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a. Herpesvirus-1 (HSV-1) Make your selection before scrolling beyond this point Answer: In the United States, common causes of acute viral encephalitis in normal hosts include herpesvirus-1 (HSV-1), which is transmitted person-to-person, and the arboviruses, which are mosquito-transmitted and include California encephalitis (CE), Western equine encephalitis (WEE), Venezuelan equine encephalitis (VEE), Eastern equine encephalitis (EEE), St. Louis encephalitis (SLE), Japanese encephalitis (JE), and West Nile encephalitis (WNE), among others. CMV and Toxoplasma encephalitis are almost always seen in compromised hosts (e.g., solid organ transplants, HIV/AIDS), not normal hosts, and Toxoplasma gondii is a parasite, not a virus. (Answer: a, b, c) 2. All of the following are acceptable forms of initial empiric therapy for acute encephalitis except: a. Herpesvirus-1 (HSV-1): acyclovir Make your selection before scrolling beyond this point Answer: Herpes encephalitis is treated with acyclovir 10 mg/kg (IV) q8h x 7 days, followed by acyclovir 400 mg (PO) 5x/day or valacyclovir 1 gm (PO) q8h or famciclovir 500 mg (PO) q8h (if able to take oral medication) to complete 14-21 days of total therapy. Early administration of acyclovir has reduced the fatality rate from 75% to less than 30%. CMV encephalitis is treated with ganciclovir 5 mg/kg (IV) q12h x 3 weeks, followed by valganciclovir 900 mg (PO) q24h (indefinitely unless immune reconstitution occurs in HIV/AIDS patients). For severe cases, consider ganciclovir + foscarnet. Preferred treatment for toxoplasma encephalitis consists of 6-8 weeks of sulfadiazine 1.5-2 gm (PO) q6h + pyrimethamine 200 mg (PO) x 1 dose then 50 mg (PO) q6h + folinic acid 10 mg (PO) q24h, until good clinical response, followed by life-long suppressive therapy (unless immune reconstitution occurs in HIV/AIDS patients) with sulfadiazine 1 gm (PO) q12h + pyrimethamine 50 mg (PO) q24h + folinic acid 10 mg (PO) q24h. There is no specific treatment for St. Louis encephalitis, West Nile encephalitis, or other arboviral encephalitides. (Answer: a, d, e) 3. Typical cerebrospinal fluid (CSF) findings in acute viral encephalitis include: a. WBC count 500-5000 cells/mm3 Make your selection before scrolling beyond this point Answer: CSF analysis is an important diagnostic tool in the approach to the patient with suspected CNS infection. Typical findings in acute viral encephalitis are similar to aseptic meningitis and include a mild to moderately elevated WBC count of 25-250 cells/mm3 (PMNs early, monocytes by day 2-3), normal or slightly elevated opening pressure (usually < 250 mm H20), mildly elevated (50-100 mg/dL), and normal glucose levels (50-70% of serum glucose levels). In contrast, typical findings in acute bacterial meningitis include a WBC count of 100-5000 cells/mm3 (predominantly PMNs), elevated opening pressure (< 300 mm H2O in 70%; >300 mm H2O in 30%), elevated protein levels in 95% (> 200 mg/dL in 50%), elevated lactic acid levels (> 6 mmol/L), and a positive CSF gram stain in 60-90%, depending on the organism. (Answer: c, d) 4. Which of the following statements about herpes (HSV-1) encephalitis are true: a. Unlike other causes of viral
encephalitis, CSF analysis may have PMN predominance (>90%) and low glucose levels Make your selection before scrolling beyond this point Answer: Herpes encephalitis presents with the acute onset of fever and change in mental status without nuchal rigidity. EEG is the best early (< 72 hours) presumptive test, showing unilateral temporal lobe abnormalities. Brain MRI is abnormal before CT scan, which may require several days before a temporal lobe focus is seen. Definitive diagnosis is by CSF PCR for HSV-1 DNA; culture of CSF for HSV is negative. Profound decrease in sensorium is characteristic of HSV encephalitis. CSF analysis may have PMN predominance (>90%) and low glucose levels, unlike other viral causes of meningitis. HSV is the only treatable common cause of viral encephalitis in normal hosts. Treatment with acyclovir should begin as soon as possible, since neurological deficits may be mild and reversible early on, but severe and irreverisible later. (Answer: a, d, e) 5. Which of the following statements about other forms of acute encephalitis are true: a. Effective vaccine is available for the
