Infections Of The Nervous System Flashcards
What is cerebrospinal fluid (CSF)?
Substance similar to blood plasma with less proteins and few cells produced by choroid plexus in brain ventricles, circulating through the sub-arachnoid space around the brain and spinal cord providing impact protection and metabolic support to the CNS
What is intra-cranial pressure (ICP)?
Pressure inside the skull most easily measured in sub-arachnoid space around the lumbar spine where the spinal cord ends via a lumbar puncture and subsequent measure of opening pressure with an attached manometer (accurate enough if no blockages in CSF circulation e.g. hydrocephalus)
What is the difference between meningitis and encephalitis?
Meningitis is inflammation (usually infectious) of the meninges whereas encephalitis is inflammation (usually infectious) of the brain but clinical features overlap - can also get meningoencephalitis (inflammation of meninges and brain)
What is myelitis?
Inflammation (sometimes infectious) of the spinal cord
What different types of abscess exist in the brain?
Cerebral = in the brain
Epidural = epidural space in area where a epidural puncture has been done
Subdural = subdural space in area where lumbar puncture has been done
What is an abscess?
Collection of pus
What are the causes of bacterial meningitis?
Neisseria meningitidis (meningococcus) Streptococcus pneumoniae (pneumococcus) Group B Streptococci Haemophilus influenzae type B (HiB) Listeria monocytogenes Mycobacterium tuberculosis
What are the viral and fungal causes of meningitis?
Viral: enterovirus, VZV, HIV, mumps and measles (younger people)
Fungal: Cryptococcus neoformans
What are the causes of encephalitis?
Viral: HSV (cold sores), VZV, HIV, arboviruses and rabies
What are the causes of cerebritis?
Bacterial: associated with immunodeficiency or abscesses
What are the causes of abscess?
Bacterial: mostly Streptococci (Pneumoniae most commonly or upper airway/sinus infections)
What are the causes of cysts?
Parasitic: toxoplasmosis, cysticercosis and echinococcosis (hydatid)
What are the causes of myelitis?
Viral: poliomyelitis and rabies
What types of meningitis are currently most common?
Vaccinations against all types of N. Meningitidis and H. Influenzae B so all of these are practically non-existent now so other strains becoming more predominant e.g. viral
Who are the most common individuals to get meningitis?
Infants < 1yr
Younger children
Later teenagers-early 20s (new university students)
Individuals living in the meningitis belt in Africa
Individuals on The Hajj pilgrimage (must get vaccine prior to this now)
Why are university students more prone to meningitis?
Most people naturally carry the germ in the back of their throat causing no problems for them or anyone else but when people start to mix, if they have not been exposed to it before they may become infected
What overlapping clinical syndromes can meningococcal infections cause?
Meningitis on its own (restricted to meninges), septicaemia on its own (all over body but not in meninges) and commonly meningitis and septicaemia together
What are the features of CNS infection?
Focal CNS signs
Fever
Reduced GCS
More common in meningitis: Headache Neckstiffness Photophobia Purpuric rash (ONLY meningococcal meningitis/septicaemia)
More common in encephalitis:
Confusion
Seizures
What is the best motor response scale of the GCS?
6 - obeys commands 5 - localising response to pain 4 - withdraws from pain 3 - flexor (decorticate) response 2 - extensor (decerebrate) response) 1 - no response
What is the best verbal response scale of the GCS?
5 - normal speech 4 - confused speech 3 - inappropriate speech (words only) 2 - incomprehensible (sounds only) 1 - no response
What is the best eye response scale of the GCS?
4 - eyes open spontaneously
3 - eyes open to voice
2 - eyes open to pain
1 - no response
What symptoms are usually sufficient to make a diagnosis of bacterial meningitis?
Any 2 of: Headache Neck stiffness Fever > 38 GCS < 14
Who is most likely to get meningococcal meningitis?
Children and young adults with possible acute outbreaks, sepsis, purpuric rash (beginning of skin gangrene) and peripheral gangrene
Who is most likely to get pneumococcal meningitis?
Associated with RTI, trauma, immunocompromised and elderly individuals with less acute outbreaks (building up over days), no rash, high mortality and morbidity
Who is most likely to get Group B Streptococcus meningitis?
Neonates acquire the bacteria during birth as the mother may carry it - low morality but still risk of CNS damage
Who is most likely to get Listeriosis meningitis?
Neonates, elderly, immunocompromised and pregnant individuals - meningoencephalitis, rhomboencephalitis with blood cultures +ve
How does Tuberculosis meningitis typically present?
Insidious onset of fever, confusion, coma, high CSF protein (~8ml required for culture)
Who is most likely to get brain abscess meningitis?
Associated with chronic URTIs e.g. sinusitis and otitis, immunocompromised or individuals with learning disabilities (not good at expressing whats wrong with them) with insidious onset or seizure presentation
What investigations should you consider in a patient with head injury?
