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Encephalitis Differential Diagnoses

  • Author: David S Howes, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
 
Updated: Apr 13, 2016
 
 

Diagnostic Considerations

See the following for more information:

Other conditions to be considered include the following:

  • Acute central nervous system (CNS) events, such as hemorrhagic stroke
  • Acute confusional states secondary to drugs, toxins, psychosis
  • Amoeba (Naegleria, Acanthamoeba)
  • Head trauma
  • CNS syphilis
  • Ehrlichiosis
  • Intracranial hemorrhage
  • Intracranial tumor
  • CNS trauma

Differential Diagnoses

 
 
Contributor Information and Disclosures
Author

David S Howes, MD Professor of Medicine and Pediatrics, Residency Program Director Emeritus, Section of Emergency Medicine, University of Chicago, University of Chicago, The Pritzker School of Medicine

David S Howes, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Coauthor(s)

Marjorie Lazoff, MD Editor-in-Chief, Medical Computing Review

Marjorie Lazoff, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Informatics Association, American College of Emergency Physicians, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

Barry E Brenner, MD, PhD, FACEP Professor of Emergency Medicine, Professor of Internal Medicine, Program Director for Emergency Medicine, Case Medical Center, University Hospitals, Case Western Reserve University School of Medicine

Barry E Brenner, MD, PhD, FACEP is a member of the following medical societies: Alpha Omega Alpha, American Heart Association, American Thoracic Society, Arkansas Medical Society, New York Academy of Medicine, New York Academy of Sciences, Society for Academic Emergency Medicine, American Academy of Emergency Medicine, American College of Chest Physicians, American College of Emergency Physicians, American College of Physicians

Disclosure: Nothing to disclose.

Acknowledgements

Steven A Conrad, MD, PhD Chief, Department of Emergency Medicine; Chief, Multidisciplinary Critical Care Service, Professor, Department of Emergency and Internal Medicine, Louisiana State University Health Sciences Center

Steven A Conrad, MD, PhD is a member of the following medical societies: American College of Chest Physicians, American College of Critical Care Medicine, American College of Emergency Physicians, American College of Physicians, International Society for Heart and Lung Transplantation, Louisiana State Medical Society, Shock Society, Society for Academic Emergency Medicine, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Robin R Hemphill, MD, MPH Associate Professor, Director, Quality and Safety, Department of Emergency Medicine, Emory University School of Medicine

Robin R Hemphill, MD, MPH is a member of the following medical societies: American College of Emergency Physicians and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

J Stephen Huff, MD Associate Professor of Emergency Medicine and Neurology, Department of Emergency Medicine, University of Virginia School of Medicine

J Stephen Huff, MD is a member of the following medical societies: American Academy of Emergency Medicine, American Academy of Neurology, American College of Emergency Physicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Todd Pritz, MD Intensivist, St Anthony's Medical Center and St John's Mercy Medical Center

Todd Pritz, MD is a member of the following medical societies: Massachusetts Medical Society and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

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

Disclosure: Medscape Reference Salary Employment

References
  1. [Guideline] Tunkel AR, Glaser CA, Bloch KC, Sejvar JJ, Marra CM, Roos KL, et al. The management of encephalitis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2008 Aug 1. 47(3):303-27. [Medline].

  2. Final 2008 West Nile Virus Activity in the United States. Centers for Disease Control and Prevention. Available at http://bit.ly/fATcE1. Accessed: April 26, 2009.

  3. MacDonald RD, Krym VF. West Nile virus. Primer for family physicians. Can Fam Physician. 2005 Jun. 51:833-7. [Medline].

  4. Yao K, Honarmand S, Espinosa A, Akhyani N, Glaser C, Jacobson S. Detection of human herpesvirus-6 in cerebrospinal fluid of patients with encephalitis. Ann Neurol. 2009 Mar. 65(3):257-67. [Medline].

  5. Bloch KC, Glaser C. Diagnostic approaches for patients with suspected encephalitis. Curr Infect Dis Rep. 2007 Jul. 9(4):315-22. [Medline].

  6. Hayasaka D, Aoki K, Morita K. Development of simple and rapid assay to detect viral RNA of tick-borne encephalitis virus by reverse transcription-loop-mediated isothermal amplification. Virol J. 2013 Mar 4. 10(1):68. [Medline].

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Table. Cerebrospinal Fluid Findings by Type of Organism
CSF Finding (Normal)Bacterial MeningitisViral Meningitis*Fungal Meningitis
Pressure (5-15 cm water)
  • Increased
  • Normal or mildly increased
  • Normal or mildly increased in most fungal and tuberculous CNS infections
  • Patients with AIDS and cryptococcal meningitis are at increased risk of blindness and death unless pressure maintained at < 30 cm
Cell counts, mononuclear cells/µL



Preterm (0-25)



Term (0-22)



6 mo+ (0-5)



  • Normal cell count excludes bacterial meningitis
  • Typically thousands of polymorphonuclear cells, but counts may not change dramatically or even be normal (classically in very early meningococcal meningitis or in extremely ill neonates)
  • Lymphocytosis with normal CSF chemistry results observed in 15-25% of patients, especially if counts < 1000 or if patient is partially treated
  • About 90% of patients with ventriculoperitoneal shunts and CSF WBC count >100 cells/µL are infected, though CSF glucose level often normal, and bacteria often less pathogenic
  • Cell count and chemistry levels normalize slowly (days) with antibiotics
  • Usually < 500, nearly 100% mononuclear
  • < 48 hours, clinically significant polymorphonuclear pleocytosis may be indistinguishable from early bacterial meningitis, particularly with EEE
  • Nontraumatic RBCs in 80% of patients with HSV meningoencephalitis, though 10% have normal CSF results
  • 100s of mononuclear cells
Microorganisms (none)
  • Gram stain 80% effective
  • Inadequate decolorization may cause Haemophilus influenzae to be mistaken for gram-positive cocci
  • Pretreatment with antibiotics may affect stain uptake, causing gram-positive species to appear to be gram-negative and decrease culture yield by an average of 20
  • No organism
  • India ink 80-90% effective for detecting fungi
  • AFB stain 40% effective for TB; increase yield by staining supernatant from at least 5 mL of CSF
Glucose



Euglycemia (>50% serum)



Hyperglycemia (>30% serum)



  • Decreased
  • Normal
  • Sometimes decreased
  • In addition to fulminant bacterial meningitis, TB, primary amebic meningoencephalitis, and neurocysticercosis cause low glucose levels
Protein



Preterm (65-150 mg/dL)



Term (20-170 mg/dL



6 mo+ (15-45 mg/dL)



  • Usually >150 mg/dL
  • May be >1000 mg/dL
  • Mildly increased
  • Increased >1000 mg/dL, with relatively benign clinical presentation suggestive of fungal disease
*Some bacteria (eg, Mycoplasma, Listeria, Leptospira, Borrelia burgdorferi [Lyme disease]) cause alterations in spinal fluid that resemble the viral profile. An aseptic profile is also typical of partially treated bacterial infections (>33%, especially those in children, are treated with antimicrobials) and of the 2 most common causes of encephalitis—the arboviruses and the potentially curable HSV.



Wait 4 hours after glucose load.



AFB—acid-fast bacillus; CSF—cerebrospinal fluid; EEE-eastern equine encephalitis; HSV—herpes simplex virus; RBC—red blood cell; TB—tuberculosis; WBC—white blood cell.



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