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| {{Meningitis}}
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| {{CMG}}; '''Associate Editor(s)-In-Chief:''' {{CZ}}
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| ==Overview==
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| ==Laboratory Evaluations==
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| Investigations include [[blood test]]s (electrolytes, liver and kidney function, inflammatory markers and a [[complete blood count]]) and usually [[X-ray]] examination of the chest. The most important test in identifying or ruling out meningitis is analysis of the [[cerebrospinal fluid]] (fluid that envelops the brain and the spinal cord) through [[lumbar puncture]] (LP). However, if the patient is at risk for a cerebral mass lesion or elevated [[intracranial pressure]] (recent head injury, a known immune system problem, localizing neurological signs, or evidence on examination of a raised ICP), a lumbar puncture may be contraindicated because of the possibility of fatal [[brain herniation]]. In such cases a [[Computed tomography|CT]] or [[Magnetic resonance imaging|MRI]] scan is generally performed prior to the lumbar puncture to exclude this possibility. Otherwise, the CT or MRI should be performed after the LP, with MRI preferred over CT due to its superiority in demonstrating areas of cerebral edema, ischemia, and meningeal inflammation.
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| During the lumbar puncture procedure, the opening pressure is measured. A pressure of over 180 mmH<sub>2</sub>O is indicative of bacterial meningitis.
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| The CSF sample is examined for [[white blood cell]]s (and which subtypes), [[red blood cell]]s, [[protein]] content and [[glucose]] level. [[Gram staining]] of the sample may demonstrate bacteria in bacterial meningitis, but absence of bacteria does not exclude bacterial meningitis; [[microbiological culture]] of the sample may still yield a causative organism. The type of white blood cell predominantly present predicts whether meningitis is due to bacterial or [[virus|viral]] infection. Other tests performed on the CSF sample include [[latex agglutination test]], limulus lysates, or [[polymerase chain reaction]] (PCR) for bacterial or viral DNA. If the patient is [[immunodeficiency|immunocompromised]], testing the CSF for [[toxoplasmosis]], [[Epstein-Barr virus]], [[cytomegalovirus]], [[JC virus]] and [[fungi|fungal infection]] may be performed.
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| [[Image:Streptococcus pneumoniae meningitis, gross pathology 33 lores.jpg|thumb|200px|right|An [[autopsy]] demonstrating signs of [[pneumococcus|pneumococcal]] '''meningitis'''. The [[forceps]] (center) are retracting the [[dura mater]] (white). Underneath the dura mater are the [[leptomeninges]], which are [[edema]]tous and have multiple small [[hemorrhage|hemorrhagic]] foci (red).]]
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| {| style="background:#FDF5E6;padding:0.3em; margin-left:5px; border:1px solid #996666"
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| |+ style="color:#996666"|'''CSF finding in different conditions'''<ref>{{cite book |last=Provan |first= Drew|authorlink= |coauthors=Andrew Krentz |title= Oxford Handbook of clinical and laboratory investigation|year=2005 |publisher=Oxford university press |location=Oxford |isbn=0198566638 }}</ref>
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| !bgcolor="#FFEFD5"|Condition !! bgcolor="#FFEFD5"|Glucose !! bgcolor="#FFEFD5"|Protein!!bgcolor="#FFEFD5"|Cells
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| |-
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| ! bgcolor="#FFEFD5"|Acute bacterial meningitis
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| | Low|| high||high, often > 300/mm³
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| |-
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| ! bgcolor="#FFEFD5"|Acute viral meningitis
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| |Normal ||normal or high|| [[Lymphocyte|mononuclear]], < 300/mm³
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| |-
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| ! bgcolor="#FFEFD5"|Tuberculous meningitis
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| |Low ||high||[[pleocytosis]], mixed < 300/mm³
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| |-
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| ! bgcolor="#FFEFD5"|Fungal meningitis
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| |Low||high||< 300/mm³
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| |-
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| ! bgcolor="#FFEFD5"|Malignant meningitis
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| |Low ||high||usually mononuclear
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| |-
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| ! bgcolor="#FFEFD5"|Subarachnoid haemorrhage
