Bacterial Infections

Approximately 2.5/100,000 (United States) each year

Hematogenous spread most common

• Pneumonia with bacteremia

Other routes

• Direct inoculation (trauma, procedures)

• Invasion (sinusitis, mastoiditis, oral infections)

Birth to 1 month: Streptococcus pneumoniae, E. coli, Listeria monocytogenes

1 month to 29 years: Neisseria meningitidis > Streptococcus pneumoniae

• Haemophilus influenzae (now less common because of vaccine)

30 years to elderly: Streptococcus pneumoniae > Neisseria meningitidis > Listeria monocytogenes

Risk factors

• Liver disease

• Hemoglobinopathies

• Immunodeficiency/debilitated states

Meningococcal meningitis: asymptomatic nasopharyngeal carriers; close personal contact

• Typically late winter epidemics

• Dormitories, barracks, daycare centers

• Sometimes mistaken for flu/pharyngitis

Onset: hours to days

Classic triad—99% to 100% will have at least one :

• Fever

• Altered mental status

• Nuchal rigidity

Less common:

• Photophobia

• Nausea/vomiting

• Seizures

• Focal neuro deficits

Elderly may have atypical presentations

• Nonspecific neurologic findings

• Normal/low temperature

Meningococcal meningitis: classic triad plus rash (may be petechial, purpuric, maculopapular), myalgias, arthritis

Waterhouse-Friderichsen syndrome

• Septicemia

• Shock

• Disseminated intravascular coagulation with purpura

• Bilateral adrenal hemorrhage

CSF

• Leukocytosis (neutrophilia)

• Elevated protein

• Low glucose

Treatment: empiric antibiotics, corticosteroids

Mortality rate

• Nosocomial (35%)

• Community acquired (25%)

Highest mortality

• Pneumococcus

• Listeria

Neurologic sequelae

• Cognitive changes; cranial nerve deficits (hearing loss)

• Seizures

• Hydrocephalus

• Vascular abnormalities

MRI: T1 with contrast: leptomeningeal enhancement

Early: mild edema, vascular congestion

• May be only finding if rapidly fatal; especially meningococcal, pneumococcal disease

Late

• Subarachnoid fibrinopurulent exudate

• Hydrocephalus

• Petechial hemorrhages

Subarachnoid polymorphonuclear neutrophilic infiltration with variable fibrin deposition

Eosinophilic protein stranding

Vessel thrombosis

Ependymitis

Cortical infarcts

GMS (Gomori methenamine silver), AFB (acid-fast bacilli), Gram (bacteria)

Mycobacterial/fungal/viral/chemical meningoencephalitis

Rickettsial infections

Subarachnoid hemorrhage

Drug reaction

Carcinomatosis

Affects 0.3 to 1.3/100,000 people per year, most commonly age 30 to 50 years

Male/female ratio: 2 to 4:1

Extension of local infection in head and neck (most common)

Hematogenous spread

• Pulmonary abscess, bronchiectasis, periodontal disease

Direct inoculation

• Penetrating trauma; iatrogenic

Increased incidence

• Pulmonary arteriovenous malformations

• Immunocompromised patient

• Cyanotic heart disease

• Endocarditis

Sinusitis, otitis media (likely via retrograde thrombophlebitis)

Pathogens

• Anaerobic or microaerophilic streptococci: S. milleri group—most common

• Staphylococci: S. aureus— most common with trauma/craniotomy

• Aerobic gram-negative bacilli (e.g., Proteus, Bacteroides )

• Actinomyces/Nocardia

• Fungi (immunocompromised): Aspergillus, Cryptococcus, Candida, Mucor

• Listeria (associated with glucocorticoid use)

• Mycobacteria or parasites (travelers/immigrants): neurocysticercosis (e.g., Toxoplasma, Entamoeba, Schistosoma japonicum, Paragonimus )

Insidious onset: localized headache (primary symptom); fever (<50% cases)

Increasing perilesional edema may lead to focal neurologic deficits, seizures, deteriorating mental status

CSF findings uncommon unless ventricular involvement

With antibiotics

• Mortality rate ~10% (without ventriculitis)

Neurologic deficits may develop because of associated destruction of CNS tissue

MRI: T1 postcontrast ring-enhancing lesion(s) with significant perilesional edema