By Dr Ananya Mandal, MD
Meningitis is inflammation of the meninges and can be diagnosed using laboratory and imaging studies.
Ruling out other conditions
There are several clinical signs and symptoms that may raise the suspicion of meningitis. However, before diagnosing meningitis other conditions that have similar clinical presentation need to be ruled out. These include:
- fever for other infections
- abscess within the brain
- other causes of confusion and altered mental state like brain infection (encephalitis), bleeding within the brain or stroke (subarachnoid haemorrhage), brain tumors etc.
Whatever may be the cause, symptoms of meningitis should be dealt with as a priority and on an emergency basis since the course of the disease may turn rapidly life threatening and fatal.
Investigations suggested for diagnosis of meningitis include lumbar puncture, complete blood count and so forth.
This is performed immediately providing there are no signs of raised intracranial pressure. This includes bad headache, raised fontanelle among babies, seizures, loss of consciousness etc.)
Samples of cerebrospinal fluid taken from the lumbar puncture are sent to the laboratory for staining with special dyes that reveal the organism leading to meningitis.
The common stains and tests used are:
- Gram stain (to diagnose gram negative Meningococci, E. coli, Pseudomona and gram positive staphylococci and Pneumococci)
- Ziehl-Neelsen stain (for diagnosing tuberculosis)
- cytology (for abnormal cells)
- virology (for causative viruses)
- glucose, protein, culture (to check for growth of specific bacteria)
- rapid antigen screen or polymerase chain reaction (PCR) if available
- India ink for Cryptococci (fungal infection)
During early stages the CSF may be normal.
Other methods used to diagnose meningitis
- Complete blood count to detect anemia and infection (by raised WBC counts)
- Blood culture for diagnosing infection and septicaemia
- Blood glucose to compare it with CSF glucose
- Renal and liver function tests
- Tests to check adequate blood clotting ability
- Chest X ray to detect lung pathologies like lung abscess, tuberculosis etc.
- Urine culture to detect organisms
- Nasal swab and stool for virology if viral meningitis is suspected
- Whole blood real-time PCR testing (EDTA sample) for N. meningitidis to confirm a diagnosis of meningococcal disease
- CT scan or computed tomography scan and MRI scan (Magnetic resonance imaging scan) to check for brain tumors, abscesses and other pathologies.
- Blood antigen tests for Cryptococcus and India ink and CSF cryptococcal antigen
- Blood tests for syphilis if syphilis involvement of meninges is suspected.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)
Last Updated: Oct 14, 2012