prevention of Japanese B encephalitis Make your selection before scrolling beyond this point Answer: Arboviral encephalitis presents with acute onset of fever, headache, change in mental status days to weeks after inoculation of virus through the bite of an infected insect (e.g., mosquito/tick). Diagnosis is suggested by arboviral contact/travel history, and is confirmed by specific arboviral serology. The risk of Japanese B encephalitis can be reduced with administration of vaccine; however, once arboviral encephalitis occurs , only supportive therapy is available. Mycoplasma encephalitis presents with acute onset of fever and change in mental status without nuchal rigidity, and usually occurs as a complication of pulmonary infection (although CNS findings may overshadow pulmonary findings). Diagnosis is suggested by CNS and extra-pulmonary manifestations—sore throat, otitis, E. multiforme, soft stools/diarrhea—in a patient with community-acquired pneumonia, elevated IgM Mycoplasma titers, and very high (> 1:1024) cold agglutinin titers. CSF shows mild mononucleosis/pleocytosis and normal/low glucose. With early treatment, prognosis is good without neurologic sequelae. Toxoplasma encephalitis can present with a wide spectrum of neurologic symptoms, including sensorimotor deficits, seizures, confusion, ataxia; fever and headache are common. Affected patients usually respond to treatment if able to tolerate drugs. Clinical response is evident by 1 week in 70%, by 2 weeks in 90%. CMV encephalitis presents with fever, mental status changes, and headache evolving over 1-2 weeks. True meningismus is rare. CMV encephalitis occurs in advanced HIV disease (CD4 < 50/mm3), often in patients with prior CMV retinitis. Characteristic findings on brain MRI include confluent periventricular abnormalities with variable degrees of enhancement. Diagnosis is confirmed by CSF CMV PCR (preferred), CMV culture, or brain biopsy. An ophthalmologic evaluation should be performed to exclude active retinitis. Unless immune reconstitution occurs, response to ganciclovir is usually transient, followed by progression of symptoms. (Answer: a, c, d) 6. Which pathogens are commonly associated brain abscess from the following sources: a. Neurosurgical procedure: S. aureus, S.
epidermidis Make your selection before scrolling beyond this point Answer: The microbiology of brain abscess depends on the presence of predisposing conditions. Usual pathogens include S. aureus/S. epidermidis following neurosurgical procedures, Enterobacter/Proteus with mastoid or otitic sources, oral anaerobes/Actinomyces with dental or pulmonary sources, oral anaerobes/H. influenzae with subdural empyema or sinus sources, and S. aureus/S. pneumoniae/H. influenzae from cardiac sources (e.g., acute bacterial endocarditis; right-to-left shunt). CNS involvement in subacute bacterial endocarditis usually results in aseptic meningitis, not brain abscess, due to the relative low virulence of pathogens compared to acute bacterial endocarditis. Brain abscess may complicate pulmonary suppurative processes (e.g., lung abscess/empyema, bronchiectasis), but is not a complication of chronic bronchitis. (Answer: all except c) 7. Which of the following statements about brain abscess are true: a. Most patients present with fevers,
altered mental status, and cranial nerve abnormalities Make your selection before scrolling beyond this point Answer: The presentation of brain abscess is variable, with fever, change in mental status, cranial nerve abnormalities, mass effect ± headache. If brain abscess is suspected, head CT/MRI should be obtained; lumbar puncture may induce herniation and should be avoided. Diagnosis is confirmed by CSF gram stain/culture of abscess, although organisms isolated from blood, sinuses, or empyema can be very helpful in initial selection of antimicrobials. CSF analysis is negative for bacterial meningitis unless the abscess ruptures into the ventricular system. Treatment with meningeal doses of antibiotics is required. Large single abscesses may be surgically drained (in conjunction with antimicrobial therapy); multiple small abscesses are best treated medically. (Answer: a, d)
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