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Central Nervous System lnfections Mosquito-borne viruses such as West Nile virus (WNV), Lyme disease, caused by Borreliaburgdorferi, can present St. Louis encephalitis, and California encephalitis can cause with a lymphocytic meningitis approximately 2 to 10 weeks meningitis or encephalitis between June and October in the after erythema migrans develops. Common clinical features Western Hemisphere. Neuroinvasive WNV may present with include headache, photophobia, nausea, history of erythema acute flaccid paralysis, potentially leading to persistent weak- migrans, tick bite in an endemic area, and facial paralysis, ness or death. The CSF formula resembles enteroviral menin- which can be unilateral or bilateral. gitis. The diagnosis is made by serum or CSF serologz (WNV Treponema pallidum meningitis can occur in the sec IgM). Treatment is suPPortive. ondary or tertiary phase of syphilis. Headache and meningis Acute HIV infection can present as aseptic meningitis mus are common, and the CSF usually shows a lymphocytic associated with a mononucleosis like syndrome with fever, pleocytosis with an elevated protein level. In tertiary syphilis, rash, and myalgia. neurosyphilis can be asymptomatic or symptomatic' Less common viral causes include mumps, lymphocytic Symptomatic neurosyphilis can present with primarily choriomeningitis virus, parainfluenza, adenoviruses, influ- meningovascular (stroke presentation) or parenchymatous enza A and B, measles, rubella, poliovirus, rotavirus, and (tabes dorsalis, general paresis) features. parvovirus B19. Leptospiral meningitis develops in the immune or second phase of the illness and is classically associated with uveitis, I(EY PO I ilTS rash, conjunctival suffusion, lymphadenopathy, and hepato o Enteroviruses are the most common cause of viral splenomegaly. The CSF formula resembles enteroviral menin meningitis, usually presenting with symptoms of gitis, and the diagnosis is established by CSF or urine culture headache, fever, nuchal rigidity, photophobia, nausea, or by serologz. vomiting, myalgia, pharyngitis, maculopapular rash, and cough between May and November in the Western Evaluation Hemisphere. A11 patients with suspected meningitis should promptly o Herpesviruses can cause meningitis year round; herpes undergo LP because a delay is associated with increased costs simplex virus 2 is the most common cause and can and a decrease in the yield of the CSF culture. CSF findings recur. characteristic of bacterial meningitis are provided in Table 1. o Neuroinvasive West Nile virus may present with acute A negative CSF Gram stain result is more common in patients flaccid paralysis, which may lead to persistent weakness with previous antibiotic therapy or in patients with L. mono- or death. cytogenes or gram-negative bacilli (sensitiviff <50'2,) infec- tions. CSF latex agglutination tests for detecting bacterial antigens are no longer recommended. S. pneumonioe anti Bacterial Meningitis gen detection in the CSF has a 99% sensitivity and specificity. Bacterial meningitis usually presents with acute meningeal A multiplex PCR assay that can detect 14 pathogens in t hour signs (fever, nuchal rigidity) and altered mental status. The is also now available. If a head CT is indicated before LP (focal incidence of Haemophilus influenzae, Neisseria menin neurologic findings, altered mental status, papilledema, new gitidis, and Streptococcus pneumonioe meningitis have seizure, history of CNS disease, or immunocompromise), decreased; however, S. pneumoniae remains the most com- imaging should not delay empiric antibiotic therapy, which mon cause of community acquired bacterial meningitis. I{. should be started after promptly obtaining blood cultures. meningitidis serogroup B accounts for 40% of infections in See Figure I for management of suspected bacterial the United States because the quadrivalent conjugate vaccine meningitis. (ACYW-135) does not include serogroup B. Two FDA- approved vaccines that target serogroup B are available in the Management United States. Listeria monocytogenes is an uncommon Intravenous antibiotic therapy should be started as soon as cause of meningitis in adults; however, the risk increases in possible. If the CSF Gram stain result is negative, initial patients older than 50 years and those with altered cell empiric antibiotic selection is based on age, local epide- mediated immunity. miologic patterns of pneumococcal resistance, and the Bacterial endocarditis caused by S. pneumonioe and necessity for ampicillin coverage for L. monocgtogenes Staphylococcus aureus can present as purulent meningi- (Table 2). Despite antibiotic therapy, mortality for bacterial tis. Clinical clues include a history of valvular disease, a meningitis remains approximately 25%. Adjunctive dexa- new regurgitant murmur, embolic phenomena, or other methasone, given concomitantly with the first dose of stigmata of endocarditis. Injection drug use and hemodi- antibiotic therapy, reduces morbidity and mortality in alysis are risk factors for S. aureus, and alcoholism is a risk adults with pneumococcal meningitis in developed coun- factor for S. pneumonioe endocarditis. Patients may also tries. In patients with an identified cause, dexamethasone present with stroke symptoms secondary to embolic treatment should be limited to those with S. pneumoniae infarction. meningitis.