FBCs & inflammatory markers (e.g. CRP)
Renal function (U+Es)
Coagulation tests (APTT/PT)
Consider CT head if risk of raised ICP or brain lesions
LP
CSP opening pressure/appearance
Additional tests for M. Tuberculosis and Cryptococcus
What do you want to test for in a lumbar puncture when the patient has head injury?
Sample 1 + 3 sent for microscopy/microbiology - RCC/WCC and differential, organisms and PCR tests (if you’ve punctured a vessel, 1 will have a lot of RBCs but 3 will have less whereas consistent blood indicates a problem)
Sample 2 sent for biochemistry - protein/glucose with blood glucose to compare
Why do you want to test renal function in head injury patients?
Kidney function can be damaged during sepsis
Why do you need to do a coagulation test in head injury patients?
Make sure patient has normal clotting before performing a lumbar puncture
What is there a risk of when doing a lumbar puncture in patients with raised intracranial pressure (ICP)?
Coning - brain herniating through the foramen magnum crushing the base of the brain = life-threatening consequences - why you do a CT head before doing a lumbar puncture if there are indications of raised ICP (otherwise don’t bother)
Why do you do 2 sets of blood cultures in head injury patients?
To avoid contamination when time is of such essence
What will you see in a CT if there is raised intracranial pressure (ICP)?
Midline shift
Loss of sulci and ventricles
Where do you do a lumbar puncture?
Above spinous process of L4 roughly
What layers will you go through when performing a lumbar puncture?
Skin Subcutaneous tissue Supraspinous ligament Interspinal ligament Ligamentum flavum Epidural space (contains internal vertebral venous plexus) Dura Arachnoid Subarachnoid space
What should cerebrospinal fluid (CSF) look like?
Clear and colourless with a tinge of yellow
What might a patient with meningitis cerebrospinal fluid (CSF) look like?
Turbid cloudy appearance due to bacteria however this is not seen so much now as patients present earlier
What cerebrospinal fluid (CSF) results are abnormal?
Opening pressure > 18cm of water using manometer
RCC > 1 per mm^3 (either traumatic LP or SAH so compare bottles 1 and 3)
WCC > 5 per mm^3
Protein > 1g/L and glucose < 50% of blood glucose
What will the cerebrospinal fluid (CSF) show in a bacterial infection?
High WCC > 5 per mm^3 mostly neutrophils
High protein > 1g/L
Low glucose < 50% of blood glucose
What will the cerebrospinal fluid (CSF) show in a viral infection?
Slightly high WCC > 5 per mm^3 mostly lymphocytes
Slightly high proteins > 1g/L
Normal glucose in comparison to blood glucose
What will the cerebrospinal fluid (CSF) show in tuberculosis infection?
High WCC > 5 per mm^3 mostly lymphocytes
Very high protein > 1g/L
Low glucose < 50% of blood glucose
What type of White Blood Cell (WBC) will be high if there is an abscess?
Lymphocytes
How do you manage a CNS infection?
- Supportive treatment and Sepsis
2. Find right antibiotic for cause
How do you treat bacterial meningitis?
Ceftriaxone, Cefotaxime or Benzylpenicillin (penetrate BBB well)for 1 week with Dexamethasone IV QDS for 4 days
If severe Penicillin allergy give Vancomycin, Meropenem, Rifampicin or Cotrimoxazole
How do you treat listeriosis?
Amoxicillin IV QDS for 3 weeks
How do you treat viral encephalitis?
Aciclovir IVTDS for 3 weeks
How do you treat tuberculosis?
Rifampicin, Isoniazid, Pyrazinamide, Ethambutol and Dexamethasone IV QDS for 1 week converted to
Why is Dexamethasone given in CNS infections?
If infection is severe, there may be cranial nerve compression injuries which may induce permanent damage if not dealt with by this steroid - benefit small but in certain cases its recommended
What is the prognosis of meningococcal meningitis (w/o septicaemia)?
Mortality ~10%
CN palsies e.g. deafness and squints
Post-infective immunological complications e.g. arthritis and pericarditis
What is the prognosis of meningococcal septicaemia (sepsis with or w/o meningitis)?
Mortality ~40% (higher as patients present later due atypical signs unlike meningitis)
Gangrene of purpura and peripheries - produces ulcers that could cause patient to lose limbs or heal if caught early
Post-infective immunological complications e.g. arthritis and pericarditis
What is the prognosis of pneumococcal meningitis?
Mortality ~25%
CN palsies e.g. deafness
Relapses (even after a week of treatment) and metastatic infections
What chemoprophylaxis can be used for meningococcus infection?
For household and kissing contacts - Ciprofloxacin single dose and Rifampicin BD for 2 days
Not required for patient is treated with Ceftriaxone
What immunoprophylaxis can be used for meningitis?
Vaccines against:
- Meningococcus A, C, W135, Y and now B
- Pneumococcus (7 serotypes)
- Haemophilus Influenzae type B (HiB)
- Some viral causes of meningitis
