Meningitis is an infection of the coverings around the brain and spinal cord.
The infection occurs most often in children, teens, and young adults. Also at risk are older adults and people who have long-term health problems, such as a weakened immune system.
Why Diagnosing Meningitis is Important
Diagnosing Meningitis is top priority in clinical Medicine, in particular Bacterial meingitis, can be a life threatening condition , the need for appreciate antibiotic therapy at the earliest is a priority.
Minimal Diagnostic faculties if done with precision can reduce morbidity and mortality
On suspicion of Meningitis
Every patient suspected of having Meningitis should have a specimen of CSF examination in the laboratory to establish the infection and to rule out infection .
Basic Understanding on Meningitis
On a broad basis Meningitis is classified as
1 Purulent Meingitis
2 Aseptic Meingitis
What is Purulent Meningitis
The CSF appears typically turbid due to the presence of Leucocytes 100 to several thousands / mm 3 most of which are Polymorphonuclear leucocytes
Major Aetiological agents of Meningitis
3 Haemophilus influenzae
On majority of the occasions the pathogens pass from Respiratory tract via blood stream and infect Meningtis
Can occur at any age
Neonates and Infants Meningitis
There is specific affinity of some pathogens infecting Neonates and Infants
1 Coli forms
2 ß hemolytic streptococci
4 Salmonella and Listeria Monocytogenes
Carelessly performed Lumbar puncture
Accidental wound infection in neurosurgical wounds
Coli form bacilli
CSF infection in Venous shunts
When venous shunts are implanted for therapeutic purposes
or some other Saprophytic bacteria which rarely cause infection in normal people can infect meningis
In these conditions CSF is clear or only slightly turbid contain moderate number of leucocytes
10 – 500 / mm 3
Majority of cells are lymphocytes, except in early stages.
majority are caused by viruses
Aetiological agents of Aseptic Meningitis
Mumps virus moderately infective
Measles – Adenovirus
CSF resembles - Aseptic Meningitis
Few conditions associated with other etiological agent resemble aseptic meingitis
( Serovars Canicola icterohaemorrhagea )
Fungi ( Cryptococcus neofroms )
Amoeba – Naegleria, Harmanella.
Confusing CSF appereance
When early treatment is given in Bacterial meingitis the Clinico pathological apperance appears as Viral meingitis
In viral Encephalitis modereate Lympoyte exduate is found as it in Viral meingitis
On many occasions Tuberculosis present as Aseptic meingitis, results from Pulmonary or mesentric tuberculosis
Can be associated with Miliary tuberculosis.
Cell counts on CSF will reveal 100 – 500 leucocytes / mm 3
Majority are Lymphocytes
May form veil clot when CSF is allowed to stand in a undisturbed state.
Specimen collection for CSF Examination
Lumbar puncture to collect the CSF for examination to be collected by Physician trained in procedure with aseptic precautions to prevent introduction of Infection.
Procedure to collect CSF
The trained physician will collect only 3-5 ml into a labelled sterile container
Removal of large volume of CSF lead to headache,
The fluid to be collected at the rate of 4-5 drops per second.
If sudden removal of fluid is allowed may draw down cerebellum into the Foramen magnum and compress the Medulla of the Brain
CSF needs a New and Sterile container
Fresh sterile screw capped container to be used.
Reused containers not to be used contamination from the previous specimens misrepresent the present specimen .
Lumbar puncture for CSF collection
The best site for puncture is inter space between 3 and 4 lumbar vertebrae
( Corresponds to highest point of iliac crest )
The Physcian should wear sterile gloves and conduct the procedure with sterile precautions, The site of procedure should be disinfected and sterile occlusive dressing applied to the puncture site after the procedure.
Transportation to Laboratory
The collected specimen of CSF to be dispatched promptly to Laboratory , delay may cause death of delicate pathogens eg Meningococci and disintegrate leukocyte
Preservation of CSF
It is important when there is delay in transportation of specimens to Laboratory do not keep in Refrigerator, which tends to kill H.influenzae.
If delay is anticipated leave at Room Temperature.
A simultaneous blood culture should be collected in all suspected cases of Meningitis before the Antibiotics are started
Many cases of Bacterial ( Pyogenic )
meningitis are associated with Bacteriaemia
Septic spots in Meningtis
Patients having Meiningococcal Meningtis present with several septic spots.
The spots should be scraped and fluid examined for demonostration of Gram - ve cocci, on several occaions bacteria are not seen in CSF
Laboratory Examination of CSF
The specimens should be examined with naked eye
Look for Turbidity
Contamination with Blood
Normal CSF appears like water
CSF to be examined for
Estimation of protein and glucose
Cell counts in CSF
Microscopic examination of uncentrigured, well mixed CSF is done in slide counting chamber.