Mosquito-borne viruses such as West Nile virus (WNV), Lyme disease, caused by Borreliaburgdorferi, can present St. Louis encephalitis, and California encephalitis can cause with a lymphocytic meningitis approximately 2 to 10 weeks meningitis or encephalitis between June and October in the after erythema migrans develops. Common clinical features Western Hemisphere. Neuroinvasive WNV may present with include headache, photophobia, nausea, history of erythema acute flaccid paralysis, potentially leading to persistent weak- migrans, tick bite in an endemic area, and facial paralysis, ness or death. The CSF formula resembles enteroviral menin- which can be unilateral or bilateral. gitis. The diagnosis is made by serum or CSF serologz (WNV Treponema pallidum meningitis can occur in the sec IgM). Treatment is suPPortive. ondary or tertiary phase of syphilis. Headache and meningis Acute HIV infection can present as aseptic meningitis mus are common, and the CSF usually shows a lymphocytic associated with a mononucleosis like syndrome with fever, pleocytosis with an elevated protein level. In tertiary syphilis, rash, and myalgia. neurosyphilis can be asymptomatic or symptomatic' Less common viral causes include mumps, lymphocytic Symptomatic neurosyphilis can present with primarily choriomeningitis virus, parainfluenza, adenoviruses, influ- meningovascular (stroke presentation) or parenchymatous enza A and B, measles, rubella, poliovirus, rotavirus, and (tabes dorsalis, general paresis) features. parvovirus B19. Leptospiral meningitis develops in the immune or second phase of the illness and is classically associated with uveitis, I(EY PO I ilTS rash, conjunctival suffusion, lymphadenopathy, and hepato o Enteroviruses are the most common cause of viral splenomegaly. The CSF formula resembles enteroviral menin meningitis, usually presenting with symptoms of gitis, and the diagnosis is established by CSF or urine culture headache, fever, nuchal rigidity, photophobia, nausea, or by serologz. vomiting, myalgia, pharyngitis, maculopapular rash, and cough between May and November in the Western Evaluation Hemisphere. A11 patients with suspected meningitis should promptly o Herpesviruses can cause meningitis year round; herpes undergo LP because a delay is associated with increased costs simplex virus 2 is the most common cause and can and a decrease in the yield of the CSF culture. CSF findings recur. characteristic of bacterial meningitis are provided in Table 1. o Neuroinvasive West Nile virus may present with acute A negative CSF Gram stain result is more common in patients flaccid paralysis, which may lead to persistent weakness with previous antibiotic therapy or in patients with L. mono- or death. cytogenes or gram-negative bacilli (sensitiviff <50'2,) infec- tions. CSF latex agglutination tests for detecting bacterial antigens are no longer recommended. S. pneumonioe anti Bacterial Meningitis gen detection in the CSF has a 99% sensitivity and specificity. Bacterial meningitis usually presents with acute meningeal A multiplex PCR assay that can detect 14 pathogens in t hour signs (fever, nuchal rigidity) and altered mental status. The is also now available. If a head CT is indicated before LP (focal incidence of Haemophilus influenzae, Neisseria menin neurologic findings, altered mental status, papilledema, new gitidis, and Streptococcus pneumonioe meningitis have seizure, history of CNS disease, or