In this article, we are talking about meningitis disease. For meningitis, meninges refers to the meninges which are three protective membranes that cover the brain and spinal cord and refers to inflammation; therefore meningitis is an inflammation of the meninges. More specifically, it refers to the inflammation of the two inner layers called leptomeningen.
The outermost layer of the meninges is the dura mater,
the middle layer is the parent arachnid and the innermost layer is the pia
mater. The latter two, the arachnids and the pious mother, are the leptomens.
Among the leptomena is the subarachnoid space, which houses the cerebrospinal
fluid, or cerebrospinal fluid.
Cerebrospinal fluid is a clear, watery fluid that is
pumped around the spinal cord and brain to protect them from shock and bathe
them in nutrients. In a microliter or cubic millimeter there are normally few
white blood cells, up to 5. If we observe a larger sample, say a deciliter,
about 70% of them will be made up of lymphocytes, 30% of monocytes and only a
few polymorphonuclear cells - PMN - like neutrophils. That same volume will
also contain some protein, around 15-50 mg, as well as some glucose, around
45-100 mg, which is nearly two-thirds of the glucose we would find in the same
blood volume. The CSF is kept under slight pressure, less than 200 mm H20, or
just under 15 mm of mercury - less than one fifth of average arterial pressure.
Now there are about 150ml of CSF in the body at any given time. This is
constantly being replenished, with around 500ml of new CSF being produced each
day and the excess, i.e. 500 minus 150ml or 350ml, being absorbed into the
blood. But for nutrients to move in and out of the CSF, and the brain itself,
they must cross the tightly regulated blood-brain barrier.
The blood-brain barrier is the special designation for
blood vessels in the brain. This is because the endothelial cells in the blood
vessels are so tightly bound together that they prevent them from leaking out
and only allow certain molecules to pass through.
Meningitis is inflammation of the leptomeningenes,
which are remembered as the two innermost membranes that surround the brain and
spinal cord. It is not the inflammation of the brain itself that is the
encephalitis; but sometimes they can occur together and when they do it is
called meningoencephalitis. So meningitis needs some kind of trigger for
inflammation and it can be an autoimmune disease, in which the body sticks,
such as lupus, or the body has a side effect on a drug, which can occur with
intrathecal therapy. , when the drug is taken directly injected into the
cerebrospinal fluid. But infection is by far the most common cause of
meningitis in all age groups, such as with the bacterium Neisseria meningitides
or the herpes simplex virus.
Ways To Spread Infection
Now, an infection takes two routes to reach the
cerebrospinal fluid and the leptomeninges.
Direct Broadcast
The first way is direct propagation, i. H when a
pathogen enters the skull or spine, then enters the meninges and finally ends
up in the cerebrospinal fluid. Sometimes the pathogen has passed through the
overlying skin or through the nose, but an anatomical defect is more likely to
be to blame. For example, it can be a congenital defect, such as spina bifida,
or an acquired defect, such as a fractured skull, which can cause CSF to leak
through the sinuses.
Hematogenous Spread
The second route is hematogenous spread, in which a
pathogen enters the bloodstream and travels through endothelial cells into the
blood vessels that make up the blood-brain barrier and into the CSF. To do
this, pathogens typically must bind to surface receptors on endothelial cells
in order to pass through. Otherwise, they must find damaged or more vulnerable
areas such as the choroid plexus. As soon as the pathogen has found its way
into the alcohol, it can multiply. Before long, the handful of white blood
cells monitoring the CSF identify the pathogen and release cytokines to recruit
additional immune cells. Over time, one microliter of CSF can contain up to
thousands of white blood cells, but more than five usually defines meningitis.
In most bacterial cases there are more than 100 white
blood cells per microliter and more than 90% of PMN. In most viral cases, there
are 10 to 1000 white blood cells; more than 50% of lymphocytes and less than
20% of PMN. In most cases of fungi there are 10-500 white blood cells, with
more than 50% of lymphocytes.
