Infections Flashcards
(37 cards)
What is encephalitis?
Inflammation of the brain parenchyma.
What is parenchyma?
The functional tissue of an organ as distinguished from the connective and supporting tissue
What is the aetiology of encephalitis? (x4)
- VIRUS: most common. In the UK, commonly this is HSV. Other viruses are herpes zoster, mumps, adenovirus, coxsackie, echovirus, enteroviruses, measles, EBV, HIV, rabies, Nipah (Malaysia) and arboviruses.
- NON-VIRAL: such as syphilis and Staph. aureus
- IMMUNOCOMPROMISED: CMV, toxoplasmosis, Listeria
- AUTOIMMUNE or PARANEOPLASTIC (abnormal immune response to cancerous tumour): may be associated with antibodies such as anti-NMDA or anti-VGKC
What is the pathophysiology of encephalitis?
In viral encephalitis, the virus initially gains entry in local tissue such as GI tract, skin, respiratory system. There is then subsequent dissemination to the CNS by haematogenous routes (in enteroviruses, HIV, arboviruses) or via retrograde axonal transport (in HSV, rabies).
What is the epidemiology of encephalitis: Incidence? Age?
Incidence in UK is 7.4 in 100 000. Under 1 or over 65.
What are the risk factors of encephalitis? (x6)
History of seizures, immunodeficiency, transplant, insect/animal bites, location, season.
What are the symptoms of encephalitis?
- Often mild and self-limiting
- Symptoms associated with aetiology e.g., rash from HSV
- Subacute onset (hours to days) of headache, fever, vomiting, neck stiffness, photophobia (in other words, symptoms of meningism) with behavioural changes, drowsiness and confusion
- Focal neurological symptoms may be present such as dysphasia and hemiplegia
What are the signs of encephalitis? (x7)
- Decreased level of consciousness
- Seizures
- Pyrexia
- Signs of meningism: including Kernig’s test positive.
- Signs of raised CIP: hypertension, bradycardia, papilledema
- Focal neurological signs
- Mini mental examination may reveal cognitive impairment
What is meningism?
Clinical syndrome of headache, neck stiffness and photophobia, often with nausea and vomiting. It is most often caused by inflammation of the meninges (see below), but other causes include raised intracranial pressure.
What are the blood investigations for encephalitis? (x6)
- Raised WCC, though be aware lymphocytosis may be present in some viral causes
- Blood smear in cases of suspected malarial cause
- U&Es: depending on cause, may see hyponatraemia in Rickettsia (tick-borne bacterial infection) or SIADH
- LFTs: raised in EBV, Rickettsia, tick-borne diseases
- Blood culture: for systemic bacterial infections and most arboviruses
- Serology: IgM, IgG antibodies for viral aetiologies
What are the other investigations for encephalitis? (x4)
- MRI/CT: recommended investigation in suspected encephalitis – preferably MRI. Excludes mass lesion. Can identify various aetiologies e.g., HSV produces characteristic oedema of the temporal lobe on MRI.
- Sputum culture, nasopharyngeal aspirate and throat swab: detect aetiology
- LUMBAR PUNCTURE: CSF analysis shows raised lymphocytes, monocytes, protein, normal/low glucose. Can also determine aetiology with viral PCR.
- EEG: may show epileptiform activity e.g., spiking activity in temporal lobes
What are the diagnostic criteria for encephalitis?
- Patients must present with altered mental status (e.g., altered consciousness, lethargy, personality change) lasting at least 24 hours
- At least two of the following: pyrexia, seizures, new onset focal neurological findings, CSF raised WCC, abnormal imaging, abnormal EEG
- Confirmation requires one of the following: pathological confirmation of brain inflammation, evidence of acute infection with microorganism strongly associated with encephalitis, or evidence of autoimmune condition strongly associated with encephalitis.
What is meningitis?
Inflammation of the leptomeningeal (pia and arachnoid) coverings of the brain, most commonly from infection.
