Infectious Diseases of the Nervous System

Cerebrospinal Fluid

• 1.

  What is the normal composition of cerebrospinal fluid (CSF)?

  See Table 25-1 .

  Table 25-1

  Normal Composition of Cerebrospinal Fluid (CSF)

  From Irani DN: Cerebrospinal Fluid in Clinical Practice . Philadelphia, Elsevier, 2009.

  Opening Pressure	WBC	RBC	Protein	Glucose
  8-15 mm Hg or 100-180 mm H 2 O	0-5/mm 3	0/mm 3	15-45 mg/dL	45-80 mg/dL

  WBC, White blood cells; RBC, red blood cells.

• 2.

  List common contraindications to performing a lumbar puncture.

  • Infection: cellulitis, abscess

  • Space-occupying lesion

  • Uncal, central, transtentorial, or cerebellar herniation

  • Coagulopathy: thrombocytopenia, liver failure, anticoagulant use

• 3.

  List the major complications of a lumbar puncture.

  • Headache

  • CSF leak

  • Infection

  • Bleeding

  • Rarely herniation

• 4.

  Describe the basic technique involved in performing a lumbar puncture.

  • Obtain computed tomography/magnetic resonance imaging (CT/MRI) brain indicated for patients with papilledema, altered mental status, focal neurologic deficit, new-onset seizure, or immunocompromised state.

  • Ensure that platelet count is >50,000, and international normalized ratio is <1.5.

  • Place patient in lateral decubitus position, with knees and neck flexed.

  • Ensure patient’s back is as close to edge of bed as possible.

  • Palpate top of iliac crest and then place thumb of same hand in the interspace forming a vertical line with the top of the iliac crest.

  • The identified location indicates the L3-L4 space. The needle can be placed into the L3-L4, L4-L5, or L5-S1 interspaces.

  • Avoid L2-L3 interspace and higher since the conus medullaris terminates at L1-L2.

  • Insert needle, with the bevel parallel to longitudinal fibers of the supraspinous ligament.

  • Advance needle, and a “pop” should be felt, indicating the piercing of the needle through the supraspinous ligament. Advance needle into the subarachnoid space.

• 5.

  Describe the typical composition of CSF by type of infectious agent.

  See Table 25-2 .

  Table 25-2

  Typical Findings in Cerebrospinal Fluid (CSF) by Type of Infection

  	Opening Pressure	WBC	Protein	Glucose
  Bacterial	Elevated	>1000/mm 3 PMN predominance	>120 mg/dL	<30 mg/dL
  Viral	Normal	<100/mm 3 Lymphocytic predominance	Normal-elevated	Normal
  Fungal	Normal-slightly elevated	20-500/mm 3 Lymphocytic predominance	Elevated	Decreased
  Tuberculosis	Elevated	10-500/mm 3 Lymphocytic predominance	100-500 mg/dL	35-40 mg/dL
  Syphilis	Increased	Mononuclear predominance	Elevated	Normal
  Lyme disease	Normal	Lymphocytic predominance	Increased	Normal

  WBC, White blood cells; PMN, polymorphonuclear leukocyte.

Roos KL (ed): Principles of neurologic infectious diseases: principles and practice . New York: McGraw-Hill, 2004.

Bacterial Meningitis

• 6.

  Name the common pathogens causing bacterial meningitis by population group, and indicate the typical empiric therapy for these bacterial pathogens.

  See Table 25-3 .

  Table 25-3

  Bacterial Meningitis by Population Type and Appropriate Therapy

  From Roos KL (Editor): Principles of Neurologic Infectious Diseases: Principles and Practice . New York, McGraw-Hill, 2004.

  Population Group	Common Pathogens	Empiric Therapy
  Newborns	Gram negative: Escherichia coli , Klebsiella , Enterobacter , Proteus group B streptococci: Streptococcus agalactiae	Cefotaxime + Ampicillin
  Infants and children	Neisseria meningitidis , Streptococcus pneumoniae , Hemophilus influenzae	Ceftriaxone or cefotaxime plus vancomycin
  Healthy, immunocompetent	N. meningitidis , S. pneumoniae , Listeria monocytogenes	Third/fourth-generation cephalosporin plus ampicillin plus vancomycin
  Nosocomial/postneurosurgical	Gram-negative Enterobacteriaceae, Pseudomonas aeruginosa , staphylococci	Meropenem plus vancomycin
  Ventriculitis	Staphylococcus epidermidis , Staphylococcus aureus , gram-negative Enterobacteriaceae, P. aeruginosa	Meropenem plus vancomycin
  Elderly	L. monocytogenes , gram-negative Enterobacteriaceae, P. aeruginosa , pneumococci	Third/fourth-generation cephalosporin plus ampicillin plus vancomycin

• 7.

  When is chemoprophylaxis for meningococcal meningitis appropriate, and what antimicrobials can be used?

  Every person sleeping in the same house and those contacts engaging in saliva exchanging oropharyngeal secretions should undergo chemoprophylaxis.

  • Rifampin: adults, infants

  • Ciprofloxacin: adults

  • Ceftriaxone: adults, children

• 8.

  What is the role of adjunctive corticosteroids in the treatment of bacterial meningitis?

  The benefits of intravenous corticosteroids in bacterial meningitis come from the reduction of the inflammatory process that leads to significant morbidity and mortality. Corticosteroids are thought to help decrease intracranial pressure (ICP) and reduce brain edema and meningeal inflammation. In children, corticosteroids have been shown to reduce the incidence of sensorineural hearing loss. Studies in adults showed protection in patients with Streptococcus pneumoniae meningitis. Treatment showed association with significant reduction in unfavorable outcome and mortality. The dosing regimen is dexamethasone 4 mg intravenously every 6 hours for 4 days with the first dose given 30 minutes prior to the first dose of antibiotics. If the CSF cultures indicate the pathogen is not S. pneumoniae , the dexamethasone may be discontinued.

• 9.

  Describe the pathogenesis, common clinical findings, diagnostic approach, neuroimaging findings, and complications of bacterial meningitis.

  See Table 25-4 .

  Table 25-4

  Bacterial Meningitis

  Data from Roos KL: Meningitis: 100 Maxims. London, Arnold, 1996

  Pathogenesis	Bacteria enter subarachnoid space → replication and autolysis → release of bacterial components in CSF → release of proinflammatory host factors
  Clinical findings	Stiff neck, headache, fever, photophobia, malaise, vomiting, lethargy → deterioration of level of consciousness
  Diagnosis	Lumbar puncture: elevated opening pressure, polymorphonuclear leukocytic pleocytosis, elevated protein, low glucose, and elevated lactate in postneurosurgical patients, gram-stained smear, CSF culture Blood cultures, CRP/ESR
  CT/MRI findings	Cerebral edema, hydrocephalus, ventriculitis, vasculitis, septic embolism, sinus venous thrombus causing infarction, intracranial free air due to dural leak
  Complications	Death with highest mortality in pneumococcal and Listeria meningitis Sensorineural hearing loss Hemiparesis, epileptic seizures, hemianopia, ataxia, cranial nerve palsies

  CSF , Cerebrospinal fluid; CRP , C-reactive protein; ESR , sedimentation rate.