Week 221 - Meningitis Flashcards
Of the 3 main causes of meningitis (bacterial, viral, fungal) which is the most common form?
Viral
Which has a worse prognosis bacterial or viral meningitis?
Bacterial
What is the initial treatment for suspected meningitis if it presents in the GP?
Antibiotics in case it is bacterial Call 999 (ambulance transfer to hospital) Call hospital to warn of a suspected meningitis case possibly give paracetamol, O2 if necessary / possible
What sort of antibiotics is the GP likely to give and why?
Whilst you would ideally treat with broad-spectrum antibiotics most GPs will have access to penicillin and so that narrow spectrum AB will be used
What it the management process once the patient is admitted to A&E?
ABCDE; Cannulate - Fluids (20mls/kg); bloods
Seizure control
LP when safe / not contraindicated
Get consultant involved and inform public health
What are the signs of shock that may present if sepsis/septicaemia sets in?
Drop in BP (although children hang on to BP longer than adults); reduced urine output (normal = ~1ml/kg/hr); slow cap refill, increase HR
What bloods are you going to want with suspected meningitis?
FBC (WCC up? and Hb down?), ESR, CRP, Cultures, U&E (low Na - inappropriate ADH?), LFT, glucose, coagulation, ABG (acidotic account for any confusion?)
What conditions might predispose a child / someone to meningitis?
Ear or sinus infections
Hydrocephalous (foreign bodies in head used for Tx)
Immunosuppression
List some risk factors for meningitis
Immunosuppression; young; elderly; alcoholism; lack of vaccines; DM; renal / adrenal insufficiency; CF; splenectomy; malignancy; Thalasaemia major
What colour should CSF be normally?
Clear
What structure within the ventricles produces CSF?
the choroid plexus
What colour will CSF be if bacterial meningitis is present?
Cloudy
What other changes, besides cloudiness of the CSF will be found on a CSF film?
High neutrophil count, High protein count, Low or absent glucose
What accounts for the low to absent glucose on a CSF film in the presence of bacterial meningitis?
The bacteria will be using it to replicate and survive
What is the risk associated with increased CSF protein?
Vascular obstruction (protein heavy CSF is thick and goopy) can cause thrombi etc
What will the CSF profile likely be in the presence of viral meningitis?
clear to turbid, lymphocytes high, protein normal to high, glucose normal
If mycobacteria is the cause of meningitis what will the CSF profile look like?
Clear to turbid, v high lymphocytes, v high protein, low glucose
Where is CSF found?
In the subarachnoid space within the meninges - in the ventricles of the brain and the spinal cord
Where does all CSF drain to?
The internal jugular veins (via the sigmoid sinuses)
Which venous sinuses drain the anterior skull base?
The cavernous sinuses
Name the venous sinuses of the brain
The superior and inferior sagittal sinuses
The transverse sinuses
The cavernous sinuses
The sigmoid sinuses
Name the 4 septa of the dura mater
The falx cerebri
The falx cerebelli
The tentorium cerebelli
The diaphragm sellae
What is the relationship between the septa of the dura and the venous sinuses?
The Inferior and Superior Sagittal sinuses follow the inferior and superior surfaces of the Falx Cerebri, and the anterior/posterior surfaces of the Falx Cerebelli
The Transverse sinuses follow the posterior line of the Tentorium Cerebelli
The Cavernous Sinus sits beneath the Diaphragma Sellae
What are the 4 route by which microbes enter the CNS?
via blood (most commonly) via direct implantation (traumatic, iatrogenic, congenital); via local extension of established infections (sinuses, teeth, middle ear) From PNS (rabies, herpes simplex, shingles)
What condition is caused by Herpes Simplex Virus?
Cold sores; genital herpes
What condition is caused by Herpes Zoster Virus?
Chicken Pox; Shingles
At what site do microorganisms cross the blood brain barrier?
The choroid plexus
How is it easier for microorganisms to cross the BBB through the choroid plexus than the brain microvascular endothelial cells (BMEC) of the brain parenchyma?