immunocompromise), decreased; however, S. pneumoniae remains the most com- imaging should not delay empiric antibiotic therapy, which mon cause of community acquired bacterial meningitis. I{. should be started after promptly obtaining blood cultures. meningitidis serogroup B accounts for 40% of infections in See Figure I for management of suspected bacterial the United States because the quadrivalent conjugate vaccine meningitis. (ACYW-135) does not include serogroup B. Two FDA- approved vaccines that target serogroup B are available in the Management United States. Listeria monocytogenes is an uncommon Intravenous antibiotic therapy should be started as soon as cause of meningitis in adults; however, the risk increases in possible. If the CSF Gram stain result is negative, initial patients older than 50 years and those with altered cell empiric antibiotic selection is based on age, local epide- mediated immunity. miologic patterns of pneumococcal resistance, and the Bacterial endocarditis caused by S. pneumonioe and necessity for ampicillin coverage for L. monocgtogenes Staphylococcus aureus can present as purulent meningi- (Table 2). Despite antibiotic therapy, mortality for bacterial tis. Clinical clues include a history of valvular disease, a meningitis remains approximately 25%. Adjunctive dexa- new regurgitant murmur, embolic phenomena, or other methasone, given concomitantly with the first dose of stigmata of endocarditis. Injection drug use and hemodi- antibiotic therapy, reduces morbidity and mortality in alysis are risk factors for S. aureus, and alcoholism is a risk adults with pneumococcal meningitis in developed coun- factor for S. pneumonioe endocarditis. Patients may also tries. In patients with an identified cause, dexamethasone present with stroke symptoms secondary to embolic treatment should be limited to those with S. pneumoniae infarction. meningitis. 2

Central Nervous System lnfections Suspicion for bacterial men ingitis Yes lmmunocompromise, history of CNS disease, n ew-onset seizu re, pa p i I ledema, a ltered co nscio usn ess, or focal neurologic deficit or delay in performance of d iagnostic lumbar puncture No Yes Blood cultures and Blood cultures lumbar puncture emergently emergently Dexamethasone + empi ric Dexamethasone + empi ric antimicrobialtherapy antimicrobial therapy Negative CT scan of the head FIGU RE 1 . Managementalgorithm for CSF findings c/w bacterial meningitis Perform I umbar pu ncture adults suspected of having bacterial meningitis. CNS = central nervous system; Yes c/w = consistent with; CSF = cerebrospinal fluid.'Dexamethasone should be continued Positive CSF Gram stain for 4 days in patients with Streptococcus pneumoniae meningitis and stopped in all No Yes others.

FIGU RE 1 . Managementalgorithm for CSF findings c/w bacterial meningitis Perform I umbar pu ncture adults suspected of having bacterial meningitis. CNS = central nervous system; Yes c/w = consistent with; CSF = cerebrospinal fluid.'Dexamethasone should be continued Positive CSF Gram stain for 4 days in patients with Streptococcus pneumoniae meningitis and stopped in all No Yes others. Reprinted with permission from Tunkel AR, Hartman BJ, Kaplan SL, Kaufman BA, Roos KL, Scheld WM, et al. Practice Dexamethasone + empi ric Dexamethasonea + targeted guidelines forthe management of bacterial meningitis. Clin antimicrobial therapy antimicrobial therapy lnfect Dis. 2004;39:1267-84. IPMID: 15494903] Copyright 2004 Oxford University Press.

