neck stiffness, and altered mental status did not rule out adult meningitis. In addition, more research may be needed to evaluate the need for adding antiviral agents to the standard regimen when treating presumptive meningitis on adults in the ED.
More research is needed to risk stratify adult patients and improve the utilization of LPs in the ED. Although nearly one third of LPs were abnormal, no cases of pneumococcus or meningococcus were identified. Considering the discomfort, time, and complications associated with an LP and considering over two thirds of LPs were completely normal, improved clinical guidelines to better select patients for LPs would be clinically useful.
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