Flashcards in W4 - Infections of the CNS - condensed Deck (19):
How do bacteria find their way to the meninges?
Direct spread - Nearby infective focus (paranasal sinusitis, osteomyelitis, otitis media), open skull fracture
Haematogenous (blood borne) - Septicaemia, septic emboli (bacterial endocarditis, bronchestasis, TB)
Iatrogenic - Post lumbar puncture, neurosurgery etc
Write notes on pachymeningitis.
Definition: Inflammation of the dura mater.
- Relatively uncommon compared to leptomeningitis
- Spread: Usually direct spread from from: Mastoiditis, Otitis media, skull fracture
- Main pathogens: G-Bacilli, a/B haemolytic streptococci (from paranasal sinuses), mixed organisms (compound fractures)
- Abscess forms between dura and bones of skull or vertebral column --> suppuration
- Types: Spinal epidural abscess (SEA), intracranial epidural abscess (IEA)
- Suppuration occurring within the subdural space (potential space)
- Complications include: Infection and thrombosis of subdural arteries and veins, CNS infarction
Name two (2) bacteria which are known to cause acute bacterial meningitis.
Any 2 of the following:
- Streptococcus pneumonia
- Neisseria meningiitidis
- Haemophilus influenza
- Liseria monocytogenes
- Streptococcus agalactiae (group B)
- Escherichia coli
- Staphylococcus aureus
Discuss the pathogenesis of acute meningococcal meningitis.
1. Organism resides in nasal cavities, oral cavity and throat of asymptomatic carriers
2. Direct spread via droplet inhalation (eg sneezing) and saliva (eg mouth kissing, sharing drink bottles, sharing cooking utensils etc)
3. Host infected (+/- URTI Ssx) and haematogenous spread
4. Bacteria reaches meninges and suppuration ensues
Discuss the clinical manifestations of meningococcal meningitis.
- Headache (severe)
- Fever (High, >39 deg)
- Neck stiffness and pain (meningeal irritation)
+/- any of the following:
- Brudzinski's sign (forced neck flexion causes reflex hip flexion)
- Kernig's sign (90 deg of hip & knee flexion --> painful knee extension)
Confusion, photophobia, drowsiness and lethargy, fits, high temp, joint pains, neck stiffness, rash, violent/severe HA
Babies and infants:
Fever (hands and feet cold), Refusing feeds or vomiting, High pitched moaning/crying, dislike of being handles, neck retraction with arching of back, blank and staring expression, lethargic and difficult to wake, pale blotchy complexion
How is acute bacterial meningitis diagnosed? How is is treated?
Diagnosed based on the clinical picture (symptoms, and Kernig's and Brudzinski's sign) and a lumbar puncture (including heparin binding levels)
List four (4) complications of acute bacterial meningitis.
Any 4 of the following:
- Disseminated Intravascular Coagulation (DIC) --> skin rash
- Obstructive hydrocephalus
- Cerebral infarction
- Cerebral or subdural abscess
- Waterhouse-Eriderchsen syndrome
- Chronic meningitis
- septic (haemorrhagic) rash
- conjunctival haemorrhage, -
- tissue necrosis
Discuss the epidemiology of acute viral meningitis.
- More common than bacterial meningitis
- Affects >450 people/year in Australia
- Mainly affects children and young adults (90% <30, 70% <20)
- Peak incidence = late summer (mainly due to enteroviruses)
- Differences exist in the ratio female:male and depends on type of virus involved
- 85-95% of all cases of viral meningitis caused by enteroviruses
- Less common causes: Herpes simplex viruses (1&2), varicella-zoster virus, cytomegalovirus, Epstein-Barr virus
Describe the clinical presentation of acute viral meningitis
Acute onset of:
- Headache (severe pre-orbital/frontal, exacerbated by coughing, moving, +/- photophobia)
- Fever (high - 38-40 deg)
- Ssx of meningeal irritation (listlessness, malaise and vomiting, neck pain and stiffness, positive Brudzinski's and Kernig's signs)
Describe the typical "acute viral meningitis" headache.
A severe ("worst they've ever had") throbbing, frontal/retro-orbital headache
Define the term "meningeal irritation". What are the main clinical manifestations?
Irritation of the meninges by bacterial, viral or external lesions.
- Neck stiffness (nuchal rigidity) on flexion
- Headache (severe pre-orbital/frontal)
List and describe the main clinical tests used to detect meningeal irritation. By which mechanisms are these manifestations caused?
Brudzinski’s sign – Pt supine on bed, practitioner rapidly flexes neck. A positive test will see reflex hip & knee (decreases meningeal tension).
Kernig’s sign – Pt supine with knee & hip flexed at 90 degrees. Pt unable to completely extend the leg when hip is flexed. Pt can usually extend the leg completely when the leg is not flexed on the abdomen.
Mechanism: Inflammation of meninges will cause irritation when put under tension. These positions increase meningeal tension (and thus, cause irritation).
Discuss the diagnosis of acute viral meningitis.
CSF examination of Lumbar puncture:
- Pressure: Raised
- Turgid or cloudy appearance (due to presence of pus)
- Elevated neutrophils and proteins
- Normal glucose levels (very low in bacterial meningitis as bacteria use glucose as fuel)
- Negative gram stain and acid-fast bacilli strain (not a bacterial infection)
- Positive viral culture
Typical menigitis Ssx
Clinical findings may also present clues as to identity of virus (parotiditis may implicate mumps virus, skin rash may implicate cox-sackie/echo virus)
Discuss the treatment and prognosis of acute viral meningitis.
Generally very good. In most cases, condition is benign and self-limiting (usually complete resolution in 7-10 days).
Treatment: Antibiotics, rest and hydration
Discuss the pathogenesis of cerebral abscess.
Usually occurs as a complication of other disease (bronchiectasis, frontal sinusitis, trauma, otitis media).
1. Microbes invade CNS tissue, leading to liquefactive necrosis
2. Formation of pus filled cavity
3. Fibrogliosis occurs, forming a hard capsule around the pus
4. Inflammatory oedema to surrounding area
Describe the cerebral abscess
- Definition: An area of suppurative inflammation in the brain substance
- Causes: Staph Aureus, bacteroides, nocardia.
- Characteristics: Consists of a pus-filled cavity surrounded by a fibrogliotic wall (full of astrocytes and fibroblasts) that is usually surrounded by inflammatory oedema.
Discuss the clinical manifestations of the cerebral abscess.
A combination of:
- Space occupying lesions (SOLs) causing usual Ssx of raised ICP (HA, vomiting, papilloedema, focal neuro Ssx)
- Infection Ssx - Fever, malaise, weight loss etc
- Ssx of primary infection (otitis media, suppurative lung disease etc)
If left untreated enlargement may occur, exacerbating Ssx (especially those associated with raised ICP)
How is cerebral abscess diagnosed?
- Cerebral abscess is diagnosed via clinical manifestations and CT/MRI
- Lx puncture is not generally used due to risk of herniation (raised ICP is a clinical features of cerebral abscess).