Reprinted with permission from Tunkel AR, Hartman BJ, Kaplan SL, Kaufman BA, Roos KL, Scheld WM, et al. Practice Dexamethasone + empi ric Dexamethasonea + targeted guidelines forthe management of bacterial meningitis. Clin antimicrobial therapy antimicrobial therapy lnfect Dis. 2004;39:1267-84. IPMID: 15494903] Copyright 2004 Oxford University Press. TABLI ?. Treatment of Bacterial Meningitis Clinical Characteristics Empiric Antibiotic Regimen" o For diagnosis of bacterial meningitis, the cerebrospinal lmmunocompetent host age lV ceftriaxone plus lV fluid (CSF) Gram stain result is positive in 60% to 90"/o <50 y with community- vancomycin of infections; the CSF Streptococcus pneumoniae anti- acquired bacterial meningitis gen detection test and a multiplex polymerase chain Age >50 y or those with lV ampicillin (Listeria coverage) reaction assay are preferred over latex agglutination altered cell-mediated plus lV ceftriaxone plus lV immunity vancomycin (in countries with testing for bacterial antigens. ceftriaxone resista nce rale >17", o Empiric intravenous antibiotic therapy and dexa- such as U.S.) methasone should be started as soon as possible Allergies to p-lactams lV moxifloxacin instead of when community-acquired bacterial meningitis is cephalosporin suspected; ceftriaxone plus vancomycin is indicated lVtrimethoprim- for patients 50 years or younger and ampicillin, cef* sulfamethoxazole instead of ampicillin triaxone, and vancomycin is indicated for patients older than 50 years or with altered cell-mediated Hea lth ca re-associated lVvancomycin plus either lV ventriculitis or meningitis ceftazidime, cefepi me, or immunity. meropenem . Adjunctive dexamethasone reduces morbidity and mor- lV = intravenous; U.S. = United States. tality in adults with pneumococcal meningitis and "Adjunctive dexamethasone should be given concomitantly with the first dose of reduces the risk of neurologic sequelae in bacterial antibiotic therapy and should be continued for 4 days in patients with Streptococcus pneumoniae meningitis and stopped in all others. meningitis in developed countries.

TABLI ?. Treatment of Bacterial Meningitis Clinical Characteristics Empiric Antibiotic Regimen" o For diagnosis of bacterial meningitis, the cerebrospinal lmmunocompetent host age lV ceftriaxone plus lV fluid (CSF) Gram stain result is positive in 60% to 90"/o <50 y with community- vancomycin of infections; the CSF Streptococcus pneumoniae anti- acquired bacterial meningitis gen detection test and a multiplex polymerase chain Age >50 y or those with lV ampicillin (Listeria coverage) reaction assay are preferred over latex agglutination altered cell-mediated plus lV ceftriaxone plus lV immunity vancomycin (in countries with testing for bacterial antigens. ceftriaxone resista nce rale >17", o Empiric intravenous antibiotic therapy and dexa- such as U.S.) methasone should be started as soon as possible Allergies to p-lactams lV moxifloxacin instead of when community-acquired bacterial meningitis is cephalosporin suspected; ceftriaxone plus vancomycin is indicated lVtrimethoprim- for patients 50 years or younger and ampicillin, cef* sulfamethoxazole instead of ampicillin triaxone, and vancomycin is indicated for patients older than 50 years or with altered cell-mediated Hea lth ca re-associated lVvancomycin plus either lV ventriculitis or meningitis ceftazidime, cefepi me, or immunity. meropenem . Adjunctive dexamethasone reduces morbidity and mor- lV = intravenous; U.S. = United States. tality in adults with pneumococcal meningitis and "Adjunctive dexamethasone should be given concomitantly with the first dose of reduces the risk of neurologic sequelae in bacterial antibiotic therapy and should be continued for 4 days in patients with Streptococcus pneumoniae meningitis and stopped in all others. meningitis in developed countries. 3

