What is the standard of care for diagnosing meningitis and encephalitis caused by the LaCrosse virus?

Standard of Care for Diagnosing Meningitis and Encephalitis Caused by LaCrosse Virus

The standard of care for diagnosing LaCrosse virus encephalitis requires a comprehensive diagnostic approach including cerebrospinal fluid (CSF) analysis with serologic testing for LaCrosse virus-specific IgM and IgG antibodies, neuroimaging preferably with MRI, and electroencephalogram (EEG). 1, 2

Diagnostic Algorithm

Initial Assessment

• Consider LaCrosse virus infection in patients presenting with encephalitis symptoms, particularly:
  • School-aged children (most common) or adults in endemic areas
  • Presentation during summer/fall seasons
  • History of mosquito exposure in endemic regions (28 states, primarily Midwestern and Eastern US)

Essential Diagnostic Tests

1. Cerebrospinal Fluid Analysis

   • Collect at least 20cc fluid when possible (5cc minimum in children)
   • Standard CSF studies:
     • Opening pressure
     • Cell count with differential (typically shows pleocytosis)
     • Protein and glucose levels
     • Gram stain and bacterial culture
   • Specific testing for LaCrosse virus:
     • Serologic testing for LaCrosse virus-specific IgM and IgG antibodies in CSF
     • PCR for viral RNA detection
     • Consider paired acute and convalescent serum samples 10-14 days apart 1

2. Neuroimaging

   • MRI is preferred over CT for suspected viral encephalitis 1, 2
   • Important findings:
     • May show temporal lobe abnormalities that can mimic herpes simplex encephalitis 3, 4
     • Signal abnormalities in frontotemporal regions

3. Electroencephalogram (EEG)

   • May show:
     • Periodic lateralizing epileptiform discharges (PLEDs)
     • Generalized slowing
     • Seizure activity 1, 3

Additional Testing Based on Clinical Context

• Serum studies:
  • LaCrosse virus IgM and IgG antibodies
  • Complete blood count
  • Metabolic panel (monitor sodium levels - hyponatremia is common) 5, 6
• Consider multiplex PCR panels that include LaCrosse virus 7

Clinical Features to Monitor

• Key symptoms that support diagnosis:
  • Fever, headache, vomiting (present in >70% of cases) 5
  • Seizures (46% of cases)
  • Altered mental status/disorientation (42% of cases)
  • Hyponatremia (21% of cases) - important marker for potential clinical deterioration 5, 6

Diagnostic Pitfalls and Considerations

1. Misdiagnosis risk: LaCrosse encephalitis can mimic herpes simplex encephalitis due to similar clinical presentation and neuroimaging findings 3, 4

2. Risk factors for clinical deterioration that should prompt more aggressive monitoring:

   • Hyponatremia
   • Increasing body temperature
   • History of vomiting
   • Glasgow Coma Scale score ≤12
   • Seizures at presentation 5

3. Seasonal and geographic considerations:

   • Testing should be prioritized during summer/fall seasons
   • Consider in endemic areas (Midwestern and Eastern United States) 1

4. Differential diagnosis must include:

   • Herpes simplex encephalitis (requires empiric acyclovir until ruled out)
   • Other arboviral encephalitides
   • Autoimmune encephalitis
   • Bacterial meningitis 1, 2

By following this diagnostic approach, clinicians can accurately diagnose LaCrosse virus encephalitis and distinguish it from other causes of encephalitis, particularly herpes simplex encephalitis, which requires different treatment.