Progressive massive fibrosis

Progressive Massive Fibrosis is also known as Complex Pneumoconiosis. It is a disease that almost entirely affects coal miners. The disease arises firstly through the deposition of coal dust within the lung, and then through the body's immunological reactions to the dust. If disease is to be classified as PMF, the lung must contain lesions which are at least 1 cm in size, although some authorities place the boundary at 2 cm. In PMF, lesions most commonly occupy the upper lobes of the lung. Another characteristic of PMF lesions is that they are black.^[1] How factors cause disease is known as 'Pathogenesis'. The pathogenesis of PMF is complicated, but involves two main routes - an immunological route, and a mechanical route.

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Immunologically, disease is caused primarily through the activity of lung macrophages, which phagocytose dust particles after their deposition. These macrophages seek to eliminate the dust particle through either the mucociliary mechanism, or through lymphatic vessels which drain the lungs. Macrophages also produce an inflammatory mediator known as interleukin-1 (IL-1), which is part of the immune systems first line defenses against infecting particles. IL-1 is responsible for 'activation' of local vasculature, causing endothelial cells to express certain cell adhesion molecules, which help the cells of the bodies immune system to migrate into tissues. Macrophages exposed to dust have been shown to have markedly decreased chemotaxis. Production of inflammatory mediators - and the tissue damage that ensues as an effect of this, as well as reduced motility of cells, is fundamental to the pathogenesis of pneumoconiosis and the accompanying inflammation, fibrosis, and emphysema.

There are also some mechanical factors involved in the pathogenesis of Complex Pneumoconiosis that should be considered. The most notable indications are the fact that the disease tends to develop in the upper lobe of the lung - especially on the right, and its common occurrence in taller individuals.

References

Occupational Lung Diseases, 3rd Edition, Morgan and Seaton http://pim.medicine.dal.ca/il1.htm