Meningitis and Encephalitis What s the Difference

							Title:
Meningitis and Encephalitis: What's
the Difference?

Word Count:
905

Summary:
Meningitis and encephalitis are ser
ious infections of the nervous syst
em requiring prompt medical evaluat
ion. However, they are not the same
 thing, and distinguishing between
the two conditions can be crucial.


Keywords:
meningitis,encephalitis,virus,viral
,bacteria,bacterial,infection,CSF,c
erebrospinal fluid,lumbar puncture,
spinal tap


Article Body:
"Meningitis" and "encephalitis" are
 two words that pop onto most peopl
e's radar screens from time to time
, and usually in some scary context
, like hearing of a cluster of case
s in their child's school, or readi
ng media reports of epidemics occur
ring nationally or internationally.
 While most people understand that
these words mean there is some sort
 of infection of the nervous system
, other distinctions and implicatio
ns are often left unstated and, as
a result, can be vague or confusing.

The basic concepts are built into t
he words themselves. Starting at th
e ends of the words and working for
wards, "-itis" is the medical suffi
x meaning inflammation. Although it
's possible for inflammation to occ
ur without an infection being prese
nt, as a practical matter, in most
cases of meningitis or encephalitis
 the inflammation is indeed due to
an infection.

The next step in understanding thes
e concepts is to analyze the first
parts of the words. "Mening-" refer
s to the meninges which are the mem
branous coverings of the brain and
spinal cord. So "meningitis" means
inflammation or infection of these
membranous coverings. By contrast,
"encephal-" refers to the encephalo
n or brain (originating from the Gr
eek word "enkephalos"), so "encepha
litis" means inflammation or infect
ion of the brain itself.

Although no case of meningitis or e
ncephalitis is trivial, depending o
n the particulars, some cases end u
p as temporary illnesses from which
 there is full recovery, while othe
rs can be severely damaging or even
 lethal. In a nutshell, cases of me
ningitis caused by viruses are usua
lly associated with good outcomes (
even without treatment), while case
s of meningitis involving bacteria
are very serious and require emerge
ncy treatment with powerful antibio
tics. All cases of encephalitis--us
ually caused by viruses and not by
bacteria--are serious, and antivira
l treatment is available for some o
f the viruses involved, but not all.

Most cases of either meningitis or
encephalitis start fairly abruptly,
 sometimes following an obvious inf
ection elsewhere in the body and so
metimes not. As with most infection
s, a fever is usually present in me
ningitis or encephalitis, but is no
t necessarily striking. In both cas
es the patient feels miserable in g
eneral and often complains of pain
in the head, neck, or both.

Because encephalitis involves infec
tion of the brain itself, symptoms
of altered brain function--like con
fusion or decreased alertness--are
usually present, while in cases of
meningitis the patient is initially
 alert and, though understandably d
istracted by pain and misery, still
 in command of their mental process
es.

In either case, prompt medical asse
ssment is important. In both mening
itis and encephalitis a lumbar punc
ture (also known as a spinal tap) i
s usually crucial in detecting the
presence of an infection, identifyi
ng the infecting organism, and guid
ing successful treatment. While an
imaging test like a CT scan or an M
RI scan is often included as part o
f the evaluation, they do not repla
ce the lumbar puncture in identifyi
ng the essential features of the in
fection.

A lumbar puncture is usually perfor
med with the patient lying on one s
ide, curled into a fetal position.
The doctor preps and drapes the pat
ient's lower back to create a steri
le field in which to work. After nu
mbing the skin of the lower back th
e doctor inserts a needle in the mi
ddle of the spine, puncturing the m
eninges. In the lower back there is
 no spinal cord, so there is no ris
k of puncturing it, too. Watery flu
id is collected into tubes as it dr
ips out of the back of the needle.
Then the needle is withdrawn.

This watery fluid is called CSF--sh
ort for cerebrospinal fluid--and be
cause it resides within the meninge
s (and outside of the brain and spi
nal cord) it holds some of the keys
 to diagnosing the infection. Labor
atory personnel can perform several
 tests on the fluid right away, lik
e measuring the concentrations of r
ed and white blood cells, as well a
s the concentrations of protein and
 sugar. An increase in concentratio
n of white blood ("pus") cells and
an increase in protein concentratio
n are expected findings when the me
ninges are infected by either bacte
ria or viruses, with the changes mo
re pronounced in bacterial infectio
ns than in viral infections. Reduct
ions in sugar concentration are com
mon in bacterial but not viral infe
ctions. Other tests on the CSF invo
lve inherent delays, like trying to
 grow bacteria from the CSF in Petr
i dishes or other culture media.

In truth, cases of encephalitis als
o usually involve inflammation of t
he meninges, so a stickler for ling
uistic accuracy could rightly maint
ain that they should be called "men
ingo-encephalitis" to reflect the i
nvolvements of both meninges and br
ain. But in common usage, the "meni
ngo-" prefix is often dropped. So b
ecause CSF changes occur in cases o
f both meningitis and encephalitis,
 the main clinical feature that sep
arates the two is the patient's men
tal state, with confusion or decrea
sed level of consciousness making a
 strong case for encephalitis.

Once the CSF has been collected, th
e doctor can begin treatment withou
t risk of obscuring the fluid's dia
gnostic features. So long as there
is any likelihood of bacterial infe
ction, the doctor administers one o
r more antibiotic drugs, usually vi
a an intravenous catheter. If the c
linical findings could also be inte
rpreted as due to a treatable virus
, the doctor concurrently administe
rs an antiviral drug. With the seri
ousness of these illnesses, the ben
efits of over-treatment exceed its
risks, and once the dust settles an
d the diagnosis is clarified, needl
ess treatment can be discontinued w
ithout harm.

(C) 2005 by Gary Cordingley