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Meningitis and Encephalitis
A guide for patients and carers
Tests used to diagnose meningitis and encaphilitis
CT scan
A CT (computerised tomography) brain scan is a special type of x-ray which gives clear pictures of the brain. Occasionally a dye is injected into a vein in the arm which will help show any area of breakdown of the blood-brain barrier at the site of encephalitis or abscess. In addition the dye will sometimes also highlight inflammation of the meninges.
MRI scan
An MRI scan is a scanning procedure which gives even clearer pictures of the brain than a CT scan. The pictures are made by changes in a strong magnetic field rather than x-rays. MRI scanning is more likely to show any breakdown in the blood-brain barrier at an earlier stage than a CT scan. Again a dye (or contrast agent) may be used to give more information. The scan is painless but takes longer than a CT scan and the quality of the pictures can be affected by movement. The machine makes quite a loud knocking sound while it is in operation.
The following points are important:
• A brain scan is unnecessary in uncomplicated meningitis.
• A CT scan early in encephalitis does not usually show anything abnormal.
• An MRI scan early in encephalitis does not usually find anything abnormal or shows subtle changes in the temporal lobes in herpes simplex encephalitis.
• CT or MRI brain scanning is crucial if either a cerebral abscess or a stroke are suspected.
Lumbar puncture
The brain and spinal cord are surrounded by clear fluid called cerebrospinal fluid (CSF). To collect a sample of this fluid, a small injection of local anaesthetic is given to numb a patch of skin over the lower end of the spine (the lumbar area) and a needle is passed between two vertebrae (spinal bones) into the space containing the CSF. The CSF pressure can be measured and CSF can be taken and sent for tests.
In meningitis the CSF will appear cloudy rather than crystal clear. CSF in viral encephalitis may be normal or show changed levels of some components. The laboratory can usually have the results of these tests in a few hours. Other specialised tests for bacteria and viruses may take a few days.
Electroencephalogram (EEG)
An electroencephalogram involves having wires attached to the scalp, and then over a period of 20-30 minutes, a recording of the electrical activity of the brain is taken. The test is painless and safe. It is a useful procedure since it can show if the activity over the temporal lobes is abnormal - suggesting herpes simplex encephalitis - or show whether epilepsy is arising from a specific part of the brain.
OTHER TESTS
White blood cell count
Because bacterial meningitis is commonly found with septicaemia, there will often be an increase in the number of white blood cells in the blood.
Blood culture and sensitivity
The blood can be cultured in the laboratory and sometimes the bacteria or fungi causing the infection can be grown and identified.
Throat swab for culture and sensitivity
Bacteria can sometimes be grown from a swab of a throat infection and identified.
Stool culture for viruses or bacteria
Viruses or bacteria can sometimes be grown from a sample of faeces.
Urine culture and sensitivity for bacteria (especially used for suspected TB meningitis)
Bacteria from a urine sample can sometimes be grown and identified.
Chest x-ray
A chest x-ray may show pneumonia or changes which suggest TB.
Sputum culture and sensitivity
If there is a bacterial chest infection (or pneumonia) bacteria from saliva and mucus can sometimes be grown and identified.
A CT (computerised tomography) brain scan is a special type of x-ray which gives clear pictures of the brain. Occasionally a dye is injected into a vein in the arm which will help show any area of breakdown of the blood-brain barrier at the site of encephalitis or abscess. In addition the dye will sometimes also highlight inflammation of the meninges.
MRI scan
An MRI scan is a scanning procedure which gives even clearer pictures of the brain than a CT scan. The pictures are made by changes in a strong magnetic field rather than x-rays. MRI scanning is more likely to show any breakdown in the blood-brain barrier at an earlier stage than a CT scan. Again a dye (or contrast agent) may be used to give more information. The scan is painless but takes longer than a CT scan and the quality of the pictures can be affected by movement. The machine makes quite a loud knocking sound while it is in operation.
The following points are important:
• A brain scan is unnecessary in uncomplicated meningitis.
• A CT scan early in encephalitis does not usually show anything abnormal.
• An MRI scan early in encephalitis does not usually find anything abnormal or shows subtle changes in the temporal lobes in herpes simplex encephalitis.
• CT or MRI brain scanning is crucial if either a cerebral abscess or a stroke are suspected.
Lumbar puncture
The brain and spinal cord are surrounded by clear fluid called cerebrospinal fluid (CSF). To collect a sample of this fluid, a small injection of local anaesthetic is given to numb a patch of skin over the lower end of the spine (the lumbar area) and a needle is passed between two vertebrae (spinal bones) into the space containing the CSF. The CSF pressure can be measured and CSF can be taken and sent for tests.
In meningitis the CSF will appear cloudy rather than crystal clear. CSF in viral encephalitis may be normal or show changed levels of some components. The laboratory can usually have the results of these tests in a few hours. Other specialised tests for bacteria and viruses may take a few days.
Electroencephalogram (EEG)
An electroencephalogram involves having wires attached to the scalp, and then over a period of 20-30 minutes, a recording of the electrical activity of the brain is taken. The test is painless and safe. It is a useful procedure since it can show if the activity over the temporal lobes is abnormal - suggesting herpes simplex encephalitis - or show whether epilepsy is arising from a specific part of the brain.
OTHER TESTS
White blood cell count
Because bacterial meningitis is commonly found with septicaemia, there will often be an increase in the number of white blood cells in the blood.
Blood culture and sensitivity
The blood can be cultured in the laboratory and sometimes the bacteria or fungi causing the infection can be grown and identified.
Throat swab for culture and sensitivity
Bacteria can sometimes be grown from a swab of a throat infection and identified.
Stool culture for viruses or bacteria
Viruses or bacteria can sometimes be grown from a sample of faeces.
Urine culture and sensitivity for bacteria (especially used for suspected TB meningitis)
Bacteria from a urine sample can sometimes be grown and identified.
Chest x-ray
A chest x-ray may show pneumonia or changes which suggest TB.
Sputum culture and sensitivity
If there is a bacterial chest infection (or pneumonia) bacteria from saliva and mucus can sometimes be grown and identified.
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Page 5 of 15
Contents
- Introduction
- What is meningitis?
- What is encephalitis?
- What are the symptoms?
- Tests used to diagnose meningitis and encaphilitis
- Other problems that can be confused with meningitis and encaphilitis
- Treatment of meningitis
- Treatment of encaphalitis
- How well do people respond to treatment?
- Other help available to patients and carers
- Getting back to normal
- Things to be avoided
- Some do's and don'ts
- Summary
- Other Organisations that may be able to help
