Chapter 44: Meningitis/Encephalitis

DEFINITIONS

Meningitis: Inflammation of the meninges, the membranes covering the brain and spinal cord

Encephalitis: Inflammation of the brain parenchyma

ETIOLOGY

NEONATES <2 MONTHS

• Bacteria:

  • Group B Streptococcus (52%)

  • Escherichia coli and other gram-negative bacilli (rods) (27%)

  • Listeria monocytogenes (6%)

  • Anaerobes (3%)

  • Other gram-positive organisms (7%): enterococci, Streptococcus pneumoniae, staphylococci

  • Other gram-negative organisms (5%): Haemophilus influenzae, Neisseria meningitides, Pseudomonas

• Viruses: Herpes simplex virus (HSV), human herpesvirus 6 (HHV-6), enteroviruses, arboviruses, human immunodeficiency virus (HIV), adenovirus, varicella zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), measles, mumps, rubella, influenza, parainfluenza, parvovirus B19, rotavirus, others

INFANTS >2 MONTHS AND CHILDREN

• Bacteria:

  • S. pneumoniae and N. meningitidis (90%–95%)

  • Other organisms: H. influenzae, Salmonella species, group B Streptococcus, L. monocytogenes, anaerobes

• Viruses: Enteroviruses, arboviruses, HSV, HHV-6, HIV, adenovirus, VZV, EBV, CMV, measles, mumps, rubella, influenza, parainfluenza, parvovirus B19, rotavirus, zoonotic diseases, arthropod-borne diseases, others

SPECIAL POPULATIONS

• Mycoplasma tuberculosis: Consider based on history of exposure

• Fungi: Immunocompromised patients

• Parasites and protozoa: Consider based on history of exposure

• Rabies: Consider based on history of exposure

Enteroviruses account for 85% to 95% of viral meningoencephalitis in which an etiologic agent is identified.

CLINICAL MANIFESTATIONS

NEONATES/INFANTS

• Fever of unknown origin

• Vomiting, poor feeding, failure to thrive (FTT)

• Apnea or respiratory distress

• Altered mental status: irritability or lethargy

• Signs of increased intracranial pressure (ICP): bulging fontanelle

• Focal neurologic deficits

• Seizures

• Petechiae/purpura or rash

• Shock

OLDER CHILDREN

• Fever: almost always present

• Nausea/vomiting

• Headache, photophobia

• Back pain

• Altered mental status

• Focal neurologic deficits

• Seizures

• Signs of increased ICP: papilledema (if present, look for brain abscess, venous sinus thrombosis, and subdural fluid collection/empyema)

• Signs of meningeal irritation: positive Kernig's and Brudinski's signs

• Petechiae/purpura or rash

• Shock

DIAGNOSIS

LABORATORY EVALUATION

• Serum tests: abnormal white blood cell (WBC) count (leukocytosis or leukopenia), prominence of atypical lymphocytes (EBV), viral studies

• Cerebrospinal fluid (CSF) studies: cell count, WBC differential, glucose, protein, Gram stain, culture, viral studies (enterovirus polymerase chain reaction [PCR], HSV PCR, etc.), acid-fast bacillus AFB stain, tuberculosis culture – See Table 44-1

• Blood culture: positive in 80% to 90% of patients with suspected bacterial meningitis who were not pretreated with antibiotics

• Nasopharyngeal swab: For viral studies