Central Nervous System Infections

Overview

CNS infections carry a high mortality if untreated or improperly treated. It is important to recognize and treat differently neonates, young people, adults, old people, and immunocompromised since different organisms affect these different populations.

Infections of the CNS include:

• Symptom triad of CNS infections
  • Fever
  • Headache
  • Altered mental status

Meningitis

Meningitis is infection and inflammation of the meningeal linings. It is important to start IV empiric therapy (ideally treatment should be started as soon as CSF analysis results are back). The #1 cause of meningitis is Streptococcus pneumoniae. Viral meningitis is usually self-limited.

Causes of meningitis according to population

• Risk factors for community acquired meningitis
  • Homelessness
  • Living in group settings e.g. dorms, barracks
  • Asplenia
  • Diabetes
• Other risk factors
  • Sinusitis
  • Mastoiditis
  • Otitis
  • Endocarditis
  • Penetrating head trauma
  • Basilar skull fracture
  • Recent neurosurgical procedure
  • Alcoholism
  • HIV
• Signs and symptoms
  • Fever
  • Headache
  • “Stiff neck”/ Nuchal rigidity
  • Vomiting (non-specific)
  • Photophobia
    • Kernig sign (pain on hip flex/knee extension)
    • Brudzinski sign (involuntary leg lifting on neck flexion)
  • Rash (Particularly in young people. Does not fade when a glass is pressed against it. Do a thorough dermatological exam → if present start 3rd gen cephalosporin)
• Investigations
  • Head CT: best first step before lumbar puncture; especially in patients with elevated intracranial pressure or risk of intracranial pressure (immunocompromised)
  • LP with CSF analysis: Technically the best first step in patients without signs of elevated intracranial pressure
  • CSF culture: most accurate test, does not play a role in treatment
• Treatment
  • IV empiric therapy
    • IV Vancomycin AND 3rd gen cephalosporin (Cefotaxime, Ceftriaxone) – to cover Strep and Neisseria + IV Steroids (Dexamethasone)
    ***Vancomycin has better meningeal penetration
  • Other options
    • IV Ampicillin: if patient is <2y, >60y, or immunocompromised to cover for Listeria
    • Amphotericin B: Cryptococcal meningitis
    • Quadruple therapy (INH, Rifampin, Pyrimethamine, Ethambutol): TB meningitis
    • High dose Penicillin – Syphilitic meningitis
  • Seizure precaution (if the patient is severely symptomatic)
  • Follow up for possible neurological sequelae (Seizure disorders, SNHL) particularly in children
• Complications
  • Permanent neurological deficit (commonly sensorineural hearing loss)
  • Seizures
  • Cognitive impairment
  • Secondary intracranial infection e.g. empyema
  • Waterhouse-Freidrischen syndrome
• Waterhouse-Freidrichsen syndrome
  • A very feared complication of meningococcemia resulting in bilateral hemorrhage into the adrenal glands causing severe acute adrenal insufficiency
  • Symptoms
    • Hypotension
    • Hyponatremia
    • Hyperkalemia
    • Thrombocytopenia
    • Other symptoms of sepsis
  • Treatment
    • 3rd gen cephalosporin (Cefotaxime, Ceftriaxone)

CSF analysis: 3 major parameters are read in a CSF analysis – Protein, glucose, and cell count

Encephalitis

Encephalitis is an infection and inflammation of the brain parenchyma resulting in neurological dysfunction. Patients may have meningeal symptoms since infection generally extends to or from the meningeal space (commonly early in the disease presentation). IV empiric therapy should be commenced immediately if suspected.

Common causes of encephalitis are viruses (HSV, CMV, VZV, West Nile)

• Signs and symptoms
  • Fever
  • Headache
  • Nausea
  • Vomiting
  • Meningism (nuchal rigidity, positive Kernig, positive Brudzinski)
  • Confusion
  • Behavioral disturbances
  • Altered Mental Status
  • Seizures
• Investigations
  • Head CT: best first diagnostic step; Temporal lobe enhancement can be seen in CT (Herpes encephalitis)
  • LP with CSF analysis: differentiate encephalitis from meningitis, will show a viral picture (high protein, high lymphocytes, normal glucose)
• Treatment
  • IV empiric therapy
    • Acyclovir + Dexamethasone
    • Ganciclovir or Foscarnet for suspected CMV encephalitis (HIV/AIDS, immunocompromised patient)
  • Seizure prophylaxis (in pts with raised ICP)
    • Scheduled Benzos (Lorazepam, Diazepam)
    • Diuretic (Furosemide, Mannitol) to lower ICP
  • Prophylaxis for treatment of close contacts
    • Ciprofloxacin OR Rifampin

