Infections of the central nervous system (CNS) in children continue to pose a diagnostic and therapeutic challenge to clinicians. Because of the plethora of bacterial, viral, fungal, and protozoan agents capable of infecting the CNS, it is not possible to discuss them all within the context of this chapter. As such, this chapter focuses on agents most likely to be encountered by hospitalists in the course of their activities.
Simply defined, meningitis is an inflammation of the membranes (i.e. arachnoid, dura, and pia mater) surrounding the brain and spinal cord. Encephalitis involves an inflammatory process of the cerebrum. Although it is common to discuss each as separate entities, in many cases, particularly with viral infections of the CNS, they occur together as meningoencephalitis.
Over the last three decades the number of cases of bacterial meningitis in the United States has steadily declined from 10,000 to 20,000 cases per year to approximately 4100 cases annually from 2003 to 2007.1,2 In large part as a result of the development of conjugate vaccines against Haemophilus influenzae type B (Hib) and Streptococcus pneumoniae, Neisseria meningitidis has become the leading cause of bacterial meningitis in children.3 Before the introduction of conjugate vaccines for the prevention of childhood infections caused by Hib, this agent was the principal cause of bacterial meningitis in the United States, as well as invasive bacterial infections.4 Inclusion of Hib conjugate vaccines in the routine immunization schedule of children has resulted in the virtual disappearance of invasive Hib disease in children younger than 5 years5 and a fall in the incidence of Hib meningitis from 2.9 to 0.2 cases per 100,000 population. Coincident with this decline has been a shift in the median age of all patients with meningitis from 15 months to 41.9 years.1,4
As a result of the licensure of the 7-valent and 13-valent (serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 23F) pneumococcal conjugate vaccines in 2000 and 2010, respectively, a significant decrease in the reported cases of S. pneumoniae invasive disease has been observed.6 In one report, the incidence of invasive pneumococcal disease decreased by 50% the year following introduction of the 13-valent pneumococcal conjugate vaccine.7
The possible causes of bacterial meningitis are numerous (Table 98-1) and depend on such factors as age, immunization status, and underlying clinical condition (e.g. inherited or acquired immunodeficiency states, ventriculoperitoneal shunts, cochlear implants, cerebrospinal fluid [CSF] leaks). Immunocompromised hosts deserve special consideration when meningitis is suspected. Opportunistic infections caused by Cryptococcus neoformans, Toxoplasma, tuberculosis, and fungi (e.g. Aspergillus species) must be considered.
TABLE 98-1Differential Diagnosis ||Download (.pdf) TABLE 98-1 Differential Diagnosis