CNS infection & CSF flashcards
14 high-yield MRCP Part 1 cards from the Intellect Medicos Neurology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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What is the empirical IV antibiotic for suspected bacterial meningitis in an adult with no risk factors for Listeria (NICE 2024)?
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IV ceftriaxone.
Why? Ceftriaxone covers pneumococcus, meningococcus and Hib, the main causes in this age group.
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What is added to empirical ceftriaxone for bacterial meningitis in a patient aged 60 or over, and why?
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IV amoxicillin (or ampicillin), to cover Listeria monocytogenes.
Why? Listeria is a cause in older and immunocompromised adults and is resistant to cephalosporins.
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In suspected bacterial meningitis, when should IV dexamethasone be avoided?
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When meningococcal disease (e.g. meningococcal septicaemia with a spreading non-blanching rash) is the picture: NICE says do not routinely give corticosteroids in meningococcal disease.
Why? Dexamethasone reduces neurological complications mainly in pneumococcal and Hib meningitis. In meningococcal septic shock, only low-dose replacement steroids are considered if pressors fail.
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What chemoprophylaxis is given to close contacts of a case of meningococcal meningitis?
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A single oral dose of ciprofloxacin (any age, including pregnancy). Rifampicin if ciprofloxacin is contraindicated or resistance is likely (e.g. a case linked to travel to the Middle East or Asia).
Why? Prophylaxis clears nasopharyngeal carriage and cuts secondary cases. Close contacts are people with prolonged household-type contact in the 7 days before onset; give it as soon as possible.
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In suspected meningitis, when should CT head be done before lumbar puncture?
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When there are signs of raised ICP or a possible mass lesion: new focal neurological signs (including seizures or posturing), abnormal pupil reactions, GCS 9 or less, or a rapid or sustained fall in consciousness.
Why? CT is not routinely needed before LP. It is done when there is a risk of coning or a focal lesion.
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CSF: fibrin web, white cells 300/µL (mainly lymphocytes), protein 2.5 g/L, CSF:serum glucose ratio 30%, raised opening pressure. What is the likely diagnosis, and which CSF test is preferred to confirm it?
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TB meningitis; nucleic acid amplification test (NAAT) for TB DNA (preferred over Ziehl-Neelsen staining).
Why? Lymphocytes with very high protein and low glucose fit TB. NAAT is more sensitive and faster than smear microscopy.
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What is the treatment of suspected herpes simplex encephalitis?
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IV aciclovir, started immediately on suspicion.
Why? Untreated HSV-1 encephalitis causes haemorrhagic necrosis of the temporal lobes and has high mortality. Starting early improves outcome.
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What is the diagnostic test for herpes simplex encephalitis?
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HSV PCR on CSF.
Why? PCR is the definitive test. Supporting findings are temporal-lobe T2/FLAIR change on MRI and temporal periodic lateralised discharges on EEG.
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What is the most common organism causing a brain abscess?
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Streptococcus milleri group (e.g. S. anginosus).
Why? Most abscesses spread from nearby ear, sinus or dental infection. Haematogenous spread (e.g. endocarditis) is the other route.
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What is the empirical antibiotic regimen for a brain abscess?
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IV third-generation cephalosporin (e.g. ceftriaxone) plus metronidazole.
Why? This covers streptococci and the anaerobes that come from ear, sinus and dental sources.
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Dexamethasone was started for suspected bacterial meningitis. Which confirmed organisms mean it should be continued (NICE 2024)?
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Streptococcus pneumoniae or Haemophilus influenzae type b. Stop it for other organisms.
Why? The benefit of steroids (less hearing loss and neurological damage) is shown for pneumococcal and Hib meningitis.
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Suspected bacterial meningitis outside hospital, with transfer likely to be delayed: what is given first?
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IM or IV benzylpenicillin or ceftriaxone.
Why? Early antibiotics save lives in meningococcal disease. They are not given if they would delay transfer or if there is a severe allergy.
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Cavernous sinus thrombosis: which cranial nerve is usually affected first, and why?
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Abducens (CN VI), because it runs through the middle of the sinus next to the internal carotid artery.
Why? CN III, IV, V1 and V2 lie in the lateral wall and are affected later. Infection from the "danger triangle" of the face is the classic cause.
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Which CSF protein supports a diagnosis of sporadic Creutzfeldt-Jakob disease?
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14-3-3 protein.
Why? It leaks from rapidly dying neurons. EEG periodic sharp-wave complexes and MRI changes also support sCJD.