Encephalitis Differential Diagnoses

Author: David S Howes, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP more...

Updated: Jan 6, 2012

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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

Proceed to Workup

Contributor Information and Disclosures

Author

David S Howes, MD Professor of Medicine and Pediatrics, Emergency Medicine Residency Program Director Emeritus, Head, Phemister Society, University of Chicago Division of the Biological Sciences, 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, American College of Physicians-American Society of Internal Medicine, and 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 College of Emergency Physicians, American Medical Informatics Association, and 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, 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 Academy of Emergency Medicine, American College of Chest Physicians, American College of Emergency Physicians, American College of Physicians, American Heart Association, American Thoracic Society, Arkansas Medical Society, New York Academy of Medicine, New York Academy of Sciences, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Additional Contributors

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

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.
MacDonald RD, Krym VF. West Nile virus. Primer for family physicians. Can Fam Physician. Jun 2005;51:833-7. [Medline].
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. Mar 2009;65(3):257-67. [Medline].
Bloch KC, Glaser C. Diagnostic approaches for patients with suspected encephalitis. Curr Infect Dis Rep. Jul 2007;9(4):315-22. [Medline].
[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. Aug 1 2008;47(3):303-27. [Medline].

Table. Cerebrospinal Fluid Findings by Type of Organism

Table. Cerebrospinal Fluid Findings by Type of Organism

CSF Finding (Normal)	Bacterial Meningitis	Viral 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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