eMedicine Specialties > Emergency Medicine > Pediatric

Pediatrics, Meningitis and Encephalitis: Differential Diagnoses & Workup

Author: Jeffrey Hom, MD, MPH, FACEP, Assistant Professor; Department of Pediatrics/Emergency Services and Department of Emergency Medicine; New York University School of Medicine
Coauthor(s): Robert Allan Felter, MD, FAAP, CPE, FACPE, Professor of Clinical Pediatrics, Department of Pediatrics, Georgetown University College of Medicine; Medical Director, Pediatric Emergency Medicine and Inpatient Services, Inova Loudoun Hospital, Leesburg, Virginia
Contributor Information and Disclosures

Updated: Nov 12, 2009

Differential Diagnoses

Pediatrics, Bacteremia and Sepsis
Pediatrics, Mumps
Pediatrics, Crying Child
Pediatrics, Reye Syndrome
Pediatrics, Febrile Seizures
Pediatrics, Headache
Pediatrics, Measles

Other Problems to Be Considered

Children who have partially treated meningitis or develop it while on antibiotics have modified signs and symptoms, and the diagnosis is usually delayed.

Workup

Laboratory Studies

  • Complete blood count (CBC) with differential
  • Blood cultures
  • Coagulation studies
  • Serum glucose
  • Electrolytes
  • Bacterial antigen studies can be performed on urine and serum; they can be useful in cases of pretreated meningitis. However, a negative bacterial antigen study result does not rule out meningitis.

Imaging Studies

  • Imaging studies rarely are required in the initial management of meningitis or encephalitis when the clinical presentation is typical. Exceptions include the need to rule out other pathology before performing an LP or when focal neurologic signs are present.
  • Imaging may be useful to check for abscesses, subdural effusions, empyema, or hydrocephalus.
  • Normal CT scan findings do not rule out increased intracranial pressure (ICP).

Other Tests

  • Preliminary studies have suggested procalcitonin to be a useful biomarker to the presence of bacterial meningitis. One study suggests that its use will enhance a sensitivity of a clinical decision rule, Bacterial Meningitis Score by Nigrovic et al.8,9,10

Procedures

  • The most important laboratory study is examination of CSF. The lumbar puncture (LP) should include opening and closing pressure in the cooperative patient.
    • Cell count
    • Gram stain
    • Culture and sensitivity
    • Glucose
    • Protein and antigen
    • Acid-fast bacillus
    • Fungal stains
  • Bacterial meningitis
    • White blood cell (WBC) counts over 1000/mm3 usually are caused by bacterial infections. Counts of 500-1000/mm3 may be bacterial or viral and need further evaluation. Lower counts are usually associated with viral infections. The total WBC count cannot definitely distinguish between bacterial and other causes. It was generally believed that a predominance of polymorphonucleocytes (PMNs) pointed to bacterial meningitis, but this has been unreliable. To differentiate bacterial and aseptic meningitis on the basis of percentage and absolute number of premature neutrophils (ie, bands) has been nondiagnostic.11
    • Gram stain may aid in diagnosis, but the diagnosis may be missed in up to 30-40% of cases of culture-proven disease. The sensitivity of a positive Gram stain is 67%.12
    • The protein concentration usually is elevated in bacterial meningitis, but it also is elevated by a traumatic tap. The glucose is usually reduced in bacterial meningitis. Normal CSF glucose should be greater than two-thirds that of the serum glucose. Levels less than 50% of serum are suggestive of bacterial meningitis.
    • Ancillary tests, such as total protein concentration, glucose concentration, and percent of neutrophils in CSF, are not helpful to for diagnosis, when the cell counts are low (less than 30/mm3). Its utility is useful only when they are highly abnormal.
    • Latex agglutination tests are available to test for S pneumoniae, H influenzae, group B Streptococcus, and N meningitidis. A negative result, however, does not rule out bacterial infection.
    • Even with normal CSF results, the fluid should be sent for culture. N meningitidis and S pneumoniae are known to give normal CSF results.
    • In cases where antibiotic administration leads to CSF sterilization, polymerase chain reaction (PCR) may have a role in identifying the pathogen. PCR is able to identify the pathogen quickly and accurately. The sample does not need to have a high number of organisms. However, this test needs further validation.
  • Clinical decision rule
    • There is an interest to differentiate bacterial meningitis and aseptic meningitis. To date, 5 clinical decision rules exist. These clinical decision rules identify low-risk patients by scoring or modeling clinical variables, blood variable, and CSF variables. With any clinical decision rule, they are used to identify patients at risk of meningitis. Those who are at low risk can avoid parenteral antibiotic and hospitalization.
    • The clinical decision rule by Nigrovic et al10 has shown high accuracy and simplicity of use. Comparison among the 5 clinical decision rules has not been performed. In addition, general applicability of these rules has not been validated.
  • Viral meningitis
    • The WBC count in viral meningitis is usually below 500/mm3, with greater than 50% lymphocytes.
    • The protein may be elevated.
    • The glucose level may be normal or low.
    • Gram stain results are negative.
  • Encephalitis
    • In addition to the studies for meningitis, an EEG, CT scan, and MRI have been used for evaluation.
    • More recently, PCR has been used for diagnosis.
    • CSF analysis shows pleocytosis (predominantly mononuclear cells) and high levels of protein. A small percentage (3-5%) of samples have normal CSF. Identification of viral antigen or nucleic acid may provide some diagnostic help.
    • Serial antibody analysis is helpful for prognostic purposes. Routine measurements do not aid in the treatment during the acute phase. New ELISA and PCR assays are available for diagnosis.
    • In cases of West Nile virus, CSF shows pleocytosis and moderately elevated protein levels. CT shows no abnormalities. MRI may show enhancement of meninges and periventricular regions. Diagnosis test is WNV ELISA. However, this test has cross reactivities to other flaviviruses.
  • Traumatic LP
    • If bleeding occurs during the procedure and the CSF is contaminated with blood, the interpretation becomes more difficult.
    • The use of corrected WBC:RBC ratio (1:500) and percent of neutrophils to "normalize" the cell count was shown to have limited utility in predicting those with meningitis. The "corrected CSF" was shown to underestimate the true white blood cell count, causing clinicians to underdiagnosis borderline meningitis cases.
    • In any situation when a traumatic LP occurs and the interpretation is difficult, it is better to treat and wait for the results of the CSF culture.
    • In very bloody LPs, a drop of the fluid on the sterile dressing usually will produce a double ring if there is CSF fluid present.
    • When in doubt, treat and attempt the LP later.