Central Nervous System lnfections TABLE 4. Predisposing Conditions, Causative Ag ents, and Empiric Antimicrobial Therapy in Patients with Bacteri al Brain Abscess Predisposing Condition Usual Causative Agents Empiric Antimicrobial TheraPY Otitis media or mastoiditis Streptococci (aerobic or anaerobic), Metronidazole plus a third-generation Ba cte roi d es species, Prev ote I a species, I cephalosporin" Enterobacteriaceae Sin usitis Stre ptococ ci, B a cte roi des s peci es, Metronidazole plus a third-generation Enterobacteriaceae, Sta phylococcu s a u reu s, cepha losporin''b Haemophilus species Dentalsepsis Mixed Fusobacterium, Prevotella, and Penicillin plus metronidazole Bacte roi d es speci es; stre ptococci Penetrating trauma or after neurosurgery S. aureus, streptococci, Pseudomonas, Vancomycin plus an antipseudomonal Enterobacteriaceae, Cl ostridi u m species B-lactam' Lung abscess, empyema, bronchiectasis Fu sob a cte ri u m, Acti n o myce s, B a cte roi d e s, Penicillin plus metronidazole plus a and Prevotel/a species; streptococci ; sulfonamided Nocardia species Endocarditis S. aureus, streptococci Vancomycin or daptomycin

Penetrating trauma or after neurosurgery S. aureus, streptococci, Pseudomonas, Vancomycin plus an antipseudomonal Enterobacteriaceae, Cl ostridi u m species B-lactam' Lung abscess, empyema, bronchiectasis Fu sob a cte ri u m, Acti n o myce s, B a cte roi d e s, Penicillin plus metronidazole plus a and Prevotel/a species; streptococci ; sulfonamided Nocardia species Endocarditis S. aureus, streptococci Vancomycin or daptomycin Hematogenous spread from pelvic, intra- Enteric gram-negative bacteria, a naerobic Metronidazole plus a third-generation abdominal, or gynecologic infections bacteria cephalospor;na,b'c I mmunocom promised patients Listeria species, fungal organisms Metronidazole plus a third-generation (Cryptococcus neoformans), or parasitic or cephalosporina'b'c'd'e' antifungal or HIV-infected patients protozoa I orga n isms (Toxopl asm a go ndii); antiparasitic agent Aspergillus, Coccidioides, and Nocardia species "Ceftriaxone; the fourth-generation cephalosporin cefepime may also be used. nafcillinf penicillin if methicillin-sensitive 5. aureus is confirmed. 'Use ceftazidime, cefepime, or meropenem lor Pseudomonas aeruginosa pending abscess cultures. dUse trimethoprim-sulfamethoxazole if infection caused by Nocardia species is suspected. "Use ampicillin if infection caused by Listeria species is suspected. lf allergic to penicillin, use trimethoprim-sulfamethoxazole.

'Use ceftazidime, cefepime, or meropenem lor Pseudomonas aeruginosa pending abscess cultures. dUse trimethoprim-sulfamethoxazole if infection caused by Nocardia species is suspected. "Use ampicillin if infection caused by Listeria species is suspected. lf allergic to penicillin, use trimethoprim-sulfamethoxazole. NOTE: lf predisposing condition is unknown, empiric treatment should include vancomycin plus metronidazole and a third-generation cephalosporin.

'Use ceftazidime, cefepime, or meropenem lor Pseudomonas aeruginosa pending abscess cultures. dUse trimethoprim-sulfamethoxazole if infection caused by Nocardia species is suspected. "Use ampicillin if infection caused by Listeria species is suspected. lf allergic to penicillin, use trimethoprim-sulfamethoxazole. NOTE: lf predisposing condition is unknown, empiric treatment should include vancomycin plus metronidazole and a third-generation cephalosporin. procedures (spinal fusion, epidural catheter placement) or Acute Flaccid Myelitis paraspinal injection. Patients usually develop localized pain Acute flaccid myelitis, first reported in 2014, presents as acute- at the site of infection that later radiates down the spine. onset limb weakness, often preceded by respiratory illness or MRI is the imaging modality of choice to identify location fever within the previous 4 weeks. It occurs most often in the and extent of the abscess. All patients should undergo a pediatric population but has been reported in adults. Several baseline laboratory evaluation, including erythrocyte sedi- neuroinvasive enteroviruses have been implicated, including mentation rate and C-reactive protein. Blood cultures EV-A71 and EV-D68. Outbreaks have occurred every 2 years should be obtained before starting antibiotics. Treatment (late summer and early fall) since 2074, and intensive surveil- should be at least 6 weeks of effective antimicrobial therapy. lance is ongoing in the United States. Acute flaccid myelitis can Surgical drainage is indicated in patients with neurologic progress rapidly and may be complicated by respiratory fail- symptoms or signs (lower extremity weakness, numbness, ure, so all patients should be hospitalized initially for close bladder and bowel dysfunction). Follow-up MRI is not indi- monitoring. The CDC has developed interim recommenda- cated unless the patient has persistent elevation of inflam tions