Læknablaðið - 15.03.1980, Qupperneq 5

LÆKNABLADID
39
tory failure. There is no specific treatment and
corticosteroids are useless.
Pleural plaques may develop before or
after the distinctive radiographic pattern of
asbestosis is apparent. They are detected by
examining carefully the posteroanterior chest
radiograph for thickening of the pleura. When
pleural fibrosis is well advanced, calcification
is frequent; the diaphragms are common site
and bilateral diaphragmatic calcification is
practically diagnostic of asbestos or similar
fibrous mineral disease. It is unlikely that
pleural thickening or calcification develop
without diffuse asbestosis. However, this is not
always apparent from the radiograph. When
plaques are extensive there may be functional
impairment with a pattern of reduced lung
volumes and reduced tolerance for exercise
and dyspnea even on mild exertion. In a few
instances decortication of the pleura has
ameliorated the dyspnea although measure-
ments of pulmonary function have shown little
change.
Mesothelioma is an unusual neoplasm
which was rarely described until well into this
century and then almost always associated
with prior exposure to asbestos. Among hea-
vily exposed asbestos production or insulation
workers, peritoneal and pleural mesothelio-
mas are about equally common. causing death
of about 8 % of these groups. Ascites and
increased abdominal girth may be the initial
sign of the peritoneal tumor while chest pain
and an irregular cauliflower pleural mass on
radiograph distinguish the pleural one. Biopsy
is needed to confirm the diagnosis. It reveals a
mixture of monotonous cells with large nuclei
which may be arranged in acini and of
fibrocytes. Survival after diagnosis is rarely
longer than one year. Although chemotherapy
using combinations of drugs may extend life,
their effect rarely lasts longer than a few
months.
The least specific but most frequent lethal
disorder in asbestos workers is lung cancer
which accounts for up to 60 % of deaths. The
frequency is only 2-4 times expected rates in
non-smokers of cigarettes but is approximate-
ly 8 to 10 times increased above the already 10
fold increased rate in those who smoke.
Although adenocarcinomas are increased, the
majority of the turnors are squamous cell or
undifferentiated. Except for the signs of other
associated asbestos disease there are no speci-
fic findings which are different from other
patients with lung cancer. Finally, cancer of
the colon is clearly increased in asbestos
exposed groups as is laryngeal cancer. Both
are important and show synergistic effects
with cigarette smoking although the rates are
much below those for lung cancer. The impor-
tant principles which emerge from almost 50
years of experience with asbestos disease are
listed and then described below. They apply
with some adaption to other environmental
disorders.
1. There is long latent (asymptomatic) period
between the initial exposure and detection
of disease. This depends somewhat on the
dose; ranging from 10 to 40 years.
2. Disease is usually well advanced when it is
detected. This is typical of disorders due to
fibrosis as well as to neoplasms.
3. There are often co-factors which add or
synergize to produce more serious disease.
Cigarette smoke exposure is synergistic
with asbestos to greatly increase the fre-
quency of lung cancer.
4. Exposure need not be direct — there is
bystander’s effect from sharing the airmass
at work or contaminating the home. Thus,
family members of asbestos workers have
developed mesotheliomas and typical fi-
brosis by radiograph without having any
direct occupational exposure to asbestos.
5. There appears to be no threshold for
neoplasms caused by asbestos.
6. The diseases are essentially irremedial
when whey are detected. It follows from
this that the only effective strategy is to
prevent exposure.
The world’s use of asbestos is approximately
5,7 million tons per year. Production is center-
ed in the USSR, Canada and South Africa with
less in Finland and USA. Use is largely in
Europe and America. Almost 80 % of asbestos
is used in construction and building materials
for heat, insulation or strengthening com-
pounded materials. Substitutes are available
for most of these uses. Friction-heat uses as in
vehicle brakes and fire resistent suits take
about 10% and there are not as yet any
durable substitutes.
The ntineral is mined in clumps or cobbs of
fibers. These are broken out and separated by
fiber length. It is a complex magnesium silicate