| 1. |
How
can cardiac MRI assess myocardial ischemia?
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Cardiac MRI
provides information on cardiac anatomy and function. It gives information
on any reversible ischemia and presence of myocardial infarction. It may
assess myocardial ischemia through two approaches: adenosine perfusion
stress MRI and dobutamine stress MRI. With perfusion stress, adenosine
is infused intravenously into the circulation, followed by injection of
gadolinium as a contrast agent. Adenosine is a potent vasodilator but
stenosed coronary arteries would be less dilated than normal coronary
arteries. Therefore, a preferential shunting of contrast agent would be
noted in the myocardium supplied by normal coronaries, leaving a perfusion
defect in the myocardium supplied by the diseased coronary arteries. With
dobutamine stress MRI, dobutamine, which is a potent inotrope, will be
infused in incremental dosages intravenously. Ischemic myocardium will
experience an initial increase in contractility, followed by a decrease
in contractility in high doses. Areas of myocardial infarction may be
detected by the late enhancement technique, with which gadolinium is injected
intravenously, followed by acquisition of images 15 minutes later. As
infarcted myocardium clears off the contrast agent much slower than normal
myocardium, the infarcted territories will be 'stained' with the bright
contrast agent.
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Figure 1: Areas
of myocardial ischemia are shown up as 'dark' perfusion defects.
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| Figure 2: Multiple
areas of myocardial infarcts are shown up as 'bright' tissue |
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| 2. |
What
are the risks of cardiac MRI?
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Cardiac MRI
is a safe procedure. The incidence of major risk is smaller than 0.1%
and is mainly associated with side effects of drugs. Adenosine may cause
bronchospasm and heart block while dobutamine may cause arrhythmias.
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| 3. |
What
are the accuracies of cardiac MRI? |
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In most series,
the sensitivity and specificity of cardiac MRI in diagnosing myocardial
ischemia are more than 90%. For diagnosing infarcted myocardial tissues,
its accuracy is comparable to, if not higher than that of nuclear techniques
such as thallium stress or PET scan.
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| 4. |
What
preparations are needed before cardiac MRI? |
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24 hours before
the procedure, the patient should refrain from caffeine intake (such as
tea, coffee, chocolate and soft drinks), nitrates and beta-blockers (for
dobutamine stress test). |
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| 5. |
What
are the contraindications for cardiac MRI? |
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The usual contraindications
for MRI will be observed (such as metallic implants, presence of pacemakers
etc). In addition, stress MRI is contraindicated in unstable scenario such
as acute coronary syndrome, uncontrolled hypertension, complex arrhythmias,
obstructive cardiac lesions, active asthma/COPD and significant AV block. |
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| 1. |
What
is the diagnosis?
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The clinical
diagnosis is cutaneous larva migrans, also known as creeping eruption.
It is a caused by percutaneous penetration and migration of hookworm larvae
(such as the Ancylostoma and necator species) that usually infest cats,
dogs and other animals. The characteristic clinical picture is that of
itchy erythematous rash arranged in serpinginous, sinuous or linear pattern
due to the moving parasites.
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| 2. |
Is
laboratory investigation(s) necessary to confirm the diagnosis?
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Clinical appearance
is characteristic and diagnostic skin biopsy is rarely needed.
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| 3. |
What
are the other common sites of involvement?
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People of
all ages can be affected if they have been exposed to the larvae which
are present in warm, moist, sandy soil. Common sites of involvement include
the feet, hands and buttocks.
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| 4. |
Who
are at risks of developing this condition?
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People at
risk include barefoot beachgoers and sunbather, farmers, gardeners, pest
controllers, and people playing in sandpits.
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| 5. |
What
are the treatment options for this disease?
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Cutaneous
larva migrans is self-limiting because human is a ‘dead-end host’. Most
lesions will resolve within 1-3 months. However, treatment is usually
necessary because it is symptomatic and nobody will like to have moving
parasites under their skin. There are topical, systemic and locally destructive
therapy. Topical therapy usually takes the form of 10-15% thiabendazole
cream applied twice daily for 5-10 days. Systemic therapy include oral
albendazole (for a 3-5 days course) or a single dose of ivermectin. Cryotherapy
using liquid nitrogen can be tried but whether all the larvae can be killed
by freezing is debatable.
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