Page 49 - AlertDiver_Spring2013
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divers compared to nondiving controls (Erdem et al., 2009). A
positive correlation, however, does not always imply causation.
Most of these studies (including ours) did not establish any
significant relationship between white-matter lesions and
diving indices. Even if divers had increased numbers of white-
matter lesions, their clinical relevance and association with
neuropsychological symptoms has not yet been clearly defined.
Kay Tetzlaff:
There is an abundance of studies that investigated
MRI in a variety of diving cohorts, and many of these reported
associations between parameters of diving exposure and
presence of brain lesions on MRI. However, none could actually
prove a causal relationship. A fundamental flaw in study design
has been the possibility of a selection bias, in that the lesions
in the selected divers could have been pre-existing. In fact, the
studies could not disprove a hypothesis that the decision to start
diving may be the first sign of brain damage. One way to reduce
bias would be a longitudinal follow-up of a cohort of divers from
the beginning of their diving career compared to a cohort of
nondivers while controlling for confounding risk factors such as
alcohol intake, smoking, hypertension and others. Such a study
has yet to be reported.
What is the relationship between a PFO and
brain lesions?
Moon:
There is a weak relationship between the presence
of a PFO and the presence of these lesions. But again, there
is no evidence that these lesions indicate brain damage.
Uzun
: So-called “silent gas bubbles,”
which may be detected even after
dives in shallow water, do not
produce clinical symptoms and
are generally filtered through the
pulmonary vasculature. A PFO,
an opening between the right
and left atria, may serve as an
entry point for silent gas bubbles
into the arterial circulation. It is
hypothesized that these bubbles
can interrupt small vessels in the
brain and cause white-matter
brain lesions. Indeed, a number of
studies demonstrated that divers
with a PFO had an increased risk
for white-matter lesions compared
to divers without a PFO. There is
no general recommendation that
asymptomatic scuba divers should
undergo examinations for PFO detection. However, a diver
with a known PFO should use a conservative dive profile to
reduce the risk of DCS.
Tetzlaff:
A PFO increases the risk of decompression illness
(DCI) and thereby may also enhance brain lesions on MRI.
It has been estimated from a clinical study that divers with
a PFO have a 4.5-fold increase in DCI events and twice
the incidence of ischemic brain lesions compared to divers
without a PFO (Schwerzmann M et al., 2001). However, it
should be noted that diving even with a PFO is considered
safe when dives are performed according to guidelines.
Note that it is not the PFO that causes injury but the
presence of gas bubbles during or after the dive. The bubble
load can be minimized by avoiding risk factors such as deep
dives, cold dives and decompression dives.
What are other possible mechanisms of formation
of the brain lesions known as white spots?
Moon:
They could be related to normal aging processes such
as changes in blood vessels.
Uzun:
White spots of the brain observed on MRI are
actually common in elderly people and may be associated
with head injuries, alcohol consumption, migraines, smoking,
hypertension and/or high blood cholesterol. It is generally
accepted that white-matter lesions represent parenchymal
damage due to cerebrovascular disorders or cerebral ischemia.
Tetzlaff:
White-matter hyper
intensities are regarded as typical MRI
expressions of cerebral small-vessel
disease. Pathological correlates are
varied with most pointing toward
white-matter hyperintensities as a
reflection of small-vessel ischemic
burden. The predominant clinical
associations are with stroke,
cognitive impairment and dementia.
The prevalence of white-matter
hyperintensities increases with age.
What is the relationship between
reduced neuropsychological
performance and the presence of
brain lesions?
Moon:
So far, no one has demonstrated
any such relationship in divers.
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Tests such as the Montreal Cognitive
Assessment help researchers detect mild
neurological impairment.
STEPHEN FRINK