What is the aetiology of meningitis? (x5)
- BACTERIAL
- VIRAL: enteroviruses, mumps, HSV, VZV, HIV
- FUNGAL: Cryptococcus (associated with HIV infection)
- Aseptic meningitis
- Mollaret’s meningitis
What are the bacterial causes of meningitis: Neonates? Children? Adults? Elderly?
- NEONATES: Group B streptococci, E. coli, Listeria monocytogenes
- CHILDREN: Haemophilus influenzae, Neisseria meningitidis, Strep. pneumoniae
- ADULTS: Neisseria meningitidis, Strep. pneumoniae, TB
- ELDERLY: Strep. pneumoniae, Listeria monocytogenes
What is aseptic meningitis? Aetiology? (x6)
Characterised by clinical and laboratory evidence of meningeal inflammation and negative routine bacterial cultures. May be secondary to enterovirus (most common cause), mycobacteria, fungi, autoimmune (sarcoidosis, SLE), malignancy (lymphoma, leukaemia) or medication (NSAIDs, trimethoprim).
What is Mollaret’s meningitis? Aetiology? CSF? (x2)
Recurrent benign lymphocytic meningitis. 50% exhibit transient neurological manifestations. The most common cause is HSV-2. CSF contains large granular plasma cells and presence of HSV.
What is the pathophysiology of bacterial meningitis?
- Bacteria reach the CNS by haematogenous spread (most common route), or direct extension from contiguous site. Bacteria multiplies quickly once they have entered the subarachnoid space (between arachnoid and pia).
- Bacterial components in the CSF induce the production of inflammatory mediators which result in leukocyte migration into the CSF.
- Inflammatory cascades lead to cerebral oedema and increased intracranial pressure which result in neurological damage and death
What is meningococcal meningitis?
Meningococcal meningitis is a form of meningitis caused by a specific bacterium known as Neisseria meningitidis which may progress rapidly to septic shock with hypotension, acidosis, and disseminated intravascular coagulation.
What is the pathophysiology of viral meningitis?
- Viruses replicate outside of the CNS then reach the CNS by haematogenous spread. Viral penetration of the BBB occurs by infection of endothelial cells or of migrating leukocytes.
- Some may also spread by retrograde spread along peripheral nerves such as HSV
- Once in the CNS, virus spreads through subarachnoid space and may infect neurons and glial cells leading to encephalitis and myelitis.
- Immune response to the virus in the CNS leads to lymphocyte accumulation in CSF and inflammatory cytokine release. The inflammatory response increases BBB permeability and allows diffusion of immunoglobulins into CSF.
What is the pathophysiology of fungal meningitis?
With the notable exception of Candida species, many fungal pathogens are thought to be acquired through inhalation. Meningeal involvement, either isolated or associated with widely disseminated infection, results from haematogenous dissemination from the lungs. Immune response leads to raised intracranial pressure and hydrocephalus (CSF accumulation)
What is the epidemiology of meningitis: Bacterial distribution? Fungal distribution? Age?
- Bacterial higher in less developed countries. Lower in highly developed countries due to introduction of Haemophilus influenza type b (Hib), and pneumococcal vaccines.
- Fungal aetiology is confined to specific geographical areas, notably N. Australia, Papua New Guinea, Vancouver Island
- Viral and fungal have their highest incidence in children. Bacterial increases incidence with age
What are the risk factors for bacterial meningitis? (x8)
Advanced age, crowding (close communities such as dormitories), cranial anatomy (basal skull fractures, CSF shunts, intracranial surgery), immunodeficiency, adjacent infections (mastoiditis, sinusitis, inner ear infections), alcoholism and diabetes (both for Listeria monocytogenes), sickle cell anaemia.
What are the risk factors for viral meningitis? (x4)
Young age, summer and autumn (for enteroviruses), immunosuppression, exposure to rodents.
