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 can occur

Answer 2

• breach of BBB (tightly packed endothelial cells supported by basement membrane) by infectious agent = en encephalitis
• breach of blood-CSF barrier (at arachnoid membrane and ventricles) by infectious agent = meningitis
• direct spread: sinuses, otitis media, skull fracture

Question 3

Describe the main mechanisms of barrier breach

Answer 3

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

Question 4

What are the main causes of meningitis?

Answer 4

Bacteria: N. meningiditis, H. influenzae, S. pneumoniae

Viral: enteroviruses, HSV1/2

Fungal and protozoal causes

Question 5

Describe the features of N. meningiditis

Answer 5

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

Question 6

Describe the features of H. influenzae

Answer 6

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

Question 7

Describe the features of S. pneumoniae

Answer 7

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

Question 8

What are the clinical features of meningitis in children?

Answer 8

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

Question 9

What are the classic clinical features of meningitis?

Answer 9

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

Question 10

Describe the diagnostic tests for meningitis

Answer 10

Bloods:

• biochem: U and Es, CRP, lactate and glucose
• haem: FBC and clotting
• microbio: culture, meningococcal and pneumococcal PCR, HIV test

CSF:

• biochem: protein and glucose
• microbio: white cell count, gram stain, culture, meningococcal and pneumococcal PCR

Question 11

In what circumstances would you delay doing a lumbar puncture?

Answer 11

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

Question 12

Differentiate the CSF findings of bacterial vs viral meningitis

Answer 12

Bacteria:

• white cell count: big increase
• protein: big increase
• glucose: big decrease
• cloudy (due to increased pressure)

Viral:

• increased white cell count
• increased protein
• decreased glucose

Question 13

What is the treatment of meningitis?

Answer 13

Bacterial

• antibiotics (ceftriaxone)
• some types require adjunctive corticosteroid (dexamthosone)

Viral:
- no specific treatment

Question 14

What is the most common cause of encephalitis?

Answer 14

HSV-1 (causes altered cerebration)

Question 15

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

Answer 15

Risk: otitis media, mastoiditis, sinusitis

Causes: oropharyngeal microbiota (eg. S. aureus and bacteroides sp.)

Treatment: antibiotics (ceftriaxone and metronidazole)