Lyme Versus Aseptic Meningitis: How Can You Tell the Difference?

The similarities in CSF findings in a patient with lyme meningitis and viral meningitis can make diagnosing the former difficult, especially if the history for lyme is not obtained. Yet, missing this diagnosis can potentially lead to all kinds of complications. Cohn et al. (doi: 10.1542/peds.2011-1215) test a clinical prediction rule called the “Rule of 7’s” to help determine if lyme meningitis could be possible in their interesting study being released online this week. What is the “Rule of 7’s”? It classifies children as being at low-risk for lyme if all of the three criteria are met – less than 7 days of headache, less than 70% of the CSF white cells are mononuclear cells, and no sign of 7th nerve palsy, which can be characteristic of lyme disease. The authors used a multicenter retrospective cohort to test this rule and found it extremely useful in ruling out lyme meningitis. Of course, a prospective evaluation of this rule is the next step, but you won’t be ticked off using the rule now if you are faced with determining if one of your patients has lyme disease.