Pleural Mesothelioma The incidence of pleural mesothelioma will probably increase into the next century. A complete occupational history should include an inquiry about asbestos exposure, especially in patients with chest pain or dyspnea. The latency period between exposure and mesothelioma is as long as 50 years. In some patients, early diagnosis leads to a chance of cure. In most cases, however, there is no cure. Accurate diagnosis and a frank discussion of prognosis will allow patients to prepare for death. Pleural mesothelioma is a mesenchymal tumor that occurs primarily in the pleura (80 percent of cases) or the peritoneum (20 percent of cases).(1) First described in 1870, the association between mesothelioma and asbestos was not convincingly documented until 1960, when high tumor rates were found in South African asbestos miners.(2)
Mesothelioma is a rare tumor, with an incidence rate of one to two cases per 1 million persons per year. In some asbestos-exposed groups, however, mesothelioma accounts for 10 percent of all deaths.(3)
Early diagnosis is crucial for any hope of cure. Even in typical cases where cure is impossible, the diagnosis is important so that patients can prepare for death, both psychologically and practically.
Epidemiology
The term "asbestos" refers to any of a group of naturally occurring fibrous silicates, mainly crocidolite (blue asbestos, mined in South Africa), chrysotile (white asbestos, mined in Canada, the United States and the Soviet Union), amosite (brown asbestos, mined in South Africa) and anthophyllite (mined in Finland).
Exposure to asbestos is the number one risk factor for malignant mesothelioma. Of the types of asbestos, crocidolite is by far the most dangerous, followed by amosite and chrysotile.(4,5)
There is a latency period of 20 to 50 years between asbestos exposure and the development of mesothelioma. It was estimated that the incidence of mesothelioma would peak in the late 1980s, because of the heavy asbestos use in the shipbuilding industry during World War II.(6) Two considerations make it appear likely that the incidence of mesothelioma will continue to rise into the early twenty-first century.(7)
First, the safe level of asbestos exposure is unknown. Most risk estimates are extrapolated from studies of heavily exposed individuals.(8) The relevance of these data to lightly exposed persons is unclear. Most urban dwellers have some asbestos fibers in their lungs.(9) Family members of asbestos workers have developed mesothelioma,(10) as have persons living in the vicinity of asbestos plants.(11) Some cases of mesothelioma have been reported in persons who were exposed to asbestos for a period as short as two days.(12)
The uncertainty over safe levels of asbestos exposure is illustrated by recent government actions. In June 1987, the Occupational Safety and Health Administration lowered permissible exposure levels from less than 2 fibers per cubic centimeter of air to less than .01 fibers per cubic centimeter of air. The Environmental Protection Agency is considering a total ban on asbestos.(13) There is, apparently, no proven safe threshold level.(14)
The second reason for the growing incidence of mesothelioma is the fact that asbestos is still widely used in manufacturing and industry in the United States. Its strength and superior qualities of heat, acid and sound resistance make it an attractive industrial material. Asbestos is a component of concrete, asphalt, tile, industrial water filters, brake linings, clutch linings, pipes, paints, steam pipe insulation and electric wire insulation. Crocidolite, the most dangerous asbestos, is the fiber of choice for large-diameter pressure pipes. Although asbestos is usually bound inertly in these products, fabrication or use of the products often entails drilling or cutting the material, liberating dangerous asbestos dust in the process. Many workers in the construction and manufacturing industries continue to be exposed to asbestos.
Clinical Features
Chest pain and dyspnea are the most common symptoms of pleural mesothelioma.(15,16) The chest pain is characteristically nonpleuritic and varies in intensity from mild to incapacitating. Constitutional symptoms such as fever, weight loss and weakness are not uncommon. Despite the proven link between asbestos and mesothelioma, fewer than 50 percent of studied patients relate a definite history of asbestos exposure. This low figure may simply be a matter of inaccurate histories in persons with a disease that has a 20- to 50-year latency period or may reflect exposure to various dusts or chemicals presently unrecognized as etiologic factors, unrecognized incidental exposure or other etiologic mechanisms.
