C h a p t e r 3 7
Disorders of Brain Function
941
by nausea, vomiting, photophobia, and altered mental
status.
42,44
Other signs include seizures, cranial nerve
palsies, and focal cerebral signs. Meningococcal menin-
gitis is characterized by a petechial (petite hemorrhagic
spots) rash with palpable purpura (bleeding into the
skin) in most people. These petechiae vary in size from
pinhead to large ecchymoses or even areas of skin gan-
grene, often associated with rapid onset of hypotension,
acute adrenal hemorrhage (Waterhouse-Friderichsen
syndrome), and multiple organ failure. Persons infected
with
H. influenzae
or
S. pneumoniae
may present with
difficulty in arousal and seizures, whereas those with
N. meningitidis
infection may present with delirium or
coma. Cranial nerve damage (especially CN VIII, with
resulting deafness) and hydrocephalus may occur as
complications of pyogenic meningitis.
Diagnosis of bacterial meningitis is based on the his-
tory and physical examination, along with laboratory
data. A stiff neck is an early sign of meningeal irritation.
Moving the neck forward, either actively or passively, is
difficult. Two assessment techniques can help determine
whether meningeal irritation is present.
7
The
Kernig sign
is resistance to extension of the knee while the person is
lying with the hip flexed at a right angle. The
Brudzinski
sign
is elicited when flexion of the neck induces flexion
of the hip and knee. These postures reflect resistance to
the painful stretching of the inflamed meninges from
the lumbar level to the head. Lumbar puncture find-
ings, which are necessary for accurate diagnosis, include
a cloudy and purulent CSF under increased pressure.
Bacteria can be seen on smears and can easily be cul-
tured with appropriate media. Occasionally, previous
antibiotic use limits culture sensitivities, in which case
latex agglutination or polymerase chain reaction (PCR)
testing for
N. meningitidis, H. influenzae,
and
Listeria
species can be used. Because complications associated
with lumbar puncture include life-threatening cerebral
herniation, at-risk patients (i.e., those who are immu-
nocompromised, had a seizure within a week, have
papilledema, or have specific neurologic abnormalities)
should have a CT scan before undergoing the procedure.
Treatment includes urgent administration of antimi-
crobial therapy while diagnostic testing ensues. Delay
in initiation of antimicrobial therapy, most frequently
because of performance of medical imaging before per-
formance of lumbar puncture or transfer to another med-
ical facility, can result in poor outcomes.
43,44
Because of
the emergence of penicillin- and cephalosporin-resistant
strains of
S. pneumoniae
, a combination of antimi-
crobial agents is usually used. Effective antimicrobial
treatment produces rapid lysis of the pathogen, which
produces inflammatory mediators that have the poten-
tial for exacerbating the abnormalities of the blood–
brain barrier. To suppress this pathologic inflammation,
adjunctive corticosteroid therapy is increasingly admin-
istered with or just before the first dose of antibiotics in
patients of all ages.
43,44
Persons who have been exposed to someone with menin
gococcal meningitis should be treated prophylactically
with antibiotics. A quadrivalent polysaccharide–protein
conjugate vaccine is now available to protect against
meningococcal meningitis. The vaccine is recommended
for adolescents aged 11 to 18 years, first-year college
students living in dormitories, military recruits, and
microbiologists with occupational exposure. The vac-
cine is also recommended for persons aged
≥
9 months
who travel to or reside in regions in which meningo-
coccal disease is endemic and for all persons aged
≥
2 months with conditions such as complement com-
ponent deficiencies or anatomic or functional asplenia.
The vaccine dosing schedule varies by age at time of
previous vaccination.
45
Viral Meningitis
Viral meningitis can be caused by many different viruses,
most often enteroviruses, including coxsackievirus,
poliovirus, and echovirus. Others include Epstein-Barr
virus, mumps virus, herpes simplex virus (HSV), and
West Nile virus. Often the virus cannot be identified.
Viral meningitis manifests in much the same way as
bacterial meningitis, but the course is less severe and
the CSF findings are markedly different. There are lym-
phocytes in the CSF rather than polymorphonuclear
cells, the protein content is only moderately elevated,
and the sugar content usually is normal. The acute viral
meningitides are self-limited and usually require only
symptomatic treatment, except for herpes simplex virus
(HSV) type 2, which responds to intravenous acyclovir.
Encephalitis
Encephalitis represents a generalized infection of the
parenchyma of the brain or spinal cord.
1,4,7,46
It usually
is caused by a virus, but it also may be caused by bac-
teria, fungi, and other organisms. The nervous system
is subject to invasion by many viruses, such as arbo-
virus, poliovirus, and rabies virus. The mode of trans-
mission may be the bite of a mosquito (arbovirus), a
rabid animal (rabies virus), or ingestion (poliovirus).
Common causes of encephalitis in the United States are
herpes simplex virus (HSV) and West Nile virus. Less-
frequent causes of encephalitis are toxic substances such
as ingested lead and vaccines for measles and mumps.
Encephalitis caused by human immunodeficiency virus
(HIV) infection is discussed in Chapter 16.
The pathologic picture of encephalitis includes local
necrotizing hemorrhage, which ultimately becomes gen-
eralized, with prominent edema. There is progressive
degeneration of nerve cell bodies. The histologic picture,
although rather general, may demonstrate some specific
characteristics. For example, the poliovirus selectively
destroys the cells of the anterior horn of the spinal cord.
Like meningitis, encephalitis is characterized by fever,
headache, and nuchal rigidity, but more often patients
also experience neurologic disturbances, such as leth-
argy, disorientation, seizures, focal paralysis, delirium,
and coma. Diagnosis of encephalitis is made by clinical
history and presenting symptoms, in addition to tradi-
tional CSF studies.