Cerebral abscess

A cerebral abscess is a focal infection of brain parenchyma (a big pus tumour). It presents with focal neurological deficits and signs of raised intracranial pressure. Empiric therapy should not be delayed, however, getting a sample for culture and sensitivity to know the bacteria present is appropriate.

Organisms are commonly introduced via a contiguous spread. Streptococcus and staphylococcus species are the most common bacteria responsible though most infections are polymicrobial.

Causative organisms

• Risk factors in adults
  • Lung infection
  • Dental abscess
  • Sinusitis
  • Otitis
  • Mastoiditis
  • Endocarditis
• Risk factors in children
  • Cyanotic heart disease
  • Pulmonary arteriovenous malformation
• Predisposing factors
  • Diabetes
  • Chronic steroid use
  • Sarcoidosis
  • HIV
  • Immunosuppression
  • Organ transplant
  • Recent cranial or dental procedure
• Signs and symptoms
  • Fever
  • Headache
  • Nausea
  • Vomiting
  • Focal neurological deficits (weakness, ataxia, hemiparesis, dyslexia, etc.)
  • Papilledema
  • Seizures
• Investigations
  • Head CT: The best first diagnostic step to locate the abscess. Will clearly show the abscess
    • Single ring-enhancing region typically at the grey-white matter junction and watershed areas
    • Multiple foci of abscesses in toxoplasmosis
  • MRI:
    • Ring enhancement
    • Hyperintense on T2
  • Aspiration biopsy: Most accurate test; will show us what causative organism
  • Labs: CBC, ESR, CRP
• Differentials for a solitary ring-enhancing lesion (MAGICAL DR)
  • Metastasis
  • Abscess
  • Glioblastoma
  • Infarct
  • Contusion
  • Aneurysm
  • Lymphoma
  • Demyelinating disease
  • Radiation necrosis
• Treatment
  • Empiric antibiotics while preparing for surgery. A minimum of 6 weeks antibiotics is given.
    • IV beta-lactam (Penicillin, Nafcillin) – cover streptococci
    • IV Clindamycin OR Metronidazole – cover anaerobes
    • IV 3rd gen cephalosporin (Ceftriaxone, Cefotaxime) – cover gram negatives
  • If the patient has AIDS (presumed toxoplasmosis)
    • Pyrimethamine AND Sulfadiazine (Surgery not necessary, will respond in 10-14 days)
    • If they do not respond, exclude abscess and consider a CNS lymphoma
  • Surgical drainage if the abscess if > 2.5 cm, mass effect, signs of raised ICP or clinical deterioration
  • Antiepileptic agents in the acute and peri-operative period (abscesses commonly cause seizures, especially those in the frontal and temporal lobe)

Empyema

An empyema is a collection of purulent material, commonly in the subdural space. It can also occur in the epidural space. They were historically referred to as abscesses but the term empyema is preferred now. The clinical presentation is similar to meningitis. A subdural empyema is a surgical emergency. Antibiotics alone won’t control infection.

• Risk factors
  • ENT infection (sinusitis, otitis, mastoiditis)
  • Skull trauma
  • Neurosurgical procedure
  • Meningitis
• Signs and symptoms
  • Fever
  • Headache
  • Vomiting
  • Altered mental status
  • Seizure
• Investigations
  • CT or MRI: diagnostic method of choice. It may be difficult to locate a collection in the posterior fossa on CT.
    • Crescent or elliptical collection of hypo intensity on T1 MRI
    • Mass effect or midline shift may be present
  • Aspirate for culture and sensitivity
• Treatment
  • IV broad spectrum antibiotics for at least 3 – 4 weeks
  • Surgical drainage
  • Anti-epileptic medication for seizure prophylaxis
  • Craniectomy and extension of duration of antibiotics if there is adjacent osteomyelitis

Measuring Opening Pressure during Lumbar Puncture