Infectious Diseases in Critical Care Medicine

withL. monocytogenesmeningitis, for example, but the organism is virtually always culturable
from the CSF. With ABM due to the meningococcus, no organisms may be seen on CSF Gram
stain, even in the presence of overwhelming infection due to autolysis by the organism. The CSF
may appear turbid or cloudy due to the abundance of WBCs present. Organisms may not be
visible on the CSF Gram stain, but culture is invariably positive forNeisseria meningitidis.The
typical purulent profile of ABM may also be present in patients with early tuberculous or fungal
meningitis, but more typically present as subacute/chronic meningitis (1,8,27).

Table 9 Diagnostic Approach in Compromised Hosts with Symptoms/Signs of Central Nervous System Infection

Syndrome presentation Diagnostic procedures Comments

.Meningeal signs LP with CSF:
WBC cell count/differential

Determine host defense defect to

predict most likely CNS pathogens

RBC count

Glucose/protein Lactic acid

Cytology

Bacterial signs/culture

AFB fungal smears/culture

Rule out mimics of meningitis

Empiric therapy is based on

cerebrospinal fluid findings

.Encephalitis/
encephalopathy or mass
lesion

Head CT/MRI:

To rule out cerebritis

To rule out mass lesions

To rule out hydrocephalus

To rule out CNS hemorrhage

Determine host defense defect to

predict most likely CNS pathogens

Rule out noninfectious causes by

history/physical exam, and CT/

MRI appearance

LP if papilledema not present:

WBC cell count/differential

Glucose/protein/RBCs

Lactic acid

Cytology

Bacterial strains/culture

AFB fungal smears/culture

Specific therapy based on tissue

diagnosis, or empiric therapy for

the most likely diagnostic

possibility

Abbreviations: CNS, central nervous system; CSF, cerebrospinal fluid; MRI, magnetic resonance imaging; CT,
computed tomography; AFB, acid-fast bacilli; LP, lumbar puncture.

Table 8 CNS Pathogens and Disorders Associated with Impaired T-Lymphocyte/Macrophage–Mediated
Cellular Immunity

.Disorders associated with impaired T-lymphocyte/macrophage-mediated cellular immunity
HIV/AIDS
Lymphoreticular malignancies
Hodgkin’s lymphoma
Chronic immunosuppressive therapy
Organ transplantation (bone marrow, renal, cardiac, pancreatic, hepatic, etc.)
Chronic corticosteroid therapy
Collagen vascular diseases
Systemic vasculitis
Chronic renal failure
Rheumatoid ailments
CMV

CNS pathogens associated with impaired T-lymphocyte/macrophage-mediated cellular immunity

Common Uncommon Rare

Listeria M. tuberculosis (TB) PML
Nocardia Brucellosis Strongyloides stercoralis
Cryptococcus neoformans Aspergillus Toxicara canis
CMV Mucor Pneumocystis (carinii) jiroveci (PCP)
HSV Pseudallescheria boydii
VZV
Toxoplasma gondii

Abbreviations: CNS, central nervous system; CMV, cytomegalovirus; VZV, varicella zoster virus; HSV, herpes
simplex virus; PML, progressive multifocal leukoencephalopahy.

144 Cunha and Smith