More on Pediatrics, Meningitis and Encephalitis

Overview: Pediatrics, Meningitis and Encephalitis
Differential Diagnoses & Workup: Pediatrics, Meningitis and Encephalitis
Treatment & Medication: Pediatrics, Meningitis and Encephalitis
Follow-up: Pediatrics, Meningitis and Encephalitis
References
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Further Reading

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Keywords

meningitis, meningitis symptoms, encephalitis symptoms, meningitis treatment, encephalitis treatment, encephalitis, meningitis in children, encephalitis in children, bacterial meningitis in children, viral meningitis in children, group B streptococci, group B streptococcal infection,

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Contributor Information and Disclosures

Author

Jeffrey Hom, MD, MPH, FACEP, Assistant Professor; Department of Pediatrics/Emergency Services and Department of Emergency Medicine; New York University School of Medicine
Jeffrey Hom, MD, MPH, FACEP is a member of the following medical societies: American Academy of Pediatrics, American College of Emergency Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Coauthor(s)

Robert Allan Felter, MD, FAAP, CPE, FACPE, Professor of Clinical Pediatrics, Department of Pediatrics, Georgetown University College of Medicine; Medical Director, Pediatric Emergency Medicine and Inpatient Services, Inova Loudoun Hospital, Leesburg, Virginia
Robert Allan Felter, MD, FAAP, CPE, FACPE is a member of the following medical societies: American Academy of Pediatrics and American College of Physician Executives
Disclosure: Nothing to disclose.

Medical Editor

Garry Wilkes, MBBS, FACEM, Director of Emergency Medicine, Bunbury Hospital, Western Australia; Medical Director, St John Ambulance, WA Ambulance Service; Adjunct Associate Professor, Edith Cowan University; Clinical Associate Professor, Rural Clinical School, University of Western Australia, Australia.
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from financial planner; Avanir Pharma Stock Investment from financial planner ; WebMD Salary and stock Employment and investment from financial planner

Managing Editor

Grace M Young, MD, Associate Professor, Department of Pediatrics, University of Maryland Medical Center
Grace M Young, MD is a member of the following medical societies: American Academy of Pediatrics and American College of Emergency Physicians
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Richard G Bachur, MD, Associate Professor of Pediatrics, Harvard Medical School; Associate Chief and Fellowship Director, Attending Physician, Division of Emergency Medicine, Children's Hospital of Boston
Richard G Bachur, MD is a member of the following medical societies: American Academy of Pediatrics, Society for Academic Emergency Medicine, and Society for Pediatric Research
Disclosure: Nothing to disclose.

 
 
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