Infections of the CNS

Question 1

Define the main CNS infections

Answer 1

Meningitis: inflammation of the meninges (infection/auto-immune/malignancy)

Encephalitis: inflammation of the brain parenchyma

Question 2

Explain how a CNS infection occurs

Answer 2

• breach of BBB by infectious agent causes encephalitis
• breach of blood-CSF barrier by infectious agent causes encephalitis
• direct spread (sinuses/otitis media/skull fracture)

Question 3

Describe the mechanism of barrier breach

Answer 3

• pathogen growing across and infecting cells compromising the barrier
• passive transfer in intracellular vacuole
• carriage across in infected WBC

Question 4

What are the main causes of meningitis?

Answer 4

Bacteria: N. meningitidis, H. influenzae, S. pneumoniae
Viral: enteroviruses, HSV1/2
Fungal
Protozoa

Question 5

Describe features of N. meningitidis

Answer 5

• gram negative diplococci
• part of normal microbiota in nasopharynx
• droplet/direct contact spread
• 5 pathogenic serogroups: A, B, C, W135, Y

Question 6

Describe features of H. influenzae

Answer 6

• gram negative coccobacilli
• 6 pathogenic serogroups: a-f
• type b is most virulent
• can cause airway exacerbations
• vaccine preventable

Question 7

Describe features of S. pneumoniae

Answer 7

• gram positive diplococci
• part of normal microbiota in nasopharynx
• common in people with specific risk factors (old/diabetic/asplenic etc.)
• 90+ pathogenic serogroups
• also causes pneumonia, otitis media, bloodstream infections
• vaccine preventable

Question 8

What are the clinical features of meningitis?

Answer 8

Babies and small children:

• tense/bulging soft spot on head (increased ICP)
• refusing to feed
• irritable when picked up with a high-pitched or moaning cry
• stiff with jerky movements of floppy and lifeless

Classic signs:

• photophobia
• neck stiffness
• rash
• severe headache
• fever and or vomiting
• seizures

Question 9

Describe the diagnostic tests for bacterial meningitis

Answer 9

Bloods:

• biochemistry: Us and Es, CRP, lactate and glucose
• haematology: FBC and clotting
• microbiology: blood culture, meningococcal and pneumococcal PCR, HIV test

CSF:

• biochemistry: protein and glucose
• microbiology: white cell count, gram stain, bacterial culture, meningococcal and pneumococcal PCR, viral PCR

Question 10

When would you delay taking a CSF sample?

Answer 10

• severe sepsis
• really high ICP
• risk of bleeding
• sign of mass brain lesion

Question 11

Differentiate bacterial and viral meningitis

Answer 11

Bacterial is more severe
Viral is more common

CSF findings:
Bacterial: big increase in WBC (neutrophils) and protein, big decrease in glucose and is cloudy due to increase in pressure

Viral: increase in WBC (lymphocytes) and protein, decrease in glucose

Question 12

What is the treatment for meningitis?

Answer 12

Bacterial: antibiotics (ceftriaxone), some types require adjunctive corticosteroid (dexamethasone)

Viral: no specific treatment

Question 13

What is the causes of encephalitis?

Answer 13

Most common cause is HSV-1

* causes altered cerebration

Question 14

What is the risk factors, causes and treatment of brain abscesses?

Answer 14

Risk factors: otitis media, mastoiditis, sinusitis
Causes: oropharyngeal micrbiota (eg. S. aureus and bacteroides sp.)
Treatment: antibiotics (ceftriaxone and metronidazole)

Question 15

List some spongiform encephalopathies

Answer 15

Human:

• Creutzfeldt-Jakob Disease (CJD)
• variant CJD

Animal:

• bovine spongiform encephalopathy (BSE)
• kuru
• scrapie