In most cases of tuberculous meningitis, there are
50-500 white blood cells, more than 80% of which are lymphocytes. The extra immune
cells draw more moisture to the area and start causing local destruction as
they try to control the infection. Consequently, cerebrospinal fluid pressure
generally exceeds 200 mm H2O. The immune response causes the concentration of
glucose in the cerebrospinal fluid to drop below two-thirds of the
concentration in the blood and increases the protein content to over 50 mg per
deciliter.
Causes
When it comes to the causes of meningitis, viruses and bacteria mainly cause acute meningitis, while fungi mainly cause chronic meningitis. There are now many options for bacteria. In newborns, the most common causes are group B streptococci, E. coli and Listeria monocytogenes. In children and adolescents, the most common causes are Neisseria meningitidis and Streptococcus pneumonia. In adults and the elderly, the most common causes are Streptococcus pneumonia and Listeria monocytogenes.
There are also tick-borne causes of meningitis, such
as the bacteria Borrelia burgdorferi, which causes Lyme disease. When it comes
to viruses, the main culprits are enteroviruses, especially Coxsackie virus and
herpes simplex virus. HIV is usually transmitted through bodily fluids and can
also cause viral meningitis. Less common causes are mumps virus, varicella
zoster virus, and lymphocytic choriomeningitis virus.
There are also fungi, such as those of the genera
Cryptococcus and Coccidioides, which mainly affect immunocompromised people.
And then of course there are tuberculous meningitis caused by the bacterium
Mycobacterium tuberculosis and finally the parasitic causes of meningitis such
as P. falciparum which is the main cause of malaria.
Symptoms
Well, the classic triad of symptoms for meningitis is a headache, fever, and a stiff or stiff neck. It can also cause photophobia, which is discomfort with bright lights, or phonophobia, discomfort with loud noises. Meningoencephalitis can lead to altered mental status or seizures.
Diagnosis
The diagnosis of meningitis begins with a physical examination. A maneuver occurs when a person lies on their back facing up and one of their legs is lifted with the knee bent at a 90 degree angle. Then the leg is supported and slowly extended at the knee. When this causes back pain, it is called Kernig's sign.
Another maneuver is to lie on your back, face up,
supporting and arching your neck. If this causes the knees or hips to bend
automatically, it is called Brudzinski's sign.
If meningitis is suspected, a lumbar puncture may be
done. This is when a needle passes through the lower lumbar vertebral levels of
the spinal cord, for example, between L3 and L4. The needle enters the
subarachnoid space and a few milliliters of cerebrospinal fluid are collected.
Opening pressure can be measured and CSF can be analyzed for white blood cells,
proteins and glucose.
Polymerase chain reaction, or PCR, can be used to find
specific causes such as HIV, enterovirus, HSV, or tuberculosis. If a particular
infection appears to be an obvious cause, a test such as the Western blot for
Borrelia burgdorferi bacteria or a thin blood smear for malaria can be used.
Treatment
Treatment of meningitis depends on the underlying cause.
Bacterial Meningitis:
For bacterial meningitis, it is common practice to administer steroids and then
antibiotics, to prevent extensive damage to the leptomeninges from inflammation
caused by the antibiotics that destroy the bacteria.
Medicines:
In general, treatment - antiviral, antibacterial, antifungal or antiparasitic
is targeted at the specific cause of meningitis.
Vaccine: Prevention with
a vaccine is indicated for some causes such as Neisseria meningitidis, but also
for mumps and metastatic tuberculosis.
Antibiotics:
Prophylactic antibiotics can also be given to prevent outbreaks of bacterial
meningitis, such as in families where people have not been vaccinated against
Neisseria meningitis.
Conclusion
Meningitis is inflammation of the leptomeninges, the
two innermost membranes that surround and protect both the brain and spinal
cord. It normally begins when a foreign substance, often bacteria, makes its
way into the leptomen, either by direct contact or by blood diffusion across
the blood brain barrier. The immune system responds to the antigen by flooding
the subarachnoid space with white blood cells, which release chemokines - and
cause inflammation, resulting in the classic triad of symptoms: headache,
fever, and neck stiffness.
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