Deposition of coal dust in the lungs can lead to lung disease. Coal mining is the major source of exposure. The tissue reaction to coal dust inhalation is the development of a coal macule. Focal emphysema can form around the macule. This combination is termed a coal nodule and is the characteristic lesion of simple coal worker's pneumoconiosis (CWP). In addition to CWP, coal dust exposure is also related to the development of airflow limitation, chronic bronchitis, and emphysema. Silica exposure often occurs in combination with coal dust exposure; thus, the previously described silica-related illness might also be seen.^1,3

Simple CWP is usually without symptoms. Shortness of breath or a productive cough is often related to chronic bronchitis or airflow obstruction. Progressive massive fibrosis (PMF) can occur, more commonly when there has also been exposure to silica. Symptoms advance as the PMF worsens (Fig. 6). Deaths from CWP continue to occur (Fig. 7).

Given the common absence of symptoms, simple CWP is often a radiographic diagnosis. Chest imaging reveals small nodules with upper and posterior zone predominance. Hilar lymph node enlargement is not uncommon, although eggshell calcification does not generally occur. When PMF occurs, these small nodules coalesce, forming opacities larger than 1 cm. These lesions are odd-shaped, usually bilateral, and progressive, and they can cavitate or become calcified. Care must be taken because lesions diagnosed radiographically as PMF are often shown later to have been tumors, tuberculosis scars, or Caplan's nodules (see later).

Simple CWP tends to have little effect on lung function. Airflow limitation, restriction, and a reduction in diffusing capacity can all be seen when PMF develops. Pulmonary hypertension can develop in advanced disease.

Complications of CWP include a higher incidence of mycobacterial disease (although not as high as with silicosis), and an increased risk of stomach cancer. Tuberculin skin testing, chemoprophylaxis, and treatment of active tuberculosis are as recommended in silicosis. Caplan's syndrome is a nodular form of CWP seen in persons with rheumatoid arthritis. The nodules are multiple, tend to be larger than typical coal nodules, develop over short periods of time, and cavitate more often. These findings usually occur concomitantly with the joint manifestations, active arthritis, and the presence of circulating rheumatoid factor.