Count the number of
Normal cell counts
CSF normally contains 0- 5 leucocytes / mm 3
Newly born children contain upto 30/mm 3
In purulent Meningtis there are usually 100 – 300 leucocytes/mm3
In aseptic meningitis there are usually 10 – 500 leucocytes/mm 3
Mostly lymphocytes, though polymorphs may predominate in the earliest stage of the illness.
In Tuberculosis meingitis there are usually 100 – 500 leucocytes/mm 3
Care in Counting the Cells
When counting the cells, care must be taken to identify the RBC and rare presence of yeasts, amoeba should not be mistaken for leukocytes
Differential Leukocyte counts
If there is any difficulty in differentiating polymorphs and lymphocytes in the counting chamber
Make a film of cellular deposit after specimen has been centrifuged
leishman or Carol thionine and examined under oil immersion to asses the relative number of two types of leucocytes
Gram Staining of CSF
The CSF to be centrifuged to deposit the cells and bacteria
The film made from the deposit to be stained with Gram’s method
Make a thick smear with of area spread 10 mm in diameter encircle by a scratch on the surface of the slide
If the CSF appears turbid make a thin film
All the smears are dried and fixed on heat
Examination of Gram Stained smear
A careful search for Bacteria to be made in particular where there are plenty of leucocytes
At least keen observation to be done for 10 mt before reporting a negative smear.
Observe for the Presence of
One should be familiar with the following bacteria for successful reporting
Coli form bacilli
All the results are promptly reported to treating Physician
When variety of bacteria are found specimens may be contaminated.
May need a fresh specimen for examination
Culturing of CSF
The deposited sediment plated on culture media
incubated with 5-10%
A part of the specimen inoculated into Robertson's cooked medium
In suspected cases of Brain abscess Bacteriods and anaerobic cocci are cultured in anaerobic medium
Direct antibiotic sensitivity detection
When the organisms are numerous on Gram stained film CSF can be directly inoculated into Blood agar and Chocolate agar
The commonly used effective antibiotic disks are tested with sensitivity pattern,
Commonly we can test Benzyl Pencillin, and Choramphenicol
The antibiotic sensitivity pattern can be reported at the earliest
Dealing with Growth in Robertson's Cooked medium
If the turbidity devlops in RCM the broth should be filmed and subcultured on to Blood agar and Chocolate agar plates and incubated both aerobically and aerobically.
Biochemical testing for Infections
CSF should be tested for quantization of
Glucose and Protein
Normal CSF contain
2.2 to 4mmol/liter correlates to 60% of the plasma levels
Protein is present at concentration of 0.15 to 0.4 grams/liter
It can be higher in neonates can be upto 1.5 grams / liter
In pyogenic meningitis Protein concentration is increased and Glucose concentration decreased.
In aseptic meningitis Glucose concentration is normal and protein concentration raised
Tests for Bacterial antigen Detection
Co agglutination Tests
There are several test kits avialble commercially for detection antigens of
Diagnosis of Viral Meningitis
The virus are to be isolated from CSF
Presence of Viral antibodies by paired sampling of serum
In few viral infections the virus can be isolated from
Specimens of feces
Viruses - Meningitis
The following viruses can cause Aseptic meningitis
3 Herpes virus
Tuberculosis Meningitis -Diagnosis
CSF should be tested for presence of Acid fast bacilli by simple Ziehl Neelsen method
The deposit of the concentrate can be inoculated onto Lowenstein Jensens Medium
Other tests which support diagnosis are Reduction of Glucose, Protein is increased
Leptospiral Meningtis - Diagnosis
On few occasions in endemic areas Leptospira can produce meningitis
Rarely Leptospira can be seen in CSF under Dark ground microscopy
Cane cultured on Korthoff other Leptospiral medium
Antibiotic Selection in Meningitis
In the past Benzyl Pencillin or Choramphenicol are given in majority of cases suspected with meningitis.
In the recent past several new generation of Cephalosporins are replacing past theraputic ideas.
It is important to isolate and identify the causative agent.
However it is essential to start a theraputic trail with best clinical guess before the laboratory results are available.
Problems in Devloping World
It is much difficult to deal with precision in Devloping countries as many several infrastructural facilities are not available and Physicians have work their best of the previous clinical experiences.
The wisdom of treating Physicians still save several lives in the third world countries.
Created for benefit of Medical and paramedical Students in Devloping World Dr.T.V.Rao MD Email [email_address]