Approach Considerations

Laboratory examination of the cerebrospinal fluid (CSF) usually confirms the presence of meningitis.

In the US, a neuroimaging study (either MRI or CT scanning) prior to lumbar puncture is mandatory in all patients in whom meningitis is suspected. However, this rule is relaxed in several other countries (see CT scanning and MRI).

CSF Examination

Typical CSF abnormalities in meningitis include the following:

Increased opening pressure (>180 mm water)
Pleocytosis of polymorphonuclear leukocytes (white blood cell [WBC] counts between 10 and 10,000 cells/µL, predominantly neutrophils)
Decreased glucose concentration (< 45 mg/dL)
Increased protein concentration (>45 mg/dL)

Gram stain and culture of CSF identify the etiologic organism, N meningitides. In bacterial meningitis, Gram stain is positive in 70-90% of untreated cases, and culture results are positive in as many as 80% of cases.

More specialized laboratory tests, which may include culture of CSF and blood specimens, are needed for identification of N meningitidis and the serogroup of meningococci, as well as for determining its susceptibility to antibiotics.

Polymerase Chain Reaction

The polymerase chain reaction (PCR)^[12]may be used to complement standard laboratory procedures for the diagnosis of meningococcal meningitis.^[13]The IS1106 PCR is a rapid and sensitive test for confirmation of the diagnosis; its sensitivity is not affected by prior antibiotic treatment.^[14]PCR of the nspA gene was also reported to be a fast diagnostic test.^[15]

CT Scanning and MRI

Head CT scan findings are usually normal but may reveal signs of intracranial hypertension, edema, and intracerebral hemorrhage. In several parts of the world, imaging is an important cause of delay of therapy. In the US, due to the large availability of brain imaging, the performance of a head CT scan is mandatory. In other countries, this rule is relaxed, and indications for performing CT scanning prior to lumbar puncture include altered level of consciousness, papilledema, focal neurological deficits, and/or focal or generalized seizure activity.

The image below depicts intracerebral hemorrhage foci and diffuse edema in a patient with meningitis.

Head CT shows small intracerebral hemorrhage foci (vertical closed arrow). Basal ganglia can also not be visualized because of diffuse edema (oblique closed arrow). The black arrow head on the left shows soft tissue edema.

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MRI with contrast is preferred to CT scanning, because MRI better demonstrates meningeal lesions, cerebral edema, and cerebral ischemia. T1 may show obliterated cisterns. Contrast enhances the cisterns, and extension of enhancing subarachnoid exudate deep into the sulci may be seen in severe cases.

Strokes can be seen with the development of vasculitis and cerebritis. CNS complications that can be visualized with MRI include hydrocephalus, aqueductal obstruction, ventriculitis (especially in neonates), choroid plexitis, subdural effusion, and empyema.

Head CT demonstrates enlargement of the temporal horns indicating increased intracranial pressure (horizontal open large arrow). The closed arrowhead shows small intracerebral hemorrhage foci on the right temporal lobe, and the curved arrow shows the effect of increased intracranial pressure on the cerebellum.

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Histologic Findings

During the first few days, the subarachnoid and ventricular exudate contains large numbers of neutrophils and necrotic debris. Intracellular and extracellular bacteria can be demonstrated. The exudate extends along the perivascular spaces into the cortex and cerebral cortex. Purulent material usually is observed in the choroid plexus. With time, the number of mononuclear leukocytes increases, and they predominate by the end of the first week. Fibroblasts also proliferate.

Inflammatory cells infiltrate leptomeningeal and cortical arteries and veins and accumulate in the intima. Thrombosis of small vessels leads to infarction. This pattern is common in autopsied cases.

Other Tests

An electroencephalogram (EEG) study is sometimes useful to document irritable electrical patterns that may predispose the patient to seizures. Periodic complexes and periodic lateralizing epileptiform discharges (PLEDs) may be suggestive of encephalitis caused by herpes simplex virus.

Treatment & Management

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Media Gallery

Head CT demonstrates enlargement of the temporal horns indicating increased intracranial pressure (horizontal open large arrow). The closed arrowhead shows small intracerebral hemorrhage foci on the right temporal lobe, and the curved arrow shows the effect of increased intracranial pressure on the cerebellum.
Head CT shows small intracerebral hemorrhage foci (vertical closed arrow). Basal ganglia can also not be visualized because of diffuse edema (oblique closed arrow). The black arrow head on the left shows soft tissue edema.

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Author

Francisco de Assis Aquino Gondim, MD, PhD, MSc, FAAN Professor Adjunto of Neurology and Clinical Skills, Department of Internal Medicine, Universidade Federal do Ceará, Brazil

Francisco de Assis Aquino Gondim, MD, PhD, MSc, FAAN is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, International Parkinson and Movement Disorder Society

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Consultant for Pfizer, PTC Therapeutics and Alnylam<br/>Serve(d) as a speaker or a member of a speakers bureau for: Speaker for Shire, PTC Therapeutics and BSL Beringer<br/>Received travel grants from for: Aché, Biogen, Genzyme, Ipsen, Novartis, Baxter, Teva, Pfizer.

Coauthor(s)

Manish K Singh, MD Assistant Professor, Department of Neurology, Teaching Faculty for Pain Management and Neurology Residency Program, Hahnemann University Hospital, Drexel College of Medicine; Medical Director, Neurology and Pain Management, Jersey Institute of Neuroscience

Manish K Singh, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Pain Medicine, American Headache Society, American Association of Physicians of Indian Origin, American Medical Association, American Society of Regional Anesthesia and Pain Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Florian P Thomas, MD, PhD, MA, MS Chair, Neuroscience Institute and Department of Neurology, Director, Hereditary Neuropathy Center, Co-Director, Center for Memory Loss and Brain Health, Co-Director, ALS Center, Hackensack University Medical Center; Associate Dean of Faculty, Founding Chair and Professor, Department of Neurology, Hackensack Meridian School of Medicine

Florian P Thomas, MD, PhD, MA, MS is a member of the following medical societies: Academy of Spinal Cord Injury Professionals, American Academy of Neurology, American Neurological Association, Consortium of Multiple Sclerosis Centers, National Multiple Sclerosis Society, Sigma Xi, The Scientific Research Honor Society

Disclosure: Nothing to disclose.

Chief Editor

Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM Adjunct Associate Professor of Neurology, University of Missouri-Columbia School of Medicine; Medical Director of St Mary's Stroke Program, SSM Neurosciences Institute, SSM Health

Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, American Headache Society

Disclosure: Nothing to disclose.

Additional Contributors

Norman C Reynolds, Jr, MD Neurologist, Veterans Affairs Medical Center of Milwaukee; Clinical Professor, Medical College of Wisconsin

Norman C Reynolds, Jr, MD is a member of the following medical societies: American Academy of Neurology, Association of Military Surgeons of the US, International Parkinson and Movement Disorder Society, Sigma Xi, The Scientific Research Honor Society, Society for Neuroscience

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author Sidney E Croul, MD, to the development and writing of the source article.