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Year 3 Neuroscience > Infections > Flashcards

Infections Flashcards

1
Q

What is encephalitis?

A

Inflammation of the brain parenchyma.

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2
Q

What is parenchyma?

A

The functional tissue of an organ as distinguished from the connective and supporting tissue

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3
Q

What is the aetiology of encephalitis? (x4)

A
  • 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
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4
Q

What is the pathophysiology of encephalitis?

A

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).

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5
Q

What is the epidemiology of encephalitis: Incidence? Age?

A

Incidence in UK is 7.4 in 100 000. Under 1 or over 65.

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6
Q

What are the risk factors of encephalitis? (x6)

A

History of seizures, immunodeficiency, transplant, insect/animal bites, location, season.

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7
Q

What are the symptoms of encephalitis?

A
  • 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
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8
Q

What are the signs of encephalitis? (x7)

A
  • 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
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9
Q

What is meningism?

A

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.

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10
Q

What are the blood investigations for encephalitis? (x6)

A
  • 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
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11
Q

What are the other investigations for encephalitis? (x4)

A
  • 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
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12
Q

What are the diagnostic criteria for encephalitis?

A
  • 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.
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13
Q

What is meningitis?

A

Inflammation of the leptomeningeal (pia and arachnoid) coverings of the brain, most commonly from infection.

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14
Q

What is the aetiology of meningitis? (x5)

A
  • BACTERIAL
  • VIRAL: enteroviruses, mumps, HSV, VZV, HIV
  • FUNGAL: Cryptococcus (associated with HIV infection)
  • Aseptic meningitis
  • Mollaret’s meningitis
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15
Q

What are the bacterial causes of meningitis: Neonates? Children? Adults? Elderly?

A
  • 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
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16
Q

What is aseptic meningitis? Aetiology? (x6)

A

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).

17
Q

What is Mollaret’s meningitis? Aetiology? CSF? (x2)

A

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.

18
Q

What is the pathophysiology of bacterial meningitis?

A
  • 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
19
Q

What is meningococcal meningitis?

A

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.

20
Q

What is the pathophysiology of viral meningitis?

A
  • 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.
21
Q

What is the pathophysiology of fungal meningitis?

A

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)

22
Q

What is the epidemiology of meningitis: Bacterial distribution? Fungal distribution? Age?

A
  • 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
23
Q

What are the risk factors for bacterial meningitis? (x8)

A

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.

24
Q

What are the risk factors for viral meningitis? (x4)

A

Young age, summer and autumn (for enteroviruses), immunosuppression, exposure to rodents.

25
Q

What are the risk factors for fungal meningitis? (x6)

A

HIV infection (due to loss of CD4+ T helper cells), corticosteroids, underlying chronic disease, immunodeficiency, environmental exposure, cranial anatomy (basal skull fractures, CSF shunts, intracranial surgery)

26
Q

What are the symptoms of meningitis? (x8)

A
  • Meningism: headache, neck stiffness, backache and photophobia
  • Nausea and vomiting
  • Irritability
  • Drowsiness
  • Clouding of consciousness
  • Fever
  • Seizures
  • Symptoms of hydrocephalus in fungal meningitis: impaired cognitive function, lack of coordination, and urinary incontinence.
27
Q

What are the signs of meningitis? (x4)

A
  • Signs of meningism from stretching meninges: including Kernig’s sign – with hips flexed, pain/resistance on passive knee extension; Brudzinski’s sign – flexion of hips on neck flexion
  • Signs of infection: fever, tachycardia, hypotension
  • Skin rash (more common in viral meningitis; petechiae with meningococcal septicaemia)
  • Altered mental state
28
Q

What are the blood investigations for meningitis? (x3 +4)

A
  • Two sets of blood cultures for bacterial, three sets for fungal blood cultures
  • PCR bacterial DNA, viral DNA and fungal DNA
  • FBC: high WCC, low RBC and platelets
  • VBG: lactate may be elevated
  • SCREEN COMPLICATIONS:
  • Glucose: as hypo/hyperglycaemia is a complication of bacterial meningitis
  • U&Es: metabolic abnormalities is a complication of severe bacterial meningitis
  • LFTs: raised as a complication of severe bacterial meningitis
  • Coagulation screen: abnormalities common in severe infection
29
Q

What are the other investigations for meningitis? (x4)

A
  • CT: exclude mass lesion or increased intracranial pressure before lumbar puncture (may lead to cerebral herniation during CSF removal).
  • LUMBAR PUNCTURE: note opening CSF pressure. Send CSF for microscopy, culture, sensitivity, Gram staining, biochemistry and cytology
  • PETECHIAE SCRAPINGS: staining may detect meningococcus in 70% of patients
  • VIRAL PCR and HIV TEST
30
Q

!!! General: What are the indications for CT head BEFORE lumbar puncture? (x6)

A

A CT must be done before LP in patients with immunodeficiency, history of CNS disease, decreased consciousness, fit, focal neurological deficit or papilledema. This is because risk of mass lesion or increased intracranial pressure is higher, and these must be excluded due to risk of cerebral herniation during CSF removal.

31
Q

! What would lumbar puncture show in bacterial, viral and fungal meningitis?

A
  • BACTERIAL: cloudy or purulent, raised opening pressure, high neutrophils, low glucose (less than 50%), high protein, high lactate. Can also do microscopy, Gram stain, culture and sensitivities.
  • VIRAL: clear, normal/high opening pressure, LYMPHOCYTOSIS, glucose over 60% (i.e., normal; low in HSV infection), high protein, low lactate. Can also do CSF viral PCR
  • FUNGAL: clear/cloudy, raised opening pressure (usually highest), low glucose, high protein. In other words, same as bacterial. Can also do fungal cultures and antibody/antigen tests.
32
Q

How is bacterial meningitis managed? (x5 antibiotic examples)

A
  • Immediate IM/IV antibiotics before any investigation if meningitis suspected: cephalosporin, benzylpenicillin for meningococci and pneumococci, amoxicillin and gentamicin for Listeria, add vancomycin if resistance, give rifampicin for 2 days after.
  • Dexamethasone IV: for 4 days. Reduce risk of complications
33
Q

How is viral meningitis managed?

A
  • Treat with antibiotics until viral or fungal is identified:
  • Supportive care, and antivirals in HSV, varicella zoster or CMV aetiology (acyclovir or valaciclovir IV and orally respectively, every 8 hours)
34
Q

How is fungal meningitis managed?

A
  • Antifungal induction therapy: amphotericin IV and flucytosine/fluconazole orally for two weeks
  • Add antiretroviral therapy for HIV patients
  • Maintenance therapy with fluconazole
  • CSF drainage for hydrocephalus if opening CSF pressure is too high
35
Q

How is meningitis prevented? (x3)

A
  • Notifiable disease
  • Chemoprophylaxis (usually rifampicin course) and vaccination for close contacts
  • Vaccination against meningococcal serogroups A and C.
36
Q

What are the complications of meningitis? (x9)

A
  • Cranial nerve palsies from compression associated with cerebral oedema
  • Septicaemia and septic shock in bacterial
  • DIC
  • Renal failure
  • Fits
  • Peripheral gangrene
  • Cerebral venous thrombosis
  • Hydrocephalus
  • Water-house-Friderichsen syndrome (bilateral adrenal haemorrhage)
37
Q

What is the prognosis of meningitis?

A

Bacterial has high mortality rate (10-40% with meningococcal sepsis). Viral meningitis often self-limiting. Fungal has high mortality.

Year 3 Neuroscience (14 decks)

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