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Infections of the Central Nervous System

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1 Infections of the Central Nervous System
MLAB 2434 – Microbiology Keri Brophy-Martinez

2 General Concepts Infections of the CNS are of critical concern and positive laboratory findings are “critical values” Infections may be caused by bacteria, fungi, viruses or parasites

3 Anatomy of CNS Brain, Spinal Cord and Cranial Nerves Meninges
Dura mater Pia arachnoid Pia mater Subarachnoid space between pia arachnoid and pia mater; CSF

4 CSF Unique body fluid produced by filtration and secretion from specialized capillary tufts of the four ventricles of the brain Circulates around brain and spinal cord under pressure Serves as cushion for brain and spinal cord

5 CSF Characteristics CSF is a clear and colorless sterile fluid
Adults Protein mg/dL Glucose mg/dL WBC 0-5 mm3 Newborns Higher levels of protein & glucose Infections indicated by increased cell counts and alterations in protein and glucose

6 CNS Infections Portals of entry for bacteria
Respiratory (most common route of community-acquired infections) Auditory Bloodstream Neural routes Contiguous sites

7 Types of CNS Infections
Meningitis Also called “leptomeningitis” (pia mater & arachnoid) Inflammation around blood vessels within the subarachnoid space Classifications Acute Chronic Aseptic

8 Bacterial CNS Infections
Acute Bacterial Meningitis Peaks in winter & early spring Symptoms include photophobia, headache, nausea, vomiting, and stiff neck or Brundzinski sign In infants, only symptoms may be irritability, poor feeding, and restlessness

9 Bacterial CNS Infections (cont’d)
Acute Bacterial Meningitis (cont’d) Infants Group B Strep L. monocytogenes H. influenzae S. pneumoniae E. coli Children N. meningitidis

10 Bacterial CNS Infections (cont’d)
Acute Bacterial Meningitis (cont’d) Adolescents N. meningitidis S. pneumoniae Adults Elderly Gram-negative bacilli

11 Bacterial CNS Infections (cont’d)
Acute Bacterial Meningitis (cont’d) Lab findings Leukocytosis with left shift and toxic changes, such as toxic granulation & Dohle bodies Increased CSF protein Decreased CSF glucose Increased intracranial pressure

12 Types of CNS Infections (cont’d)
“Aseptic Meningitis” CSF shows predominance of lymphocytes with no organisms on direct examination Commonly caused by viruses Enterovirus Arbovirus Mumps virus Herpes Simplex Virus

13 Types of CNS Infections (cont’d)
Encephalitis/ Meningoencephalitis Diffuse inflammation of the cerebral cortex Observe mental changes or neurologic signs Common in viral infections

14 Types of CNS Infections (cont’d)
Brain Abscesses Areas of tissue destruction containing organisms and inflammatory cells Occur as spread from other body sites or trauma to skull; infecting organism depends on predisposing conditions Non-traumatic abscesses mostly are aerobic and anaerobic streptococci, Staphylococcus aureus, anaerobic GNR

15 Bacterial CNS Infections (cont’d)
Mycobacterial Infection Most commonly M. tuberculosis Enters by respiratory route and spread via bloodstream CSF cells are mostly lymphocytes and monocytes Mycobacteria are few and CSF should be centrifuged to concentrate before culturing/gram staining

16 Bacterial CNS Infections (cont’d)
Spirochetal Infections Lyme Disease Neurosyphilis Viral Infections Enterovirus Arboviruses Herpes Virus Parasitic Infections Toxoplasma gondii Naegleria fowleri Fungal Infections Crytococcus neoformans Candida species

17 Laboratory Diagnosis of CNS Infections
CSF Collection Lumbar puncture in lower back 3 to 4 tubes collected 1st = chemistries 2nd = microbiology 3rd = cell counts 4th = special procedures (if collected) Process ASAP

18 Laboratory Diagnosis of CNS Infections (cont’d)
CSF Analysis Acute Bacterial Meningitis CSF turbid or cloudy WBC increased with predominance of neutrophils Increased CSF protein Decreased CSF glucose Centrifugation concentrates organisms Should be plated on at least BAP, CA and broth; MAC if Gram-negative bacilli are expected Bacterial Antigen Testing Current literature indicates routine bacterial antigen testing is of limited value

19 Laboratory Diagnosis of CNS Infections (cont’d)
CSF Analysis Viral Meningitis Number of lymphocytes increased Diagnosis based on PCR or EIA Fungal Meningitis Gram stain or India ink Culture held for 4-6 weeks

20 Laboratory Diagnosis of CNS Infections (cont’d)
CSF Analysis Tuberculous meningitis Increase in lymphocytes Increase in protein Decrease in glucose AFB stain & culture PCR can be used; however, false positives common

21 Characteristic Findings in Meningitis
Bacterial Fungal Tuberculous Viral Syphilitic Parasitic Organisms seen in CSF See notes None Cell count (leukocytes/mL) ,000 Neutrophils predominate Normal- 500 Lymphocytes predominate 50-500 Normal-200 Lymphocytes/ Eosinophils Protein (mg/dL) Normal- 250 Normal- 150 Frequently normal Usually increased Glucose (mg/dL) <30 Normal- decreased <45 Normal

22 References Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education. Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.

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