Central Nervous System Infections

Case 1:

Harry, an 18-year-old man, recently moved into his new dormitory at a prestigious British college. A few weeks into the school year, he starts having headache and high fevers. His friend Ron notices that Harry isn’t acting quite like himself and that over the past day, Harry has become more somnolent and is muttering nonsensical phrases to himself. Which of the following about Harry’s case is true:

a.       Harry most likely has bacterial meningitis with Neisseria meningiditis, which can rapidly spread in crowded environments such as dorms and barracks.

b.      Harry’s case is most consistent with encephalitis given his altered mental status, personality changes and odd behavior.

c.       If Harry had been vaccinated prior to starting college, he would not have become ill.

d.       Harry does not need to receive a CT scan prior to undergoing a lumbar puncture.

Explanation:

The point of this question is to make sure you understand the difference between meningitis and encephalitis—on exams, this will be relatively easy to do (significantly altered mentation for >24 hours in duration should lean you towards encephalitis) but in reality, this can be tricky. Both conditions are life-threatening and typically present with fever and headache. Patients with meningitis may be uncomfortable, lethargic, or distracted by headache, but in general, their cerebral function remains normal. On the other hand, abnormal brain function is a distinguishing feature of encephalitis, and patients can present with altered mental status, motor or sensory deficits, altered behavior and personality changes, and speech or movement disorders. (Of note, seizures can be seen with meningitis and should not be considered definitive evidence of encephalitis.)

However, the line between the two can be blurred because of significant overlap (some patients may have both a brain parenchymal process—encephalitis—as well as a meningeal process.) Meningoencephalitis is also a commonly used term that recognizes the overlap in case the situation is unclear. The correct answer choice here is B.

In this case, Harry’s altered mental status (and possible encephalitis) definitely warrants a CT of the head prior to LP. Let’s talk about meningitis first…