Fact or fib? Blood-brain barrier, food allergy, TIAs and strokes
Vol.20, No.01, February 2012

Some of the clinical statements below are true, and some are not. Can you distinguish the facts from the fibs on the blood-brain barrier, food allergy, and TIAs and strokes? If you’d like to do another quiz try your hand at The PE Clinical Knowledge Contest. You could win an iPad 2.

1. The blood-brain barrier (BBB)

True / False

a) Is also sometimes called the blood-cerebrospinal fluid barrier.

b) Protects the entire brain from the main circulation of human blood.

c) The barrier is still immature and quite permeable in newborns.

d) The barrier stops most bacteria, but Borrelia, of Lyme disease, can physically burrow through it.

e) Inflammation of the meninges tends to decrease the permeability of the BBB still further.

f) In multiple sclerosis, an MS attack is a sure sign that the BBB is somewhere compromised.

g) In rabies, the virus mostly replicates in the brain, and the anti-viral immune cell can’t cross the BBB to get at it.


2. Food allergy

True False

a) About 2% of Canadians suffer from a food allergy, according to Health Canada.

b) Incidence is rising steadily.

c) People with peanut allergy have no extra risk of being allergic to other tree nuts.

d) People who have just used an epinephrine self-injector to control anaphylaxis should always go straight to by ambulance, even if their symptoms are controlled.

e) The EpiPen® and Twinject® auto-injectors are identical in terms of dosages and injection site.

f) When giving epinephrine, the patient should normally be on their back with legs slightly raised, but should lie on their side if nauseous or having trouble breathing.


3. In TIAs and strokes

True False

a) If symptoms of focal neurologic deficit resolve within 1 hour, the event is retrospectively diagnosed as ischemic attack.

b) Tissue plasminogen activators (tPA) are indicated early in acute ischemic stroke but not in TIAs.

c) Research shows that tPA is only effective if given in the first 3 hours of ischemic stroke symptoms, risks outweigh the benefits.

d) Silent strokes, asymptomatic attacks in which infarcts are incidentally detected later on MRI, are estimated symptomatic strokes by about 5 to 1.

e) About one stroke in 15 is hemorrhagic.

f) Many embolic obstructions don’t cause strokes because the Circle of Willis provides for redundancy between supplying arteries.


1. The blood-brain barrier: a) False, the blood-CSF barrier and blood-retinal barrier are similar but distinct; b) False, several areas of the brain are not behind the BBB, including the pineal gland; c) False, this early belief was due to too much osmotic pressure in early experiments. The BBB is well-developed in newborns; d) True; e) False, meningitis increases BBB permeability; f) True, otherwise lymphocytes would not be reaching myelin sheaths in the CNS; g) True.

2. Food allergy: a) False, about 4%; b) True; c) False, they’re at higher risk; d) True; e) True; f) False, they should sit up if having difficulty breathing.

3. In TIAs and strokes: a) False, it’s only a TIA if imaging shows no lasting damage; b) False, waiting to see which it is risks missing the treatment window for tPA; c) False, early research suggested a 3-hr limit, but later research showed benefit up to 4.5 hrs, which is now the protocol in Ontario hospitals; d) True; e) False, about 1 in 8 strokes is hemorrhagic; f) True.


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