- What does the chest radiograph show in image 2.1?
There are confluent nodules that fill much of the lung volume.
- Describe what you see in images 2.2 and 2.3. What is the probable
diagnosis?
The lesion consists of concentric whirled bundles of hyalinized collagen fibers with scattered black pigment. The pattern is usually random, with some nodules located in perivascular or peribronchiolar location, and others scattered within the lung parenchyma. The lesion in image 2.2 is viewed under polarized light, and demonstrates numerous polarizable crystals. This is a characteristic picture of silicosis.
- How does this lesion form? What are the offending particles
seen in image 2.2?
The lesion forms in reaction to cellular damage thought to be caused by interaction between SiOH groups on the hydrated surface of the silica crystals, the offending particles, with cellular macromolecules in macrophages, including phospholipids and proteins. There is damage to lipid membranes, with cell injury and death leading to release of a soluble protein factor that stimulates fibroblast proliferation and collagen synthesis.
- How do you explain the lengthy hiatus between exposure and
symptomatology?
Silicosis is a chronic disease that does not manifest itself
clinically until 20-40 years after the initial exposure. The reason can be seen by examining the pattern of injury, and realizing that initially the hyalinized
nodules will be tiny and insignificant, but that cellular injury continues with ongoing increasing fibrosis and collagen deposition until eventually enough normal lung is damaged to cause symptoms. This ongoing damage does not require continued exposure, rather the residual crystals in the lung cause the continued damage.
- These patients are at high risk for developing what disease?
Tuberculosis. Patients with silicosis have impaired resistance to tubercle bacilli, possibly on the basis of silica-induced injury to macrophages. 0.5 to 5.0% of all cases of silicosis contract TB, and up to 60% of patients with conglomerate silicosis become infected.
- In a patient with a more severe form of this disease, what are factors that would contribute to hypoxemia with exercise? What factors may contribute to a high ventilation rate during exercise in a patient with diffuses interstitial pulmonary fibrosis?
Hypoxemia would be exacerbated by the reduced time the blood spent in the pulmonary capillaries and by ventilation/perfusion (V/Q) abnormalities.
Hypoxic stimulation of peripheral chemoreceptors will occur.
- What recourse does a patient have when the disease is a consequence of employment?
Silicosis is a classic example of environmental medicine. Thousands of people have died from silicosis, and most worked for mining or construction-related industries. They won damages when lawyers were able to show that employers did their best to hide information about the health effects of their workplace and didn't clean them up because of the expense.
Can doctors ever applaud the outcome of a lawsuit for a patient? Sometimes innocent people really are harmed who should not have been (i.e. someone or some organization knew better and failed to live up to their responsibilities). Is the goal of business only to make a profit? If a business goes into bankuptcy from lawsuits, what is the cost to society? When do people become expendable? If these ideas are taught in business school, or if society demands business practice standards which must be met, future businessmen will be more likely not to make the same mistakes.