for management; however, no evidence has shown any matory markers, lack of clinical response, or new neuro- current therapies affect outcomes. logic symptoms or signs. Tuberculosis (Pott disease) and brucellosis should be considered in patients with negative culture results and appropriate travel history and risk Encephalitis factors. Encephalitis is inflammation of the brain parenchyma. t(tY Ioll{T Probable or conflrmed encephalitis is defined by the presence . MRI is the imaging modality of choice to identify loca- of one major (altered consciousness for more than 24 hours) and at least three minor criteria (fever, new-onset seizure, tion and extent of a spinal epidural abscess, and blood new-onset focal neurologic findings, CSF pleocytosis, and cultures should be obtained before starting antibiotic abnormal MRI or electroencephalographic findings) as classi- therapy. fied by the International Encephalitis Consortium. The

procedures (spinal fusion, epidural catheter placement) or Acute Flaccid Myelitis paraspinal injection. Patients usually develop localized pain Acute flaccid myelitis, first reported in 2014, presents as acute- at the site of infection that later radiates down the spine. onset limb weakness, often preceded by respiratory illness or MRI is the imaging modality of choice to identify location fever within the previous 4 weeks. It occurs most often in the and extent of the abscess. All patients should undergo a pediatric population but has been reported in adults. Several baseline laboratory evaluation, including erythrocyte sedi- neuroinvasive enteroviruses have been implicated, including mentation rate and C-reactive protein. Blood cultures EV-A71 and EV-D68. Outbreaks have occurred every 2 years should be obtained before starting antibiotics. Treatment (late summer and early fall) since 2074, and intensive surveil- should be at least 6 weeks of effective antimicrobial therapy. lance is ongoing in the United States. Acute flaccid myelitis can Surgical drainage is indicated in patients with neurologic progress rapidly and may be complicated by respiratory fail- symptoms or signs (lower extremity weakness, numbness, ure, so all patients should be hospitalized initially for close bladder and bowel dysfunction). Follow-up MRI is not indi- monitoring. The CDC has developed interim recommenda- cated unless the patient has persistent elevation of inflam tions for management; however, no evidence has shown any matory markers, lack of clinical response, or new neuro- current therapies affect outcomes. logic symptoms or signs. Tuberculosis (Pott disease) and brucellosis should be considered in patients with negative culture results and appropriate travel history and risk Encephalitis factors. Encephalitis is inflammation of the brain parenchyma. t(tY Ioll{T Probable or conflrmed encephalitis is defined by the presence . MRI is the imaging modality of choice to identify loca- of one major (altered consciousness for more than 24 hours) and at least three minor criteria (fever, new-onset seizure, tion and extent of a spinal epidural abscess, and blood new-onset focal neurologic findings, CSF pleocytosis, and cultures should be obtained before starting antibiotic abnormal MRI or electroencephalographic findings) as classi- therapy. fied by the International Encephalitis Consortium. The 6

Central Nervous System lnfections causative agent is unknown in 37'X, to 70% of infections, encephalitis, Powassan, and La Crosse viruses. WNV is the depending if viral PCR and arboviral serologies are performed most common cause of epidemic viral encephalitis in the and autoimmune causes are investigated. The most common United States; meningitis, acute flaccid paralysis (similar to known causes are viral (herpes simplex virus types 1 and 6, poliomyelitis), neuropathy, and retinopathy can also occur. varicella-zoster virus IVZV), and West Nile virus [WNV]) and Older patients and those who have undergone transplantation autoimmune diseases. or are immunosuppressed have a higher risk of death. WNV affects the thalamus and the basal ganglia; patients present Viral Encephalitis with facial or arm tremors, parkinsonism, and myoclonus. Herpes Simplex Encephalitis Hypodense lesions or enhancements may be seen in the thala- HSV 1 is the most common cause of sporadic encephalitis in mus, basal ganglia, and midbrain on MRI of the brain. A posi- the