II. Causes: Viral (most cases)
- Causative organism identified in only half of cases
- Common
- Enterovirus Meningitis (50.9% of all Meningitis cases in adults)
- Herpes Simplex Encephalitis (8.3% of all Meningitis cases in adults, Very poor prognosis)
- Adults: Herpes Simplex Virus I
- Neonates: Herpes Simplex Virus II
- Varicella Zoster Virus (15% of cases)
- Mumps (Generally benign)
- Arbovirus (1.1% of all Meningitis causes in adults)
- Eastern equine Encephalitis (70-90% poor prognosis)
- Western equine Encephalitis (2-20% poor prognosis)
- St. Louis Encephalitis (2-20% poor prognosis)
- Powassan Encephalitis (Tick Borne Illness, 50% with Cognitive Impairment, 10-15% mortality)
- California Encephalitis (generally benign)
- Venezuelan equine Encephalitis (generally benign)
- West Nile Virus Encephalitis (severe in elderly)
- Japanese Encephalitis (severe disease is uncommon, but 30% mortality when it occurs)
- Limited to travelers to rural and periurban Southeast Asia, Western Pacific
- Uncommon
- Parvovirus B19
- Epstein-Barr Virus
- Influenza
- Rabies (rare in U.S.)
- Immunocompromised
III. Causes: Other non-viral (uncommon)
- Bacterial causes
- Fungal causes
- Cryptococcus
- Coccidioides
- Histoplasma
- Parasitic causes
- Miscellaneous causes
- NMDA Encephalitis (very common in age <30 years old)
IV. Symptoms
- Sudden high fever
- Severe Headache
- Meningismus (e.g. Stiff neck)
-
Altered Level of Consciousness
- Lethargy
- Mental confusion
- Coma
- Behavior change
- Seizure
- Dysarthria
- Dysphasia
- Nausea and Vomiting
- Photophobia
- Hemiparesis
- Cranial Nerve deficits
- Visual Field loss
V. Signs
- Variable signs depending on involvement and organism
- See HSV Encephalitis
- See West Nile Virus Encephalitis (C0043124)
-
Tremor
- Tongue
- Lips
- Hands
- Other neurologic changes
- Ataxia
- Spastic paralysis
- Deep Tendon Reflexes exaggerated
- Signs of Increased Intracranial Pressure
VI. Differential Diagnosis
VII. Labs
- See Altered Level of Consciousness for general labs
-
Complete Blood Count (CBC)
- Mild Leukocytosis
- Mild Lymphocytosis
- Serum Electrolytes and Glucose
- Specific testing
- Strep Throat swab
- Influenza nasal swab
- St Loius Encephalitis serum IgM
- West Nile Virus serum IgM
- Western Equine Encephalitis serum IgM
- Mycoplasma pneumoniae IgM
- Lyme Disease Screening
- Serum RPR for Syphilis
- CMV culture from urine or Saliva (Test Sensitivity approaches 100%)
- Varicella culture from vessicles
- Herpes culture from Vesicles, mucous membranes and urine
- Cerebrospinal Fluid (CSF)
- Initial tests
- CSF Gram Stain
- CSF Culture
- CSF Protein
- CSF Glucose
- CSF Cell Count with differential
- Typical non-specific findings
- Increased Intracranial Pressure
- Increased Protein
- Lymphocytic Pleocytosis
- CSF Antigens (indicated if CSF findings not consistent with Bacterial Meningitis)
- CSF HSV PCR (Send in all cases of suspected Encephalitis)
- CSF enterovirus PCR
- Initial tests
VIII. Imaging
-
CT Head
- Indicated prior to Lumbar Puncture if focal neurologic findings or signs of Increased Intracranial Pressure
-
MRI Brain
- See HSV Encephalitis for HSV specific findings
- CMV Encephalitis
- Periventricular intracranial calcifications
- Cerebral dysgenesis
-
Congenital Toxoplasmosis
- Multiple ring-enhancing lesions
-
Cysticercosis
- Cystic lesions with variable calcifications
- Ring enhancement suggests cyst degeneration
IX. Management
- Empiric HSV management
- Cerebral Edema
- Mannitol
- Corticosteroids
- Only for specific indications
- Avoid in Herpes Simplex Virus
- Seizure control
- Specific empiric Management if cause suspected (Keep high level of suspicion for treatable etiologies)
- HSV Encephalitis
- Acyclovir IV (see dosing above)
- CMV Encephalitis (AIDS)
- Rocky Mountain Spotted Fever
- Doxycycline for any age where this is strongly suspected (causes tooth staining in under age 8 years)
- Cat-Scratch Disease Encephalitis
- Mycoplasma pneumoniae Encephalitis
- Lyme Encephalitis
- Ceftriaxone 75-100 mg/kg up to 2 grams IV q24 hours
- Influenza Encephalitis
- HSV Encephalitis
X. Course
- Symptomatic: weeks to months
XI. Prognosis
- Mortality during acute illness: 10%
- High rate of Disability following infection
- Variable depending on specific etiology
XII. References
- (2016) Sanford Guide, accessed 4/11/2016
- Fuchs and Yamamoto (2012) APLS, Jones and Bartlett, Burlington, p. 180-3
- Mailles (2009) Clin Infect Dis 49(12):1838-47 +PMID:19929384 [PubMed]
- Singh (2015) Neurology 84(4):359-66 +PMID:25540320 [PubMed]