LABORATORY DIAGNOSIS OF MENINGITISM. HARINI PRIYADHARSHINIII MBBS

ACUTE INFECTIONS OF NERVOUS SYSTEM

• These are among the most important problems in medicine today

• Common acute infections of the nervous system include:Acute bacterial meningitisViral meningitisBrain abscessEmpyema Encephalitis

• Each may present with a non-specific prodrome of fever and headache.

MENINGITIS• Inflammatory process of leptomeninges and CSF

within the subarachnoid space.• Meningoencephalitis combines this with

inflammation of brain parenchyma.• Meningitis is usually caused by a infection - Acute pyogenic(bacterial)or aseptic (viral) and Chronic(usually due to tuberculous, spirochetal or cryptococcal).

MENINGITIS

ACUTE BACTERIAL• Acute purulent

infection within the subarachnoid space.

• Associated with CNS inflammatory reactions that may result in decreased consciousness, seizures, raised ICP etc

VIRAL• Usually present with

headache, fever and signs of meningeal irritation coupled with inflammatory CSF.

• The headache of viral meningitis is often frontal or retro-orbital associated with photophobia and pain on eye movement.

LAB DIAGNOSIS • CSF EXAMINATION• HISTOPATHOLOGY• LATEX AGGLUTNATION• POLYMERASE CHAIN REACTION• VIRAL CULTURE• RAPID DIAGNOSTICTESTS (RDT)• SEROLOGIC STUDIES• OTHER LAB STUDIES

CYTOLOGIC STUDIES OF CSF

• Laboratory examination of the CSF is usually the first step to confirm the presence of meningitis.

• Cytological examination should precede centrifugation and heating of CSF.

CSF EXAMINATION• The typical profile:

CSF opening pressure: 50–180 mmH2OGlucose: 40–85 mg/dL.

Protein (total): 15–45 mg/dL.Leukocytes (WBC): 0–5/µL (adults / children);

up to 30/µL (newborns). Culture: sterile.

Gross appearance: Normal CSF is clear and colorless.

Differential: 60–70% lymphocytes; up to 30% monocytes 

    and macrophages; other cells 2% or less.

VIRAL MENINGITIS

• Glucose (mg/dL): Normal (> 40 mg/dL.)• Protein (mg/dL) <100 mg/dL (moderate

increase)• WBCs (cells/µL) < 100 cells/µL.• Cell differential: Early: neutrophils. Late:

lymphocytes.• Culture: Negative• Opening Pressure Usually normal

BACTERIAL MENINGITIS• Glucose (mg/dL): Normal to marked decrease.

<40 mg/dL.• Protein (mg/dL): (Marked increase) > 250 mg/dL.• WBCs (cells/µL): >500 (usually > 1000). Early: May

be < 100.• Cell differential: Predominance of Neutrophils

(PMNs)• Culture: Positive• Opening Pressure: Elevated

CSF COLLECTION : LUMBAR PUNCTURE

HISTOPATHOLOGY• Neutrophils fill the subarachnoid space in severely

affected areas and are found predominantly around the leptomeningeal blood vessels in the

less severe cases.

NEISSERIA MENINGITIDIS

STREPTOCOCCUS PNEUMONIAE

LATEX AGGLUTINATION• Positive reaction: agglutination (or visible clumping) of the

latex particles and slight clearing of the suspension occurs within 2-10 minutes .

• Negative reaction: the suspension remains homogenous and slightly milky in appearance.

POLYMERASE CHAIN REACTION• Amplification of virus specific DNA or RNA from

CSF using PCR amplification has become the single most effective method for diagnosing CSF viral infections.

• 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 meningitis and may assist in distinguishing the various causes of viral meningitis.

VIRAL CULTURE• The sensitivity of CSF cultures for the diagnosis of

viral meningitis is poor in comparison to the detection of bacterial meningitis.

• Viruses may also be isolated from throat swabs, blood and urine.

• Enterovirus and adenoviruses maybe found in the feces.

Proper streaking and growth of N. meningitidis on a Blood Agar Plate

Proper streaking and growth of S. pneumoniae on a Blood Agar Plate

Proper streaking and growth of H. influenzae on a Chocolate Agar Plate

SEROLOGIC STUDIES

• Crucial diagnostic tool• Serum antibody detection is less useful for

viruses with high prevalence rates in the general population.

• For viruses with low prevalence rates , diagnosis of acute viral infection can be made by documenting

• Seroconversion between acute phase and convalescent sera.

• The documentation of synthesis of virus specific antibodies in CSF is more useful than serum serology alone.

RAPID DIAGNOSTIC TESTS (RDT)• RDTs have been developed for direct testing of

CSF specimens without prior heat or centrifugation.

• The test is based on the principle of vertical flow immunochromatography.

• Gold particles and nitrocellulose membranes are coated with monoclonal antibodies to capture soluble serogroup-specific polysaccharide antigens in the CSF.

READING THE RDT RESULTS• Appearance of red lines on the dipsticks will

indicate whether one of the four meningococcal serogroups has been detected in the CSF.

• The upper line on the dipstick is the positive control and should always be present.

• If the CSF is positive for one of the serogroups, a lower red line will also be present. The position of that red line indicates the specific serogroup based on the RDT that was tested.

• A negative result consists of a single upper pink control line only.

OTHER LABORATORY STUDIES

• CBC (complete blood count) & DLC (differential leucocyte count)

• Liver and Renal function tests• ESR (erythrocyte sedimentation rate)• C- Reactive protein• Electrolytes etc• MRI and CT are not necessary in patients with

uncomplicated meningitis.• They may be performed in patients with altered

consciousness, seizures etc

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YOU