1 Describe the most common signs and symptoms of acute meningitis syndrome

Fever, neck stiffness, and altered mental status are the classic triad, but they occur together only approximately 45% of the time. In a systematic review, 95% of patients had two of the three classic signs. The onset is hours to days, although historical detail may be limited if the patient’s sensorium is altered.

2 What is the pathophysiology of meningitis?

The pathogen gains entry via attachment on epithelial mucosal cells, endocytosis by dendritic cells, or direct vascular access. In the setting of bacterial meningitis, infection causes cytokine production and influx of inflammatory cells. The blood-brain barrier may have changes in permeability, allowing for protein entry in addition to inflammatory cells and fluid. Vasculature initially vasodilates but then becomes stenotic with infiltration of inflammatory cells. This vasculitis can result in ischemia and/or infarction. Glucose metabolism is increased and transport across the blood-brain barrier possibly decreased.

3 What is the distinction between acute versus chronic meningitis?

Acute meningitis syndrome consists of fever, neck stiffness, and altered mental status with an onset of hours to days. Patients with acute bacterial meningitis may have rapid progression of signs and symptoms. This is in contrast to chronic meningitis, which is defined by presence of symptoms and abnormal cerebrospinal fluid (CSF) that persists for 4 weeks or more. The two syndromes have very distinct causes.

4 What host factors are important to consider regarding risk and cause for acute bacterial meningitis?

Factors such as age, immune deficiency or suppression, recent central nervous system (CNS) instrumentation, and possible exposures should be considered and will influence empirical therapy. See Table 34-1.

5 What are the most common causes of community-acquired acute bacterial meningitis in adults?

Table 34-2 includes the most common organisms in descending order based on case series with preferred antimicrobial therapy and suggested duration of treatment.

^{Table 34-2} Most Common Causes of Community-Acquired Bacterial Meningitis in Adults

MIC, Minimum inhibitory concentration; MSSA, methicillin-sensitive S. aureus; PCN, penicillin.

6 What is adequate empirical therapy while awaiting culture results?

Empirical therapy should reflect suspected pathogens on the basis of host factors as well as local antibiotic susceptibility patterns. For example, Streptococcus pneumoniae is commonly known to have resistance to penicillin. Some strains are also resistant to third-generation cephalosporins. As a result, empirical therapy for S. pneumoniae should include high-dose third-generation cephalosporin as well as vancomycin. Empirical therapy with third-generation cephalosporin is also suggested for Neisseria meningitidis. For Listeria monocytogenes, preferred treatment is ampicillin, although trimethoprim-sulfamethoxazole is another option if the patient is penicillin allergic. Thus in an adult older than 50 years, an initial empirical regimen including vancomycin, high-dose ceftriaxone, and ampicillin would be suggested to treat the most likely community-acquired pathogens.

In the event that a patient has undergone recent neurosurgical instrumentation and has risk for nosocomial pathogens, one would also want to include therapy directed at methicillin-resistant Staphylococcus aureus (MRSA) and resistant nosocomial gram-negative bacilli, such as Pseudomonas aeruginosa.

Risk factors that may additionally influence empiricism must be identified with each patient. Prompt and detailed history should be explored. Factors including exposures, such as contaminated food consumption, travel, and sick contacts should be identified. Presence of immune suppression should also be elicited. The type and degree of immune suppression, including medications, absence of spleen, advanced HIV, and administration of chemotherapy should be sought. Risk factors for nosocomial pathogens, including recent neurosurgical procedures, presence of a foreign body within the CNS (such as a ventricular drain), and trauma are also important to determine, as noted earlier.

7 When and to whom should steroids be administered?

Adults suspected of having bacterial meningitis should receive steroids before or with the administration of antibiotics. On the basis of a prospective, randomized, placebo-controlled trial, dexamethasone was shown to reduce morbidity and mortality in adults who received corticosteroid therapy before or at the same time as administration of antibiotics. This had the greatest benefit in patients with pneumococcal meningitis. The dose used in the study was 10 mg of dexamethasone every 6 hours for 4 days. Shorter durations and alternative dosing regimens have not been evaluated in adults.

8 What are the contraindications to lumbar puncture (LP)?

LP is critical to diagnostic evaluation. If clinical suspicion for meningitis exists, one should perform an LP. Conditions such as elevated intracranial pressure, mass lesion, uncorrected coagulopathy, and skin infection overlying intended puncture site are to be considered before LP.

9 When would one consider imaging before LP?

Most patients do not require imaging before LP. Computed tomography (CT) of the head should occur before LP if the patient has any signs or symptoms that suggest elevated intracranial pressure. These include new-onset neurologic deficits, new-onset seizure, and papilledema. Consideration should also be given to imaging in patients with moderate to severe cognitive impairment and immune compromise.

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