Infections of the Nervous System Flashcards
What is meningitis?
Inflammation/infection of the meninges
What is encephalitis?
Inflammation/infection of brain substance
What is myelitis?
Inflammation/infection of spinal cord
In reality what is the distinction between meningitis, encephalitis and myelitis?
The distinction is artificial and patients often have a mixture
What is the classical triad of meningitis?
- Fever
- Neck stiffness
- Altered mental status
How do patients with meningitis present?
With short history of progressive headache associated with fever (>38 degrees) and meningism (neck stiffness, photophobia, nausea + vomiting)
How is neck stiffness examined?
By passively bending the neck forward
What is commonly found in meningitis?
Cerebral dysfunction = confusion, delirium, declining conscious level, GCS <14 in 69%
What 2 symptoms can occur in about 30% of meningitis patients?
- Cranial nerve palsy
- Seizures
(not necessarily both)
What symptoms occurs in 10-20% of meningitis patients?
Focal neurological deficits
What is the hallmark of meningococcal meningitis (but can also occur in viral meningitis)?
Petechial rash (tumbler test)
What are the infective causes of meningitis?
Bacterial (neisseria meningitidis (meningococcus), strep pneumoniae (pneumococcus))
Viral (enteroviruses)
Fungal
What is an inflammatory cause of meningitis?
Sarcoidosis
What are the drug related causes of meningitis?
NSAIDs
IVIG (IV immunoglobin)
What are the malignant causes of meningitis?
Metastatic
Haematological
e.g. Leukaemia, lymphoma, myeloma
What are the main features of encephalitis?
- Flu-like prodrome (4-10 days)
- Progressive headache associated with fever
What are other features found in encephalitis?
+/- meningism
Progressive cerebral dysfunction (confusion, abnormal behaviour, memory disturbance, depressed conscious level)
Seizures
Focal symptoms/signs
What is the different between viral and bacterial encephalitis?
Onset of viral encephalitis is slower than bacterial and cerebral dysfunction is a more prominent feature
What is a viral cause of encephalitis?
Most commonly HSV
What are inflammatory causes of encephalitis?
Limbic encephalitis (Anti VGKC, Anti NMDA receptors) ADEM
What are metabolic causes of encephalitis?
Hepatic
Uraemic
Hyperglycaemic
What are malignant causes of encephalitis?
Metastatic
Paraneoplastic
What other form of encephalitis is as common as viral encephalitis?
Auto-immune encephalitis
What are the 2 important antibodies for auto-immune encephalitis?
Anti-VGKC (voltage gated potassium channel)
Anti-NMDA receptor
Describe anti-VGKC auto-immune encephalitis
- frequent seizures
- amnesia (not able to retain new memories)
- altered mental state
Describe anti-NMDA receptor auto-immune encephalitis
- flu-like prodrome
- prominent psychiatric features
- altered mental state and seizures
- progressing to a movement disorder and coma
What is the priority when investigating meningitis and encephalitis?
To exclude (and treat) infection
What are the 2 methods of investigation for meningitis?
- Blood cultures (bacteraemia)
- Lumbar puncture (CSF culture/microscopy)
No need for imaging if no contraindications to LP
What are the 4 methods of investigation for encephalitis?
- Blood cultures
- Imaging (CT scan +/- MRI)
- Lumbar puncture
- EEG
What are the 5 indications for CT scan before lumbar puncture?
Focal neurological deficit, not inc cranial nerve palsies
New-onset seizures
Papilloedema
Abnormal level of consciousness, interfering with proper neurological examination (GCS <10(
Severe immunocompromised state
What do focal symptoms and signs suggest?
A focal brain mass
What does reduced conscious level suggest?
Raised ICP
Is lumbar puncture safe to carry out in meningitis?
Yes as brain is ‘okay’; if problem is with brain - scan first
Describe the CSF finding of opening pressure in bacterial meningitis vs viral meningitis and encephalitis
BM = increased
VM/E = normal/increased
(gives idea of what kind of infection you are dealing with)
Describe the CSF finding of cell count in BM vs VM/E
BM = high, mainly neutrophils (polymorphs)
VM/E = high, mainly lymphocytes (mononuclear cells)
(main thing to look at in diagnosis)
Describe the CSF finding of glucose in BM vs VM/E
BM = reduced (bacteria use up glucose) VM/E = slightly increased
Describe the CSF finding of protein in BM vs VM/E
BM = high VM/E = slightly increased
First line treatment in suspected meningitis?
