THE CLINICAL CHALLENGE
Infections of the central nervous system (CNS) can be rapidly fatal and require prompt intervention in order to maximize good outcomes. Providers are forced to act quickly to provide treatment, often without knowing the exact underlying pathology. Many patients will have a nonspecific presentation with a wide differential diagnosis. Although fever is common in pathologies such as meningitis (inflammation of the meninges) or encephalitis (inflammation of the brain), it may not be present in other types of CNS infections, such as neurocysticercosis or opportunistic fungal infections in immunocompromised patients.
More than half of cases of bacterial meningitis in the United States are caused by Streptococcus pneumoniae
However, Neisseria meningitidis, Escherichia coli
, Haemophilus influenzae,
and Listeria monocytogenes
also represent frequently isolated bacterial species. Even with treatment, mortality is as high as 16%.2 Mycobacterium tuberculosis
also represents a common cause of meningitis worldwide, with as many as 1% to 2% of patients with active tuberculosis (TB) being affected by CNS infection. As with many CNS infections, meningitis secondary to M tuberculosis
is more frequently seen in patients with compromised immune systems, such as those afflicted by human immunodeficiency virus (HIV).
Viral meningitis is the most common CNS infection; it is generally associated with lower morbidity and mortality than bacterial meningitis. Enteroviruses are the most common infectious pathogens, particularly in warmer seasons. However, other important pathogens include herpes simplex virus (HSV), varicella-zoster virus (VZV), cytomegalovirus (CMV), Epstein-Barr virus (EBV), and HIV. Often, the exact pathogen is not identified. Owing to modern vaccination practices, rates of certain previously common etiologies of viral meningoencephalitis, such as measles and mumps, have decreased. Although viral infections are typically less severe and often have excellent outcomes, many features of bacterial and viral meningitis overlap, making the distinction between them difficult, especially at the onset of disease.
Certain fungal species can also invade the CNS. The most common being Cryptococcus neoformans,
followed by Coccidioides immitis
. Mucormycosis can also spread to the CNS; diabetic patients are at higher risk for this severe invasive infection. Other common invasive fungal species, such as Aspergillus
only rarely cause meningitis. Fungal CNS infections were previously found mainly in patients with HIV/acquired immunodeficiency syndrome (AIDS), but the
incidence has been increasing because of the greater numbers of patients on chronic immunosuppression for transplanted organs and autoimmune conditions.
The most common parasitic CNS infection worldwide is neurocysticercosis, mostly occurring in lower income countries.2
This is caused by ingestion of the larva of the tapeworm Taenia solium
, classically from eating undercooked infected pork products. Another common CNS parasite is Toxoplasma gondii
; Although widely prevalent in the population, it generally causes no symptoms but can cause active infection in patients with decreased immunity. Infrequently, other species of worms, such as Strongyloides
, can also cause meningitis.
Infectious encephalitis, a more severe infection, can caused by bacterial, viral, fungal, or parasitic infections and will commonly present with focal neurologic symptoms, behavioral change, cognitive deficits, or even seizures.3
The most common causes of meningoencephalitis are summarized in Table 18.1
Intracranial abscesses are distinct from the granulomas that form secondary to parasitic and TB infections and most often occur in those with immune disorders or recent surgery. Rarely, they can occur in healthy individuals with normal immune systems. Infections are most commonly caused by Streptococcus
species, followed by Staphylococcus
(predominantly S aureus
) and gram-negative bacteria (Proteus, E coli,
etc.). Mortality rate, although still relatively high, has declined to as low as 10% in recent years, likely secondary to advanced diagnostic and treatment modalities.4
The epidural space represents another site where CNS abscesses can occur. Unlike many of the other types of CNS infections discussed in this chapter, the incidence of epidural abscess has been increasing in recent years, likely caused by an increase in spinal procedures, increasing numbers of immunocompromised patients, and high numbers of intravenous (IV) drug users. S aureus is the most common pathogen involved in epidural abscesses, with a high proportion of methicillin-resistant S aureus (MRSA). Although rare, mycobacteria and fungi also can cause spinal epidural abscesses.
Finally, prions represent an unusual form of CNS infection. They are transmissible misfolded proteins that, once acquired, induce progressive, fatal CNS disease. They induce a group
of disorders known as transmissible spongiform encephalopathies (TSEs). TSEs are very rare, but include Kuru, Creutzfeldt-Jakob disease (CJD), and fatal familial insomnia (FFI), with CJD being the most common.9
TABLE 18.1 Common Etiologies of Meningoencephalitis in Adults
L monocytogenes (older individuals)
CMV, cytomegalovirus; EBV, Epstein-Barr virus; HIV, human immunodeficiency virus; HSV, herpes simplex virus; VZV, varicella-zoster virus.
The focus for prehospital providers is on recognizing critical patients and transporting them to the closest appropriate hospital. Given that many CNS pathologies can result in altered mental status and loss of protective airway mechanisms, an assessment of the patient’s airway and ability to oxygenate should be completed first following local emergency medical service (EMS) protocols. If there is a concern for bacterial meningitis (eg, a febrile patient with a headache and altered mental status), the patient and crew should maintain droplet precautions by using personal protective equipment to prevent the spread of the disease. If possible, IV access should be obtained and crystalloid fluid resuscitation started.
If seizures occur prior to arrival at the emergency department (ED), abortive therapy with intramuscular (IM) midazolam or lorazepam, or IV lorazepam is recommended. There is no evidence supporting the use of prehospital antibiotics; sepsis studies on prehospital antibiotics have not demonstrated improved mortality, and we currently do not recommend prehospital antibiotic treatment. If bacterial meningitis from meningococcus is confirmed, providers in close contact with the patient’s respiratory secretions (eg, the provider who intubated) should receive antibiotic prophylaxis (see discussion below and Table 18.2