CNS infections

Question 1

Primary infections of the CNS =

Answer 1

meningitis, encephalitis, brain abscess

Question 2

Meningitis classification

Answer 2

• Acute pyogenic = usually bacterial, presents suddenly and severely
• Aseptic = usually viral, lymphocytes in CSF –
• Chronic = signs and symptoms for weeks-months – mycobacterium TB (tubercular meningitis),

Question 3

How does meningitis enter the CNS

Answer 3

• Haematogenous spread - arterial but can be venous
• Direct implantation - most often trauma related but can be iatrogenic or congenital – meningomyelocele
• Local extension - most often from mastoid, frontal sinuses, infected tooth
• Along peripheral nerves – usually viruses

Question 4

Clinical features of meningitis

Answer 4

• Headache, irritable, neck stiffness, photophobia, fever, varying level of consciousness, rash

Question 5

Acute bacterial meningitis

Answer 5

• Diagnosis = Blood cultures, lumbar puncture

- Dexamethasone shown to decrease morbidity and mortality in s.pneumoniae but not n.meningitidis

Question 6

Viral meningitis

Answer 6

• Primarily affects children and young adults
• May start as respiratory or intestinal infection then viraemia
• CSF shows raised lymphocyte count (50-200/cu mm); protein and sugar usually normal
• Full recovery expected

Question 7

Tubercular meningitis

Answer 7

• Insidious onset
• High frequency of complications, cranial nerve palsies
• CSF shows predominantly lymphocytic response but polymorphs also present
• High protein, low/absent sugar

Question 8

Encephalitis definition

Answer 8

• Encephalitis is an acute inflammatory process affecting the brain parenchyma
• Viral infection is the most common and important cause, with over 100 viruses implicated worldwide

Question 9

Encephalitis symptoms

Answer 9

• Fever
• Headache
• Behavioural changes
• Altered level of consciousness
• Focal neurologic deficits
• Seizures

Question 10

Encephalitis causes

Answer 10

• Herpes viruses, adenovirus, influenza, enteroviruses, MMR, rabies
• Arboviruses = Japanese encephalitis

Question 11

Herpes encephalitis

Answer 11

• Focal signs and epilepsy features
• Acute infection or more commonly reactivation of latent infection
• treatment urgently needed with Aciclovir
• Causes severe haemorrhagic encephalitis affecting temporal lobe

Question 12

Rabies

Answer 12

• Acute, progressive viral encephalitis
• Highest case fatality of any infectious disease
• get it from animals (dogs)
• Virus enters nerve endings and advances toward the ganglia, spinal cord and brain
• Infection cycle completed when virus replicates in the salivary glands

Question 13

Neurosyphilis

Answer 13

- CNS invasion in 30-40% of syphilis patients
Features:
- Acute meningitis
- General paresis
- Tabes dorsalis
- Diagnosis by blood & CSF serology

Question 14

Rabies clinical phases

Answer 14

• Prodromal phase – fever, nausea, vomiting, tingling sensations at site of wound
• Furious phase – agitation, disorientation, seizures, twitching, hydrophobia
• Dumb phase – paralyzed, disoriented, stuporous
• Progress to coma phase, resulting in death

Question 15

Brain Abscess definition

Answer 15

Focal suppurative process within the brain parenchyma

Question 16

Brain Abscess spread

Answer 16

• Direct spread (ear, sinus)

- Haematogenous spread

Question 17

Brain Abscess aetiology

Answer 17

• Brain abscesses are often mixed (polymicrobial)
• Streptococci (60-70 %) e.g. Streptococcus “milleri”
• Staphylococcus aureus (10-15 percent) most common pathogen in abscesses after trauma/surgery

Question 18

Brain Abscess presentation

Answer 18

o Headache
o Focal neurological deficit (30-50%)
o Fever (<50%)
o Nausea, vomiting
o Seizures
o Neck stiffness
o Papilloedema

Question 19

Brain Abscess management

Answer 19

• Drainage is treatment of choice but small abscesses can be treated with antibiotics alone