IV CEFTRIAXONE
What does a cloudy CSF indicate?
Large number of cells in sample
What should you do if the patient is presenting septic or pyrexial?
Do lumbar puncture but not blood culture
What is the commonest cause of encephalitis in Europe?
HSV (herpes simplex virus)
How is herpes simplex encephalitis diagnosed in the lab?
By PCR of CSF for viral DNA
What treatment should be given on clinical suspicion of herpes simplex encephalitis?
ACICLOVIR (then take sample and adapt with results)
What does a blood culture gram stain look like in bacterial meningitis?
Gram positive cocci in chains (look like streptococci)
Culture strep pneumoniae sensitive to penicillin
What is an appropriate investigation for herpes simplex encephalitis?
Lumbar puncture
What are the other 3 of the herpes group of viruses other than HSV?
VZV, EBV, CMV
What does HSV generally cause (types 1 + 2)?
- Cold sores (type 1 > 2)
- Genital herpes (type 1 + 2)
Where does the virus remain latent in HSV after primary infection?
In trigeminal or sacral ganglion (as with all herpes viruses - once infected, always infected - dormant until reduction of immunity etc)
What is a rare complication of HSV?
Encephalitis
Other than neonates, what type of HSV is encephalitis caused by?
Type 1
What are enteroviruses a large family of?
RNA viruses
What do enteroviruses have a tendency to cause?
CNS infections (neurotropic) (human infections, no animal reservoir)
How are enteroviruses spread?
Faecal-oral route
What type of meningitis can enteroviruses cause?
Non-paralytic
What 3 viruses are included in enteroviruses?
Polioviruses, coxsackieviruses, echoviruses
What other cause of encephalitis is common in other parts of the world?
Arbovirus encephalitides
How are arbovirus encephalitides transmitted?
To man via a vector (mosquito or tick) from non-human host
What types of encephalitis are caused by arbovirus encephalitides (variety of virus groups)?
- West Nile groups
- St Louis encephalitis
- Western Equine encephalitis
- Tick Borne encephalitis
- Japanese B encephalitis
Why is arbovirus called arbovirus?
ARthropod BOrne
What part of clinical history is crucial in diagnosing arbovirus encephalitide caused encephalitis?
Travel (travel history; some preventable by immunisation)
What is brain abscess?
Localised area of pus within the brain
What is a subdural empyema?
Thin layer of pus between the dura and arachnoid membranes over the surface of the brain
What are some features found in a patient with brain abscess and empyema?
- Fever/pressure headache
- Focal headache/signs
- Signs of raised ICP
- Meningism may be present (esp w empyema)
- Features of underlying source
What are focal symptoms/signs of brain abscess/empyema?
Seizures, dysphasia, hemiparesis
What are signs of raised ICP?
Papilloedema, false localising signs, depressed conscious level
What are some features of underlying source found in brain abscess/empyema?
Dental, sinus or ear infection
What are some differential diagnoses for brain abscess and empyema?
- Any focal lesion, but most commonly tumour
- Subdural haematoma
List 4 causes of brain abscess and empyema
Penetrating head injury
Spread from adjacent infection (dental, sinusitis, otitis media)
Blood borne infection (bacterial endocarditis)
Neurosurgical procedure
List 4 methods of diagnosing brain abscess/empyema
- Imaging (CT or MRI)
- Investigate source
- Blood cultures
- Biopsy (drainage of pus)
What types of organisms are present in brain abscess?
Often mixtures of organisms present (polymicrobial) - dependant on predisposing condition
Strep in 70% cases (esp penicillin-sensitive strep milleri)
Anaerobes in 40-100% cases (bacteroides, prevotella)
What are 6 methods of management for brain abscess? (high mortality without appropriate treatment)
- Surgical drainage if possible
- Penicillin or ceftriaxone to cover strep
- Metronidazole for anaerobes
- High doses required for penetration
- Culture and sensitivity tests on aspirate provide useful guide
