+ CSF findings in different forms of<unk>  Type of<unk>  Glucose Protein Cells Acute bacterial low high PMNs, often > 300/mm³ Acute viral normal normal or high mononuclear, PMNs, mononuclear Diagnosing<unk>  as promptly as possible can improve outcomes. There is no specific sign or symptom that can diagnose<unk>  and a lumbar puncture (spinal tap) to examine the cerebrospinal fluid is recommended for diagnosis. Lumbar puncture is contraindicated if there is a mass in the brain (tumor or abscess) or the intracranial pressure (ICP) is elevated, as it may lead to brain herniation. If someone is at risk for either a mass or raised ICP (recent head injury, a known immune system problem, localizing neurological signs, or evidence on examination of a raised ICP), a CT or MRI scan is recommended prior to the lumbar puncture. This applies in 45% of all adult cases. There are no physical tests that can rule out or determine if a person has<unk> . The jolt accentuation test is not specific or sensitive enough to completely rule out<unk> . If someone is suspected of having<unk> , blood tests are performed for markers of inflammation (e.g. C-reactive protein, complete blood count), as well as blood cultures. If a CT or MRI is required before LP, or if LP proves difficult, professional guidelines suggest that antibiotics should be administered first to prevent delay in treatment, especially if this may be longer than 30 minutes. Often, CT or MRI scans are performed at a later stage to assess for complications of<unk> . In severe forms of<unk> , monitoring of blood electrolytes may be important; for example, hyponatremia is common in bacterial<unk> . The cause of hyponatremia, however, is controversial and may include dehydration, the inappropriate secretion of the antidiuretic hormone (SIADH), or overly aggressive intravenous fluid administration. Lumbar puncture Cloudy CSF from a person with<unk>  due to Streptococcus Gram stain of meningococci from a culture showing Gram negative (pink) bacteria, often in pairs A lumbar puncture is done by positioning the person, usually lying on the side, applying local anesthetic, and inserting a needle into the dural sac (a sac around the spinal cord) to collect cerebrospinal fluid (CSF). When this has been achieved, the "opening pressure" of the CSF is measured using a manometer. The pressure is normally between 6 and 18 cm water (cmH2O); in bacterial<unk>  the pressure is usually elevated. In cryptococcal<unk> , intracranial pressure is markedly elevated. The initial appearance of the fluid may prove an indication of the nature of the infection: cloudy CSF indicates higher levels of protein, white and red blood cells and/or bacteria, and therefore may suggest bacterial<unk> . The CSF sample is examined for presence and types of white blood cells, red blood cells, protein content and glucose level. Gram staining of the sample may demonstrate bacteria in bacterial<unk> , but absence of bacteria does not exclude bacterial<unk>  as they are only seen in 60% of cases; this figure is reduced by a further 20% if antibiotics were administered before the sample was taken. Gram staining is also less reliable in particular infections such as listeriosis. Microbiological culture of the sample is more sensitive (it identifies the organism in 70–85% of cases) but results can take up to 48 hours to become available. The type of white blood cell predominantly present (see table) indicates whether<unk>  is bacterial (usually neutrophil-predominant) or viral (usually lymphocyte-predominant), although at the beginning of the disease this is not always a reliable indicator. Less commonly, eosinophils predominate, suggesting parasitic or fungal etiology, among others. The concentration of glucose in CSF is normally above 40% of that in blood. In bacterial<unk>  it is typically lower; the CSF glucose level is therefore divided by the blood glucose (CSF glucose to serum glucose ratio). A ratio ≤0.4 is indicative of bacterial<unk> ; in the newborn, glucose levels in CSF are normally higher, and a ratio below 0.6 (60%) is therefore considered abnormal. High levels of lactate in CSF indicate a higher likelihood of bacterial<unk> , as does a higher white blood cell count. If lactate levels are less than 35 mg/dl and the person has not previously received antibiotics then this may rule out bacterial<unk> . Various other specialized tests may be used to distinguish between different types of<unk> . A latex agglutination test may be positive in<unk>  caused by Streptococcus pneumoniae, Neisseria<unk> is, Haemophilus influenzae, Escherichia coli and group B streptococci; its routine use is not encouraged as it rarely leads to changes in treatment, but it may be used if other tests are not diagnostic. Similarly, the limulus lysate test may be positive in<unk>  caused by Gram-negative bacteria, but it is of limited use unless other tests have been unhelpful. Polymerase chain reaction (PCR) is a technique used to amplify small traces of bacterial DNA in order to detect the presence of bacterial or viral DNA in cerebrospinal fluid; it is a highly sensitive and specific test since only trace amounts of the infecting agent's DNA is required. It may identify bacteria in bacterial<unk>  and may assist in distinguishing the various causes of viral<unk>  (enterovirus, herpes simplex virus 2 and mumps in those not vaccinated for this). Serology (identification of antibodies to viruses) may be useful in viral<unk> . If tuberculous<unk>  is suspected, the sample is processed for Ziehl–Neelsen stain, which has a low sensitivity, and tuberculosis culture, which takes a long time to process; PCR is being used increasingly. Diagnosis of cryptococcal<unk>  can be made at low cost using an India ink stain of the CSF; however, testing for cryptococcal antigen in blood or CSF is more sensitive. A diagnostic and therapeutic difficulty is "partially treated<unk> ", where there are<unk>  symptoms after receiving antibiotics (such as for presumptive sinusitis). When this happens, CSF findings may resemble those of viral<unk> , but antibiotic treatment may need to be continued until there is definitive positive evidence of a viral cause (e.g. a positive enterovirus PCR). Postmortem Histopathology of bacterial<unk> : autopsy case of a person with pneumococcal<unk>  showing inflammatory infiltrates of the pia mater consisting of neutrophil granulocytes (inset, higher magnification).<unk>  can be diagnosed after death has occurred. The findings from a post mortem are usually a widespread inflammation of the pia mater and arachnoid layers of the meninges. Neutrophil granulocytes tend to have migrated to the cerebrospinal fluid and the base of the brain, along with cranial nerves and the spinal cord, may be surrounded with pus – as may the meningeal vessels.
Meningitis
Lyme disease
Cerebritis
Naegleriasis
Encephalitis
Meningoencephalitis
Neuroleptic malignant syndrome
Meninges