Rosen & Barkin's 5-Minute Emergency Medicine Consult (784 page)

• CSF:
  
  • Pleocytosis with lymphocyte predominance
    
  • Elevated protein
    
  • Normal glucose
    
• CBC:
  
  • WBCs may be mildly elevated (50%) or normal.
    
  • Leukopenia may be present (15%).
    
  • Anemia can occur.
    
• Chemistry:
  
  • Hyponatremia sometimes seen:
    
    • Cause uncertain, possibly syndrome of inappropriate antidiuretic hormone (SIADH) when CNS involvement exists
      
  • Pancreatitis (rare)
    
  • Fulminant hepatitis (rare)
    

• CT head usually normal
  
• MRI can be useful to identify CNS inflammation:
  
  • 1/3 of patients show abnormality.
    
  • Imaging findings generally nonspecific but may include enhancement of leptomeninges and/or periventricular white matter or can mimic demyelinating process.
    

• Lumbar puncture
  
• MAC-ELISA may be used on serum and CSF samples
  

• Other causes of meningitis:
  
  • Bacterial
    
  • Viral
    
  • Tuberculous
    
  • Fungal
    
• Other causes of viral encephalitis:
  
  • Other arboviruses, especially St. Louis encephalitis virus
    
  • Enterovirus, particularly in patients ≤16 yr of age
    
  • Herpes simplex virus (HSV)
    
  • Cytomegalovirus (CMV)
    
  • Epstein–Barr virus (EBV)
    
  • Mumps virus
    
  • Varicella zoster virus
    
  • Rabies virus
    
• Intracranial abscess
  
• CNS vasculitis
  
• Nonspecific viral syndrome
  
• Gastroenteritis
  

TREATMENT

• ABCs
  
• Seizure precautions
  

• Supportive care
  
• IV fluids for signs of dehydration
  
• For signs of meningitis, administer antibiotics pending results of CSF.
  
• Consider acyclovir if index of suspicion for the only treatable cause of viral encephalitis, HSV, is high.
  
• Administer antipyretics and pain medications.
  
• No known effective antiviral therapy or vaccine
  
• No controlled studies proving effectiveness of interferon α-2b, ribavirin, corticosteroids, anticonvulsants, or osmotic agents
  

FOLLOW-UP

• Neurologic symptoms
  
• Dehydration
  
• Concerning risk factors (advanced age, immunocompromise)
  

• No signs of CNS involvement (encephalitis, meningitis)
  
• Able to tolerate oral solutions
  

Neurologist to monitor for potential ongoing residual.

Consider HSV in differential, since HSV is treatable.

• Centers for Disease Control and Prevention (CDC): Interim guidelines for the evaluation of infants born to mothers infected with West Nile Virus during pregnancy.
  MMWR Morb Mortal Wkly Rep.
  2004;53:154–157.
  
• Hayes EB, O’Leary DR. West Nile virus infection: A pediatric perspective.
  Pediatrics
  . 2004;113:1375–1381.
  
• Loeb M, Hanna S, Nicolle L, et al. Prognosis after West Nile virus infection.
  Ann Intern Med.
  2008;149:232–241.
  
• Petersen LR, Marfin AA, Gubler DJ. West Nile virus.
  JAMA.
  2003;290:524–528.
  
• Peterson LR, Hayes EB: West Nile virus in the Americas.
  Med Clin North Am.
  2008;92:1307–1322.
  
• West Nile Virus: Information and Guidance for Clinicians. Available at
  http://www.cdc.gov/ncidod/dvbid/westnile/clinicians
  
• Zak IT, Altinok D, Merline JR, et al. West Nile virus infection.
  AJR Am J Roentgenol.
  2005;184(3):957–961.
  

See Also (Topic, Algorithm, Electronic Media Element)

Meningitis; Encephalitis, HSV

CODES

• 066.40 West Nile Fever, unspecified
  
• 066.41 West Nile Fever with encephalitis
  
• 066.42 West Nile Fever with other neurologic manifestation
  

BASICS

• Result of turbulent airflow:
  
  • High-pitched sound with dominant frequency at 400 Hz:
    
    • Gas flowing through constricted airways analogous to a vibrating reed
      
  • Resonant vibration of the bronchial walls when airflow velocity reaches critical values
    
• Caused by airway narrowing between 2–5 mm:
  
  • Wheezing is very low pitched with airway diameters of 5 mm.
    
  • Airways of <2 mm are unable to transmit sound because the energy is lost as friction heat.
    
• Airway narrowing is caused by a combination of ≥1 of the following:
  
  • Constriction (as with reactive airway disease)
    
  • Peribronchial interstitial edema
    
  • Inflammation
    
  • Obstruction
    

• Pulmonary (small airway):
  
  • Asthma
    
  • Acute respiratory distress syndrome
    
  • Anaphylaxis
    
  • Aspiration pneumonia:
    
    • Wheezing occurs early in the disease due to intense bronchospasm following the event.
      
  • Byssinosis:
    
    • Occupational lung disease of textile workers exposed to cotton dust
      
  • Drugs:
    
    • Can precipitate angioedema or allergic reaction
      
    • ACE inhibitors
      
    • β-blockers
      
    • Aspirin and NSAIDs
      
  • Forced exhalation in normal patients
    
  • Hyperventilation
    
  • Chronic obstructive pulmonary disease
    
  • Chronic cor pulmonale
    
  • Chemical pneumonitis
    
  • Carcinoid tumors
    
  • Paroxysmal nocturnal dyspnea
    
  • Pulmonary edema
    
  • Pulmonary embolism:
    
    • Rarely associated with wheezing
      
    • Focal
      
  • Pneumonia
    
  • Sleep apnea
    
• Pulmonary (large airway):
  
  • Vocal cord dysfunction (paralysis, paradoxical movement)
    
  • Foreign body
    
  • Epiglottitis:
    
    • Wheezing associated with stridor in 10% of cases
      
  • Diphtheria
    
  • Smoke inhalation
    
  • Bronchial tumor
    
  • Tracheal tumor
    

• Viral bronchiolitis in patients <3 yr of age
  
• Asthma
  
• Infection:
  
  • Croup
    
  • Rhinovirus
    
• Foreign-body aspiration
  
• Congenital abnormalities:
  
  • Tracheomalacia
    
  • Tracheal stenosis
    
• Cystic fibrosis
  
• CHF
  

DIAGNOSIS