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| |Normal ||normal, or high ||[[Erythrocytes]]
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| |}
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| {|
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| |-style="background:silver; color:black"
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| | '''Cerebrospinal Fluid''' || || || || ||
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| |-style="background:silver; color:black"
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| | || '''Normal Levels''' || '''Acute Bacterial M.''' || '''Acute Viral M.''' || '''TB M.''' || '''Neuroborreliosis'''
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| |- style="background:silver; color:black"
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| | '''Cells/ul''' || '''< 5''' || '''In the 1000s''' || '''In the 100s''' || '''In the 100s''' || '''Some 100'''
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| |-style="background:silver; color:black"
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| | '''Cells''' || '''Lymph:Monos 7:3''' || '''Gran. > Lymph.''' || '''Lymph. > Gran.''' || '''Various leukos''' || '''Lymph. monocytic'''
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| |-style="background:silver; color:black"
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| | '''Total Protein (mg/dl)''' || '''45-60''' || '''Typically 100-500''' || '''Typically normal''' || '''Typically 100-200''' || '''Typically up to 350'''
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| |-style="background:silver; color:black"
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| | '''Glucose Ratio (CSF/plasma)''' || '''Typically > 0.5''' || '''< 0.3''' || '''> 0.6''' || '''< 0.5''' || '''Normal'''
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| |-style="background:silver; color:black"
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| | '''Lactate (mmol/l)''' || '''< 2.1''' || '''> 2.1''' || '''< 2.1''' || '''> 2.1''' || '''-'''
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| |-style="background:silver; color:black"
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| | '''Others''' || '''ICP: 6-22 (cm H2O)''' || || '''PCR of HSV-DNA''' || '''PCR of TBC-DNA''' || '''IgG/IgM <br> CSF/Serum Ratio'''
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| |}
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| <br clear="left"/>
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| In bacterial meningitis, the CSF glucose to serum glucose ratio is < 0.4. The Gram stain is positive in >60% of cases, and culture in >80%. Latex agglutination may be positive in meningitis due to ''[[Streptococcus pneumoniae]]'', ''[[Neisseria meningitidis]]'', ''[[Haemophilus influenzae]]'', ''[[Escherichia coli]]'', Group B Streptococci. Limulus lysates may be positive in Gram-negative meningitis.
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| ==CSF Cultures==
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| Cultures are often negative if CSF is taken after the administration of antibiotics. In these patients, [[polymerase chain reaction|PCR]] can be helpful in arriving at a diagnosis. It has been suggested that CSF [[cortisol]] measurement may be helpful.<ref>{{cite journal | title=Cortisol levels in cerebrospinal fluid correlate with severity and bacterial origin of meningitis | author=Holub M, Beran O, Dzupova O, ''et al.'' | journal=Critical Care | year=2007 | volume=11 | pages=R41 | doi=10.1186/cc5729 }}</ref>
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| ==Prediction rules==
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| The Bacterial Meningitis Score predicts reliably whether a child (older than two months) may have infectious meningitis. In children with at least 1 risk factor (positive CSF Gram stain, CSF absolute neutrophil count ≥ 1000 cell/µL, CSF protein ≥ 80 mg/dL, peripheral blood absolute neutrophil count ≥ 10,000 cell/µL, history of seizure before or at presentation time) it had a [[sensitivity (tests)|sensitivity]] of 100%, [[specificity (tests)|specificity]] of 63.5%, and negative predictive value of 100%.<ref>{{cite journal |author=Nigrovic LE, Kuppermann N, Macias CG, ''et al'' |title=Clinical prediction rule for identifying children with cerebrospinal fluid pleocytosis at very low risk of bacterial meningitis |journal=JAMA |volume=297 |issue=1 |pages=52-60 |year=2007 |pmid=17200475 |doi=10.1001/jama.297.1.52}}</ref>
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| ==References==
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| {{reflist|2}}
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| [[Category:Disease]]
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| [[Category:Infectious disease]]
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| [[Category:Neurology]]
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| [[Category:Emergency medicine]]
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