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Meningitis is an inflammation of the leptomeninges (arachnoid and pia mater). It is a medical emergency requiring rapid diagnosis and early treatment. Infectious meningitis is a devastating process with a high morbidity and mortality.

Etiology
The causes are divided into infectious and aseptic, the second group are those patients in whom the spinal fluid has a high lymphocyte count (> 50%), a moderate increase in protein, normal glucose, Gram stain and negative microbiological study .
There are several diseases (bacterial endocarditis) and conditions (splenectomy, sickle cell disease) that predispose a picture of meningitis. The pneumococcus is the most common etiologic agent in adults, followed in order of importance the meningococcus, H. influenzae, Listeria monocytogenes and with the advent of AIDS, Cryptococcus.

Pathogenesis
Infectious agents enter the meninges in several ways:
1. Hematogenously during bacteremia
2. Since infections of upper respiratory tract (skull fractures, birth defects of the dura)
3. Through the skull, nasopharyngeal venules
4. By direct spread of an underlying infectious focus (sinusitis, intraventricular rupture of brain abscess)
5. By introduction of organisms during surgical or diagnostic procedures (lumbar puncture). Once the meningeal infection, it spreads rapidly through the subarachnoid space.

Neurologic findings

The cranial nerve dysfunction primarily affects the third, fourth, sixth and seventh cranial nerves, appears in 10-20% of bacterial meningitis. Hemiparesis, dysphasia and hemianopsia, occurring in 15% of patients with pyogenic meningitis. The persistence of cerebral localizing signs suggestive of cerebral arteritis, thrombophlebitis of cortical veins or space occupying lesions such as brain abscess. Bacterial meningitis causes acute cerebral edema that can produce seizures, hypotension, bradycardia and coma. In elderly patients, infants or meningeal signs may not be present.

Eruption. The appearance of a purpuric rash or maculopetequial in a patient with meningitis, the etiologic diagnosis geared toward miningocócica infection but may be confused with cutaneous aseptic meningitis by echovirus type 9.

Diagnostic Aid

Suspicion of meningitis should be a lumbar puncture and cerebrospinal fluid study. Three basic patterns can be found in CSF:

1. Purulent
2. Lymphocytes with normal glucose levels
3. Lymphoma with low levels of glucose

The pattern has lots of purulent polymorphonuclear decreased glucose levels and elevation in protein. The most common cause is bacterial meningitis. The pattern has lymphoma with normal glucose as the main causes of viral meningitis or meningitis and malignant lymphoma with impaired glucose pattern, meanwhile, is the result of tuberculous or fungal meningitis.

The cell count in the CSF of most bacterial meningitis varies between 100 to 5,000 cells per mm3 of which 80% are neutrophils.

The culture and Gram stain of centrifuged CSF are essential and are often positive in 70% of patients who have not received previous antibiotics.

When Gram stain is negative it is recommended that latex agglutination test with specific antigens for pneumococcus, meningococcus and Cryptococcus neoformans particularly useful in partially treated cases.

Also practiced stain and culture for mycobacteria, India ink examination and evaluation for fresh mushrooms to find both. Blood culture is irrelevant, because in 40 to 80% of patients, depending on the germ, usually a positive result.

In cases of aseptic meningitis should be performed VDRL in blood and cerebrospinal fluid. It is advisable, if warranted table, chest radiographs, sinus and mastoid and brain computed tomography.

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