The BMECs have weaker tight junctions between them, the endothelium is fenestrate increasing permeability, thus intracellular flux is increased
What are the possible early signs and symptoms of meningitis?
severe headache, malaise, fever, lethargy, n&v, irritibility
Sometimes: photophobia, rash, drowsiness progressing to unconsciousness, convulsions, hamstring rigidity
What is Brudzinski’s sign?
A test of meningeal irritation.
With pt supine flex the head towards their chest, involuntary flexion of hips and knees is a +ve Bradzinski’s sign
What is Kernig’s Sign?
A test of meningeal irritation.
With pt supine, flex their hip and knee and then try to extend their knee - back pain and resistance to extension is a +ve Kernig’s sign
What combination of information / findings helps you diagnose meningitis?
signs, symptoms, CSF profiling, culture (perhaps with Kernig’s / Brudzinski’s signs tested for on examination)
What causes the petechial rash sometimes found with meningitis?
Septicaemia. Inflammation causes vessels to become leaky so subepithelial haemorrhage can occur
What terms are used to describe viral meningitis due to the CSF profile it produces?
“Aseptic” or “Lymphocytic”
What viruses usually cause meningitis?
Echoviruses; Coxackie Viruses (A + B); (polio rare now in UK)
Can be as a complication of other viral infections: Mumps; Herpes Simplex; Herpes Zoster; HIV
Anatomically how is encephalitis different to meningitis?
Encephalopathy occurs when the infection affects the brain parenchyma rather than the meninges
Where dose replication typically take place once an enterovirus has been ingested or inhaled?
Oro-pharynx or Peyer’s Patches
In an individual between the ages of 3 months and 65 years what are the most likely organisms to cause BACTERIAL meningitis?
Neisseria meningitidis (meninigococcal) Streptococcus pneumonia (Pneumococcal)
In neonates (<3 months) with bacterial meningitis what is the most likely causative organism?
Group B Streptococcus (Streptococcus agalactiae) (or E. coli according to GP)
What is the most common cause of bacterial meningitis in the UK?
Neisseria meningitidis (gram -ve, capsular)
What is the pathogenesis of Neisseria meningitidis?
nasopharynx > blood > meninges
What is the pathogenesis of Streptococcus pneumonia, Haemophilus influenza and Cryptococcus neoformans?
Resp tract > blood > meninges
List these bacterial pathogens: Hib, Pneumococcus, Meningococcus, in order of severity of meningitis they cause (generally) most to least severe
Pneumoccocus, meningococcus, Hib
How does meningitis develop if Mycobacterium tuberculosis is the causative organism?
Gradual onset, normally with a preceding focal infection elsewhere in the body e.g. lung
What is the pathogenesis of Mycobacterium tuberculosis meningitis?
Resp tract > Blood > meninges > burst from small abscesses then get symptoms
What is the best indicator of a fungal source of meningitis infection?
the India Ink Stain
What organism is responsible for causing most cases of fungal meningitis?
Cryptococcus neoformans (gradual onset of symptoms)
If symptoms are slow to develop what two organisms are likely to have caused the meningitis?
Mycoplasma tuberculosis or Cryptococcus
What is the main cause of encephalitis?
Herpes Simplex Virus (HSV type I)
Physically, what characterises encephalitis?
Extensive, asymmetric, necrosis of temporal lobes (resulting in altered mental status and personality and seizures )
How would you diagnose HSV encephalitis?
Head CT and MRI
What is the treatment for HSV encephalitis?
Aciclovir for 21 days
Reactivation of HSV infection in what area is most associated with HSV encephalitis?
Trigeminal ganglia (mother can also pass to baby through birth canal)
Although ‘pure encephalitis’ (only affecting the parenchyma without meningeal involvement) is rare name a cause of it
Rabies Virus - infects the brain via the PNS
Describe briefly what a brain abscess is, how caused and how treated
Focal infection of brain parenchyma, most caused by bacteria (fungi + parasites can), often result of local extension of infection, blood transportation or direct implantation. CT / MRI, aspiration to diagnose (though difficult so high mortality). Tx: surgical drainage or at least 1month of ABx
Which form of meningitis causes the non-blanching rash and how?
Meningococcal AKA Neisseria meningitidis
