Infection of the CNS

Question 1

What is the definition of meningitis?

Answer 1

Inflammation of the meninges which can result in fever, headache and neck stiffness

Question 2

What is encephalitis?

Answer 2

Inflammation of the brain parenchyma

Question 3

What are the possible methods of microbes entering the CNS?

Answer 3

• Via the BBB (breach of which can cause encephalitis).
• If the blood-cerebrospinal spinal fluid (CSF) barrier is breached then it causes meningitis.
• Direct spread from sinus, otitis media or skull fractures

Question 4

What are the common causes of meningitis?

Answer 4

Viral (most common) - Enteroviruses, herpes viruses and paramyxovirus.
Bacteria - Neisseria meningitisis, haemophilus influenzae, streptococcus pneumoniae.
Fungi - Cryptococcus neoformans.
Protozoa - Amoebae, naegleria and acanthamoeba.

Question 5

What are the main causative bacterial organisms for meningitis by different age groups?

Answer 5

• Under 5 year olds is neisseria meningitidis or haemophilus influenzae.
• Young adults is neisseria meningitids,
• Older adults is streptococcus pneumoniae or listeria monocytogenes

Question 6

What are the dangers of neonatal meningitis?

Answer 6

Early onset - Occurs under 7 days, and occurs if the mother is heavily colonised. Premature rupture of membranes and 60% fatality rate.
Late onset - occurs under 3 months, results due to lack of maternal antibodies, or poor hygiene in nursery. 20% fatality rate

Question 7

Describe the features of neisseria meningitidis

Answer 7

Gram negative intracellular diplococci which only infects humans. It is part of the normal microbiota in the nasopharynx. Transmitted by droplet spread or direct contact from carriers. There are 5 pathogenic serogroup strains - A, B, C, W135 and Y. It is vaccine preventable.

Question 8

Describe features of haemophilus influenzae

Answer 8

Gram negative coccobacilli. There are 6 capsular serotypes known to cause disease, most virulent strain is H. influenzae tube b. It is vaccine preventable

Question 9

Describe features of streptococcus pneumoniae

Answer 9

• Gram positive diplococci which is part of the normal microbiota in nasopharynx.
  It can also cause pneumonia, otitis media and bloodstream infections. It is vaccine preventable

Question 10

What are the signs of meningitis in babies/small children?

Answer 10

• Tense or budging soft spot on their head,
• Refusing to feed,
• Irritable when picked up,
• A stiff body with jerky movements of else floppy and lifeless.

Question 11

What are the diagnostic tests?

Answer 11

Blood tests: Biochemistry (U&Es, CRP, lactate and glucose), haematology (FBC and clotting) and microbiology (Blood culture, meningococcal and pneumococcal PCR and HIV test).
CSF tests: Biochemistry (protein and glucose) and Microbiology (WCC, gram staining and bacterial culture, meningococcal and pneumococcal PCR, viral PCR tests, TB, cryptococcal)

Question 12

How do you collect CSF

Answer 12

Via lumbarpuncture. When doing so, you must remember to measure the opening pressure, take matched blood and CSF glucose samples and collect enough fluid.

Question 13

In what situations should you delay doing a lumbar puncture?

Answer 13

Risk of bleeding or focal neurology suggesting a mass lesion.

Question 14

When should you preform CNS imaging?

Answer 14

To exlude mass lesions and/or oedema which might make doing an LP dangerous as in these patients, a reduction in the CSF pressure below the lesion could precipitate herniation of brainstem or cerebellar lesions

Question 15

What is the treatment of bacterial meningitis?

Answer 15

Antibiotics (ceftriaxone) with/without steroids.

Question 16

How can you prevent bacterial meningitis?

Answer 16

Routine vaccination against haemophilus influenzae b, pneumococcus, and meningococcus A, B, C, W and Y. To prevent other neurological infections, ensure polio and tetanus vaccine.

Question 17

What are some features of viral meningitis?

Answer 17

It is much more common than bacterial and identified by PCR of CSF. However no specific treatment and is usually regarded as self-limiting. Can have recurrent or long-term neuropsychiatric consequences.

Question 18

What are the causes, signs and symptoms, investigations and treatments of encephalitis?

Answer 18

Common causes - Herpes simplex virus-1.
Less common causes - other viral infections(VZV, HIV, COVID-19) or other infectious agents.
Signs and symptoms - Altered cerebration. (Confusion, abnormal behavious,) seizures or fever.
Investigations - CSF and temporal lobe changes on MRI scan.
Treatment - high dose aciclovir.

Question 19

What are the pre-disposing factors and causes of brain abscesses

Answer 19

Pre-disposing factors - Otitis media, mastoiditis or sinusitis.
Causes are often oral nasopharyngeal microbiota. eg, aerobic such as s. aureus or anaerobic such as bacteriodes spp.

Question 20

What are the pathophysiology, signs and symptoms, investigations and treatments of brain abscesses?

Answer 20

Pathophysiology - diffuse inflammation which leads to focal lesion and pia mater suppuration.
Symptoms - headaches, focal neurology and seizures.
Investigations - CT/MRI scan +/- invasive sampling.
Treatment - Antibiotics (commonly ceftriaxone and metronidazole.)

Question 21

What are transmissible spongiform encephalopathies?

Answer 21

Rare prion diseases which cause vacuoles and plaques in nervous tissue. They are highly resistant to heat, chemical agents or irradiation. There is no treatment, no vaccine and they are fatal

Question 22

Name some of the transmissible spongiform encephalopathies

Answer 22

Human - CJD or vCJD.

Human - BSE, Kuru and scrapie.

Question 23

explain specifically how barriers are breached?

Answer 23

• Pathogens can grow across and infecting cells which compromising the barrier.
  Passive transfer in intracellular vacuoles or carriage across in infected white blood cells