For brain infections, see Brain Infections, for neonatal meningitis, see Infections in Neonates: Neonatal Bacterial Meningitis )
Meningitis is inflammation of the meninges of the brain or spinal cord.
Meningitis is often infectious and is one of the most common CNS infections. Inflammation involves both the meninges and brain parenchyma (meningoencephalitis). Meningitis may become evident over hours or days (acute) or a longer period (subacute or chronic).
The most common types of acute meningitis are
Acute bacterial meningitis
Acute bacterial meningitis is a severe illness characterized by purulent CSF. It is rapidly progressive and, without treatment, fatal.
Aseptic meningitis is milder and typically self-limited; it is usually caused by viruses.
Symptoms and Signs
Many cases of infectious meningitis begin with a vague prodrome of viral symptoms. The classic meningitis triad of fever, headache, and nuchal rigidity develops over hours or days. Passive flexion of the neck is restricted and painful, but rotation and extension are typically not as painful. In severe cases, attempts at neck flexion may induce flexion of the hip or knee (Brudzinski’s sign), and there may be resistance to passive extension of the knee while the hip is flexed (Kernig’s sign). Neck stiffness and Brudzinski’s and Kernig’s signs are termed meningeal signs or meningismus; they occur because tension on nerve roots passing through inflamed meninges causes irritation.
Although brain parenchyma is not typically involved early in meningitis, lethargy, confusion, seizures, and focal deficits will develop if bacterial meningitis is left untreated.
Blood DNA PCR for bacterial pathogens
Sometimes CT before lumbar puncture
Acute meningitis is a medical emergency that requires rapid diagnosis and treatment. After IV access is secured, blood samples are drawn for culture, CBC, and PCR of bacterial pathogens if available. Treatment is started empirically.
Lumbar puncture is done to obtain CSF for Gram stain, culture, cell count and differential, glucose concentration, protein content and other specialized tests. These tests must be done in a timely manner. However, patients with signs compatible with a mass lesion (eg, focal deficits, papilledema, deterioration in consciousness, seizures) require head CT before lumbar puncture because there is a small possibility that lumbar puncture can cause cerebral herniation if a brain abscess or other mass lesion is present.
CSF findings aid in the diagnosis of meningitis (see Table 1: Meningitis: Cerebrospinal Fluid Abnormalities in Various Infections). Presence of bacteria on Gram stain or growth of bacteria in culture is diagnostic of bacterial meningitis. Gram stain is positive about 80% of the time in bacterial meningitis and usually differentiates among the common causative pathogens. CSF lymphocytosis and absence of pathogens suggest aseptic meningitis but may represent partially treated bacterial meningitis.
Cerebrospinal Fluid Abnormalities in Various Infections
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If patients appear ill and have findings of meningitis, antibiotics (see Meningitis: Antibiotics) are started as soon as blood cultures are drawn. If patients do not appear very ill and the diagnosis is less certain, antibiotics can await CSF results.