United States, requiring prompt identification and tive WNV IgM in the CSF or serum confirms the diagnosis; treatment with intravenous acyclovir. Factors associated treatment is supportive. with an adverse outcome include older age, abnormal HIV encephalitis is the cause of HIV associated dementia Glasgow Coma Scale score, and delay in starting antiviral in later stages of the untreated illness; it can also present as therapy. HSV-1 encephalitis commonly presents with fever, CD8 encephalitis, consisting of perivascular inflammation seizures, altered mental status, and focal neurologic deficits resulting from infiltration of CD8* lymphocytes, which may with unilateral temporal lobe edema, hemorrhage, or occur as part of an immune reconstitution syndrome, in some enhancement on imaging. The CSF formula usually shows cases associated with viral escape (low levels of detectable HIV lymphocytic pleocytosis, an elevated protein level, and a RNA in CSF). normal glucose level. The diagnosis is confirmed by HSV PCR K EY PO I T{TS of the CSF (98% sensitivity, 94% specificity). However, false negative results have been reported; if HSV is suspected, a . Herpes simplex virus type 1 is the most common cause of sporadic encephalitis in the United States, presenting repeat PCR should be obtained within l week while continu- ing acyclovir therapy. Therapy duration for HSV encephalitis with fever, seizures, altered mental status, and focal neurologic deficits; prompt identification and treatment should be 14 to 21 days. Electroencephalography can be help- ful in identifying the degree of cerebral dysfunction and with intravenous acyclovir improves outcomes. specific area of the brain involved and in detecting subclini- o Varicella-zoster virus (VZV) is a treatable form of cal seizure activity. encephalitis and may present without vesicular rash, Human herpesvirus 6 can cause severe limbic encephali so VZV polymerase chain reaction of the cerebrospi- tis (altered consciousness, focal neurologic signs, seizures, nal fluid should be ordered in all patients with psychosis) in bone marrow transplant recipients. Antiviral encephalitis. agents are often used to treat infection in immunocompro- o West Nile virus is the most common cause of epidemic mised patients, although data supporting treatment are viral encephalitis in the United States and occurs limited. Cytomegalovirus can cause encephalitis with peri- between June and October and may present with acute ventricular enhancement on imaging in immunosuppressed flaccid paralysis or parkinsonism. patients (those with AIDS or after transplantation). Diagnosis is by PCR of the CSF for cytomegalovirus, and treatment is parenteral ganciclovir. Cytomegalovirus and Epstein-Barr Autoimmune Encephalitis virus can cause meningoencephalitis in young, immunocom- Autoimmune neurologic diseases can manifest as encepha- petent patients presenting with infectious mononucleosis litis, cerebellitis, dystonia, status epilepticus, cranial syndromes. neuropathies, and myoclonus. Anti-l{-methyl-o-aspartate receptor encephalitis is most common and presents with a Varicella-Zoster Virus Encephalitis subacute onset; it was initially described as a paraneo- VZV is a commonly underdiagnosed, treatable cause of plastic syndrome affecting young women with ovarian encephalitis in adults. VZV can present with vasculopathy teratomas, but it can be associated with other tumors (sex with a stroke, encephalitis, meningitis, radiculopathy, or mye- cord stromal tumors, small cell lung cancer) or occur with- litis. Patients can present without a vesicular rash, so a CSF out a tumor. HSV and VZV encephalitis have been reported VZV PCR should be ordered in all patients with encephalitis. as triggers for subsequent autoimmune encephalitis. Young Treatment with intravenous acyclovir for 10 to 14 days is women (<35 years) often present after viral-like illness recommended. with behavioral changes, headaches, and fever followed by altered mental status, seizures, abnormal movements, and Arboviruses autonomic instability. Treatment includes intravenous Arboviral CNS infections in the United States are most com- glucocorticoids, intravenous immune globulin, tumor monly seen between June and October and include West removal (if present), and, in some cases, plasmapheresis Nile, Eastern and Western equine encephalitis, St. Louis and rituximab.

