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period. Subtherapeutic antiepileptic drug levels are one of the most common
causes of seizures in this population. The presence of fever may indicate that a
febrile seizure has occurred or, if normal consciousness is not regained, that the
patient has contracted a CNS infection such as meningitis or encephalitis (see
Chapters 94 Infectious Disease Emergencies and 97 Neurologic Emergencies ).
The new onset of afebrile generalized seizures requires a more thorough
evaluation, as detailed in Chapter 72 Seizures .
Infection
Coma-inducing infections of the CNS may involve large areas of the brain and
surrounding structures, as in meningitis or encephalitis, or they may be confined
to a smaller region, as in the case of cerebral abscess or empyema (see Chapter 94
Infectious Disease Emergencies ). The incidence of bacterial meningitis due to
Haemophilus influenzae , Streptococcus pneumoniae and Neisseria meningitidis
has diminished among vaccinated children, but these infections still occur in
unvaccinated and undervaccinated patients, and in the immunocompromised.
Lyme disease is now present throughout the United States, and is a common
cause of meningitis. Meningitis may also be caused by viral (enteroviruses,
herpes), fungal (Candida, Cryptococcus ), mycobacterial (tuberculosis), and
parasitic (cysticercosis) organisms. These nonbacterial infections usually have a
slower onset of symptoms.
Encephalitis, or inflammation of brain parenchyma, may also involve the
meninges (see Chapter 94 Infectious Disease Emergencies ). It occurs most
commonly as a result of viral infection or immunologic mechanisms. Mumps and
measles were common causes before immunizations against these diseases, and
they still occur in unimmunized individuals or in individuals in whom immunity
has waned. Varicella encephalitis occurs 2 to 9 days after the onset of rash. The
incidence of arthropod-borne encephalitides varies by geographic location but
usually peaks in late summer and early fall. The herpes simplex virus (HSV)
remains the most common devastating cause of encephalitis, causing death or
permanent neurologic sequelae in the majority of patients. Beyond the neonatal
period, HSV affects the temporal lobes most severely, leading to seizures and

parenchymal swelling, which can cause uncal herniation.
Focal CNS infections include brain abscesses, subdural empyemas, and
epidural abscesses (see Chapter 94 Infectious Disease Emergencies ). Brain
abscesses occur most often in patients with chronic sinusitis, chronic ear
infection, dental infection, endocarditis, or uncorrected cyanotic congenital heart
disease. Subdural empyema also occurs as a result of chronic ear or sinus