Many pathogens of all classes—bacterial, viral, parasitic, and fungal—can affect the nervous system, both centrally and peripherally. The risks and short- and long-term outcomes from exposure to a pathogen vary significantly depending on a patient’s age, with a fetus and an adolescent having very different responses to the same pathogen. This chapter begins with a brief introduction to different types of neurologic infections and then briefly covers the most common infectious pathogens in each pediatric age range (fetal, neonatal, and infant/childhood/adolescent). We then briefly discuss neurologic infections unique and common in the developing world, in immunocompromised children, and in children with neurologic hardware.
TYPES OF NERVOUS SYSTEM INFECTIONS
There are several mechanisms for pathogens to cause nervous system injury. Meningitis is defined as direct invasion and inflammation of the meninges itself. Common meningitis symptoms in children include fever, headache, nuchal rigidity (in those with a closed anterior fontanelle), vomiting, seizures, cranial neuropathies, and altered mental status. Brudzinski and Kernig signs are both used during neurologic exams to look for signs of meningitis but are not sensitive in those with an open anterior fontanelle.
Encephalitis, in contrast, is inflammation of the brain itself. Clinical symptoms of encephalitis are similar to meningitis, but typically, the altered mental status is more severe. Other neurologic symptoms, such as seizures, ataxia, and focal deficits, may occur. Meningitis and encephalitis often co-occur, and patients are referred to as having meningoencephalitis when symptoms of both are present.
At times, focal infections in the nervous system can become encapsulated, causing a purulent abscess, most commonly in fungal and bacterial infections, or an enclosed cyst, as in neurocysticercosis. This can be seen after localized extension of infections from elsewhere (eg, sinusitis, ear infections, mastoiditis, dental infections). If the collection is in the subdural space, it is classified as a subdural empyema. Ventriculitis denotes significant involvement of the ventricles, most commonly in bacterial meningitis, which may cause hydrocephalus.
Even when there is no direct invasion of the central or peripheral nervous systems, some infections can have postinflammatory effects that lead to neurologic diseases, such as acute disseminated encephalomyelitis (ADEM), Bell’s Palsy, focal cerebral arteriopathy and vasculitis, Guillain-Barré syndrome, plexitis, or Sydenham chorea.
FETAL INFECTIONS OF THE NERVOUS SYSTEM
Fetal life is one of the most dangerous times for the central nervous system (CNS) to be exposed to an infection, as the fetus’s CNS is undergoing critical periods of neurodevelopment for the entire duration of pregnancy. Infections that cause minimal or no nervous system injury in postnatal life, such as rubella and cytomegalovirus (CMV), may be devastating during fetal development. The most common fetal infections are frequently remembered by the mnemonics TORCH (toxoplasmosis, other, rubella, CMV, and herpes simplex) and SCRATCHES (syphilis, CMV, rubella, AIDS, toxoplasmosis, chickenpox/varicella, herpes simplex, and Enterovirus) (Table 34–1)....