171 - Meningitis, Encephalitis, and Brain Abscess

A 10-year review (1998 to 2007) of 3188 cases of bacterial meningitis noted that S. pneumoniae accounted for the greatest proportion of cases (58%), followed by group B. streptococcus (18.1%), N. meningitides (13.9%), H. influenzae (6.7%), and L. monocytogenes (3.4%). Among infants less than 3 months of age, group B Streptococcus and gramnegative rods account for most cases of ABM. After 3 months of age, S. pneumoniae and N. meningitidis become the predominant pathogens. L. monocytogenes is primarily seen in infants less than 1 month of age, in adults more than 50 years old, and in immunocompromised patients. Staphylococcus aureus is acquired mainly nosocomially and occurs • There is significant overlap among the initial clinical presentations of meningitis, encephalitis, and brain abscess. • The four most common bacteria responsible for adult bacterial meningitis are Streptococcus pneumoniae, Neisseria meningitides, Haemophilus influenzae type B, and Listeria monocytogenes. Group B Streptococcus remains the predominate cause of meningitis in infants less than 2 months of age. • The classic constellation of fever, neck stiffness, headache, and change in mental status are seen in less than 50% of cases of acute bacterial meningitis. • Cranial computed tomography (CT) scan, prior to lumbar puncture, is recommended in patients with a history of immunocompromised state, history of central nervous system (CNS) disease, new-onset seizure, abnormal neurologic examination, papilledema, altered mental status, or altered level of consciousness. • Empiric therapy in patients with high clinical suspicion for CNS infection should not be delayed for neuroimaging or lumbar puncture. • Although epidemiologic clues and assessment of risk factors should be sought in all patients with encephalitis, herpes simplex virus and arboviruses remain the most common causes of nonepidemic and epidemic outbreaks of encephalitis, respectively, in the United States. • Acyclovir should be initiated in all patients with suspected encephalitis, pending the results of diagnostic studies. • Risk factors for the development of intracranial abscess include inadequately treated subacute or chronic ear, nose, mastoid, and dental infection; endocarditis; congenital heart disease; and having undergone neurosurgical procedures. • Patients with intracranial abscess often present with mild headache symptoms in the weeks to months prior the emergency department visit. The classic triad of fever, headache, and focal neurologic deficit is seen in less than 20% of patients with brain abscess. KEY POINTS