Central Nervous System Infections Flashcards
Meningitis routes of infection
Blood Bourne
Parameningeal suppurations-> otitis media, sinusitis-> infections which are good at getting through meninges
Direct spread though Duran defect-> surgery, trauma
Direct spread though cribriform plate
Meningitis definition
Inflammation of the meninges
- > leptomeningitis-> inflammation centred on the subarachnoid space
- > pachymeningitis->inflammation centred on dura
CSF infection
Difficult to treat Low protein-> no complement etc Low IgG No lymphatics BBB-> drugs need to by lymphilic
Bacterial Meningitis inflammatory process
Endotoxins of gram negative bacteria and peptidoglycan components of gram positive cell walls-> potent inflammatory mediators-> TNF, IL-1,6,8, PAF, NO. Can resist phagocytosis-> bacteriaemia
- > migration of neutrophils to the CSF-> release of proteolytic products and O radicals
- > damage to vascular endothelium-> increased BBB permeability
- > alteration of CSF dynamics
Meningitis symptoms and signs
Global headache
Neck and back stiffness
Nausea and vomiting
Photophobia
Fever, can be absent in really bad infection
Petechial/purpuric rash
Kernigs signs positive due to hamstring spasm, neck stiffness-> can’t put head on chest
Clinical features of meningitis
Fever 97% Meningism 82% Impaired conciousness Rash Seizures Hypotension
Meningitis in infants
Typical signs are not always present <18/12 Flaccid later opisthotonos Bulging fontanelle due to increased ICP Fever and vomiting often the only sign Strange cry Convulsions
Lumbar puncture
Most rapid diagnostic test Distinguish between bacterial and viral Risk of herniation (coning)from increase intra cranial pressure -> if longer history -> focal neurology, drowsy Only do it if not contraindicated Treat first
CT scan
Benefits-> identifies SOL or other lesion, very rarely show meningeal flare Disadvantages: Delay Doesn't help diagnosis of meningitis Poor predictor of raised ICP Poor distinction between com/non com hydrocephalus Indicated when: -> diagnosis is in doubt -> focal abnormalities -> com or seizures non urgent
CSF changes in meningitis
Normally < 5 lymphocytes
Blood glucose should be half that in blood
Viral-> 50-1000 WBC, predominately mononuclear neutrophilic
Bacterial-> 100-5000 WBC, predominately neutorphilic, low glucose
TB-> 50-300 WBC, mononuclear
Cryptococcal-> 20-500, mononuclear
Causes of lymphocytic CSF
TB Partially treated bacterial infection Leptospirosis Lyme borreliosis Viral meningo-encephalitis Syphillis Lymphocytic Leukaemias
Rapid diagnostic tests for meningitis
Gram stain on deposit 50% sensitivity Agglutination tests look for antigen-> meningococcal! HiB, cryptococcal PCR -> meningococcal on EDTA blood and CSF HSV/Enterovirus Mtb
Causes of bacterial meningitis
Neisseria meningitis-> children/ young adults
Streptococcus pneumoniae-> children vaccine
Group B streptococci, eschrichia coli, listeria monocytogenes-> neonates
Pneumococcal meningitis
Predisposing factors-> alcohol, diabetes, hypospenism, myeloma, immunosuppression
Pneumonia and/or otitis media present in <50%
Impaired consciousness, neurological signs and seizures more common
Morality 30% with therapy
Listeriosis
Poo and contaminated fridge food Meningo-encephalitis Affects brain stem with ataxia and movement disorders, neck stiffness Gram stain negative Ampicillin +\- gentamicin Morality 20%
Complications of meningitis
Death Subdural collection Cerebral vein thrombosis Hydrocephalus 9-15% deafness convulsions Visual/motor/ sensory deficit
Management of meningitis
Antibiotics
Adequate oxygenation
Prevention of hypoglycaemia and Hyponatraemia
Anticonvulsants
Decrease intracranial hypertension
Steroids-> give prior to antibiotics for beneficial effect
Causes of viral meningitis
Enteroviruses
Herpes viruses-> heroes simplex, varicella zoster
Mumps and measles
Flavaviruses
Encephalitis
Inflammation of the brain Cerebral irritation/dysfunction: -> irritability, altered personality, drowsiness -> ataxia -> excessively brisk tendon reflex -> signs of cerebral/brain stem failure -> signs of brain swelling Myelopathy->motor and sensory signs Encephalopathy-> reduced conciousness
Organisms that cause encephalitis
Viral-> herpes simplex, polio, rabies
Bacterial-> listeria! treponema, borrelia
Myelitis
Inflammation of the spinal chord
Can occur with or without encephalitis
Transverse-> acute transaction of spinal chord
-> vasculitis of anterior spinal artery
-> primary infection-> VZV , TB, syphlis, schistosomiasis
-> post infectious-> measles, mumps, rubella, upper resp
-> direct invasion of spinal chord-> VZV, borrelia, HTLV-1 throaric
Ascending-> ascending flaccid paralysis and sensory loss
Anterior horn cells eg polio flaccid paralysis muscle pain, no sensory or bladder dysfunction-> polio, Enterovirus 71, some arboviruses and rabies virus
Encephalomyelitis
Encephalitis and myelitis as over lapping causes
Primary or post infection
Direct invasion, vasculitis interrupting blood supply or immune response to infection
Entry to CNS for Encephalomyelitis
Blood most common
Some via peripheral nerves-> rabies and polio
Respiratory-> measles, mumps, VZV, c.neoformans
GI tract-> poliovirus, other enteroviruses, listeria
Subcutaneous-> arthropod Bourne viruses, ricketsii, trypanosomes
Mucosa-> herpes simplex, VZV
Herpes simplex encephalitis
Haemorrhagic necrosis especially in temporal lobes CSF abnormal in 97% RBCs in an atraumatic LP Mild lymphocytosis Characteristic MRI Morality 60% if left untreated