causative agent is unknown in 37'X, to 70% of infections, encephalitis, Powassan, and La Crosse viruses. WNV is the depending if viral PCR and arboviral serologies are performed most common cause of epidemic viral encephalitis in the and autoimmune causes are investigated. The most common United States; meningitis, acute flaccid paralysis (similar to known causes are viral (herpes simplex virus types 1 and 6, poliomyelitis), neuropathy, and retinopathy can also occur. varicella-zoster virus IVZV), and West Nile virus [WNV]) and Older patients and those who have undergone transplantation autoimmune diseases. or are immunosuppressed have a higher risk of death. WNV affects the thalamus and the basal ganglia; patients present Viral Encephalitis with facial or arm tremors, parkinsonism, and myoclonus. Herpes Simplex Encephalitis Hypodense lesions or enhancements may be seen in the thala- HSV 1 is the most common cause of sporadic encephalitis in mus, basal ganglia, and midbrain on MRI of the brain. A posi- the United States, requiring prompt identification and tive WNV IgM in the CSF or serum confirms the diagnosis; treatment with intravenous acyclovir. Factors associated treatment is supportive. with an adverse outcome include older age, abnormal HIV encephalitis is the cause of HIV associated dementia Glasgow Coma Scale score, and delay in starting antiviral in later stages of the untreated illness; it can also present as therapy. HSV-1 encephalitis commonly presents with fever, CD8 encephalitis, consisting of perivascular inflammation seizures, altered mental status, and focal neurologic deficits resulting from infiltration of CD8* lymphocytes, which may with unilateral temporal lobe edema, hemorrhage, or occur as part of an immune reconstitution syndrome, in some enhancement on imaging. The CSF formula usually shows cases associated with viral escape (low levels of detectable HIV lymphocytic pleocytosis, an elevated protein level, and a RNA in CSF). normal glucose level. The diagnosis is confirmed by HSV PCR K EY PO I T{TS of the CSF (98% sensitivity, 94% specificity). However, false negative results have been reported; if HSV is suspected, a . Herpes simplex virus type 1 is the most common cause of sporadic encephalitis in the United States, presenting repeat PCR should be obtained within l week while continu- ing acyclovir therapy. Therapy duration for HSV encephalitis with fever, seizures, altered mental status, and focal neurologic deficits; prompt identification and treatment should be 14 to 21 days. Electroencephalography can be help- ful in identifying the degree of cerebral dysfunction and with intravenous acyclovir improves outcomes. specific area of the brain involved and in detecting subclini- o Varicella-zoster virus (VZV) is a treatable form of cal seizure activity. encephalitis and may present without vesicular rash, Human herpesvirus 6 can cause severe limbic encephali so VZV polymerase chain reaction of the cerebrospi- tis (altered consciousness, focal neurologic signs, seizures, nal fluid should be ordered in all patients with psychosis) in bone marrow transplant recipients. Antiviral encephalitis. agents are often used to treat infection in immunocompro- o West Nile virus is the most common cause of epidemic mised patients, although data supporting treatment are viral encephalitis in the United States and occurs limited. Cytomegalovirus can cause encephalitis with peri- between June and October and may present with acute ventricular enhancement on imaging in immunosuppressed flaccid paralysis or parkinsonism. patients (those with AIDS or after transplantation). Diagnosis is by PCR of the CSF for cytomegalovirus, and treatment is parenteral ganciclovir. Cytomegalovirus and Epstein-Barr Autoimmune Encephalitis virus can cause meningoencephalitis in young, immunocom- Autoimmune neurologic diseases can manifest as encepha- petent patients presenting with infectious mononucleosis litis, cerebellitis, dystonia, status epilepticus, cranial syndromes. neuropathies, and myoclonus. Anti-l{-methyl-o-aspartate receptor encephalitis is most common and presents with a Varicella-Zoster Virus Encephalitis subacute onset; it was initially described as a paraneo- VZV is a commonly underdiagnosed, treatable cause of plastic syndrome affecting young women with ovarian encephalitis in adults. VZV can present with vasculopathy teratomas, but it can be associated with other tumors (sex with a stroke, encephalitis, meningitis, radiculopathy, or mye- cord stromal tumors, small cell lung cancer) or occur with- litis. Patients can present without a vesicular rash, so a CSF out a tumor. HSV and VZV encephalitis have been reported VZV PCR should be ordered in all patients with encephalitis. as triggers for subsequent autoimmune encephalitis. Young Treatment with intravenous acyclovir for 10 to 14 days is women (<35 years) often present after viral-like illness recommended. with behavioral changes, headaches, and fever followed by altered mental status, seizures, abnormal movements, and Arboviruses autonomic instability. Treatment includes intravenous Arboviral CNS infections in the United States are most com- glucocorticoids, intravenous immune globulin, tumor monly seen between June and October and include West removal (if present), and, in some cases, plasmapheresis Nile, Eastern and Western equine encephalitis, St. Louis and rituximab. 7