Physical findings are usually those of an underlying pleural effusion, which is present in more than 50 percent of cases at diagnosis. Other specific physical findings are usually lacking. The tumor may spread through the thoracic wall, producing subcutaneous nodules, but distant metastasis is unusual at the time of initial diagnosis, and such a finding suggests another type of tumor. In about 25 percent of patients, hematogenous metastasis to other organs will develop during the course of the disease.(17)
Chest radiographs are rarely normal in patients with mesothelioma. Findings include pleural effusion, pleural thickening, pericardial effusion, a mediastinal or chest wall mass, and pulmonary nodules.
Diagnosis is confirmed by tissue examination. In the presence of pleural effusion, about 30 percent of aspirated specimens of pleural fluid are positive for malignant cells. Pleural biopsy of the involved area is positive in about one-half of the cases and shows atypical cells in another one-third. If aspiration and needle biopsy of the pleura are negative, open thoracotomy with biopsy should be considered.
Patients with pleural mesothelioma require a multidisciplinary treatment approach, which may include surgery, radiation therapy and chemotherapy. Median survival is 12 months; only 5 percent of patients survive five years, although early diagnosis and treatment may occasionally lead to cure. Aggressive combination therapy has been reported to prolong survival, but such studies did not address quality-of-life issues, and the findings have not been uniformly confirmed.(18) The family physician's main task is usually to coordinate palliative therapy, assure pain control and provide psychologic support for patients and their families.
Illustrative Case
A 75-year-old man complained of constant upper-left lateral thoracic pain. He said he had fallen from his bicycle shortly before the onset of symptoms and attributed the pain to the fall. Physical examination was unrevealing. Rib films showed no abnormality, and he was treated with aspirin. When he was seen again one month later, the pain had not abated. His medication was changed to ibuprofen, again without total relief. A chest film at this time was normal.
For the next six months, the pain waxed and waned but was generally tolerable. The patient did not lose weight and, aside from weakness and mild dyspnea, did not complain of other symptoms. When the pain suddenly worsened, another chest film was taken, which showed a pleural mass and effusion in the upper left thorax At this point, the patient revealed that in 1937, he had been employed for 30 days as a lathe operator working on high-pressure pipes that contained asbestos. Pleural biopsy confirmed the diagnosis of mesothelioma.
Because of a recent myocardial infarction and worsening coronary artery disease, he was not a surgical candidate. Faced with the diagnosis, the patient entered a prolonged period of denial. A family conference was held, and the diagnosis, prognosis and practical options open to the patient were frankly discussed. When the patient accepted the diagnosis and the inevitability of death, he executed a durable power of attorney for health care, completed a will and made other financial decisions important to his family. He chose not to undergo chemotherapy or radiation therapy.
The patient's care was managed at home with the assistance of visiting hospice nurses and family counseling. He died three and one-half months after the diagnosis of mesothelioma was made.
This case illustrates several of the characteristics of mesothelioma. The patient was exposed to asbestos for only a brief period, and there was a long interval between exposure and the development of mesothelioma. Since the patient was working with high-pressure pipes, he was probably exposed to crocidolite. Initial symptoms were chest pain and dyspnea. The diagnosis was suggested by an abnormal chest radiograph, and the clinical course was rapidly fatal.
Pleural mesothelioma is an aggressive cancer. Early diagnosis can sometimes lead to a cure, but in most patients, diagnosis is important for allowing the patient to prepare for death. In the illustrative case, the patient was able to use his remaining period of competency to complete various legal and financial tasks. Failure to make a definitive diagnosis, combined with the patient's denial, could have imposed substantial legal, psychologic and financial burdens on the family as the patient's condition deteriorated.
PHOTO : Chest film showing pleural-based masses in the left upper chest and a left pleural
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