Silicosis
is a disease entity that results from chronic, sometimes 10 to 20
years, of crystalline silica exposure. Those in occupations such as
mining, quarrying, sandblasting, road building, stone polishing, are
susceptible to silica exposure. The immunologic response to inhaled
silica is the formation of numerous pulmonary nodularities composed
of concentric rings of collagen. In chronic simple silicosis,
exposure to years of silica results in marked radiological changes,
but often with little clinical symptoms or changes in lung
function.
In acute silicosis, a relatively short exposure to silica results
in severe pulmonary dysfunction, and is fatal in months to years.
Complicated silicosis may occur from the progression of simple
silicosis, with resulting progressive massive fibrosis. It is
characterized by large conglomeration of the numerous micronodules
into masses greater than 1 cm. It invariably leads to decrease
pulmonary function, resulting in arterial desaturation and
eventually cor pulmonale. The degree of pulmonary involvement can
be graded with the ILO International Classification of Radiographs
of Pneumoconioses.
Symptoms
There are no symptoms in the early stage. Later the initial
complaint is of a dry morning cough. Next occurs some
breathlessness, at first noticeable on exercise but, as destruction
of the lung tissue proceeds, breathlessness worsens until it is
present at rest. The interval between exposure and the onset of
symptoms varies from a few months in some susceptible individuals
to, more usually, many years, depending on the concentration of
respirable free silica and the exposure time at work. Silicosis is
the one form of pneumoconiosis that predisposes tuberculosis, when
additional symptoms of fever, loss of weight, bloody sputum may
occur. In the presence of gross lung destruction the blood
circulation from the heart to the lung may be embarrassed and result
in heart failure.
Workers in many industries and occupations are at risk,
including:
Construction, especially bridge, tunnel, and elevated highway
Wrecking and demolition
Concrete work
Surface mining and quarrying
Underground mining
Stone cutting
Milling stone
Agriculture
Foundry
Ceramics, clay, pottery
Vitreous enameling of china plumbing fixtures
Glass manufacturing
Manufacturing of concrete products and brick
Manufacturing of soaps and detergents
Shipyards, railroads
Other employees who do not work directly with materials containing
silica may be exposed as bystanders if they are in the area when
crystalline silica containing materials are being used.
Materials Containing Crystalline Silica
Granite and marble
Quartz and quartzite
Sand, gravel, and sandstone
Slate and Traprock
Many abrasives used for abrasive blasting
Concrete, concrete block, cement
Brick and refractory brick
Mortar
Gunite
Soil, especially sandy soil
Asphalt containing rock or stone
Radiologic Overview:
In simple silicosis, radiographs show numerous tiny round
pulmonary nodules of uniform size, with a upper lung predominance.
There may be a reticular, nodular, or reticulonodular pattern of
opacities. On CT there may be thicken inter and intralobular bands
with ground glass opacities.
With progression of the disease, there is coalescence of the
nodules into larges masses. Mediastinal and hilar adenopathy can
also be present. Characteristic peripheral eggshell calcification
of the lymph nodes occurs in approximately 5% of the patients. With
progressive massive fibrosis, there is retraction of the lung
centrally with the formation of emphysematous changes at the
periphery.
Key points:
- There is an upper lung predominance of nodules in silicosis
- Eggshell calcification of lymph nodes occur in 5% of cases
