Artificial Stone Silicosis Progresses After Exposure Stops

By Lisa Rappaport

June 29, 2020

(Reuters Health) - Progression of artificial stone silicosis continues even when patients stop working in the stone industry after diagnosis, a Spanish study suggests.

Researchers examined data on 106 men diagnosed with artificial stone silicosis between 2009 and 2018. Mean age at diagnosis was 36.2 years, mean duration of exposure was 12 years, and mean follow-up was 4 years.

At baseline, 99 patients (93.4%) had simple silicosis and seven patients (6.6%) had progressive massive fibrosis (PMF). By the end of the study period, a total of 40 patients (37.7%) had PMF.

"While classical silicosis in miners and quarries workers is decreasing in developed countries due to less activity and better protective measures, artificial stone silicosis is increasing," said lead study author Dr. Dr. Antonio Leon-Jimenez, head of pulmonology, allergy, and thoracic surgery at Puerta del Mar University Hospital in Cadiz, Spain.

Artificial stone has a lot more silica (90%) than natural stones like granite (30%) or marble (5%), Dr. Leon-Jimenez said by email. The artificial stones that have become more popular in kitchens and bathrooms also have more synthetic resins and metals.

"Workers that used to work with natural stone changed to these new materials, but with the same old protective measures," Dr. Leon-Jimenez said. "In this way, silicosis is highly probable."

During the study period, four patients died, two after lung transplants and two for causes unrelated to silicosis, the researchers report in Chest.

Silicosis was defined as International Labor Organization (ILO) category 1/0 or greater with a history of occupational exposure or by biopsy results and/or HRCT scans with a history of exposure, after excluding other diagnoses.

CXR progression in cases of increased profusion of small opacities in 2 or more subcategories, the presence of large opacities (A, B, or C), or an increase in the large opacities category. Progression was assessed in patients with at least 2 years of follow-up (N = 100).

At baseline, respiratory function tests showed mean forced vital capacity (FVC) of 86%. By the end of follow-up, mean FVC was 80.2%. Mean forced expiratory volume (FEV) was 86.6% at baseline and declined to 78.9% by the end of the study period.

Chest radiography showed 19 men in ILO category 0 at baseline, and only 3 men in ILO category 0 by final follow-up. Thirty-nine men were in ILO category 1 at the end of the study period, 24 men were in category 2, and 3 were in category 3.

"At this rate of progression, in a few years, a significant proportion of patients might develop respiratory failure and will need to undergo lung transplantation, the only effective treatment currently available for this disease," the study team writes.

Measures adopted to reduce the concentration of respirable dust, such as the use of water suppression and exhaust ventilation techniques, have been implemented, but harmful levels of dust are still documented in workplaces, generally in small factories, the authors note.

The investigators call for more aggressive engineering controls to prevent exposure, and for new treatments to be developed and tested.

One limitation of the study is that exposure levels of workers were only available in two factories, one where the level of free silica was within acceptable limits and one where the level exceeded these limits.

Even so, the results suggest that simply removing workers from exposure to silica will not be sufficient to prevent disease progression once they're diagnosed with artificial stone silicosis, said Dr. Robert Cohen, co-author of an editorial accompanying the study and a clinical professor of environmental and occupational health sciences at the University of Illinois at Chicago School of Public Health.

It is important to continue to follow them closely for disease progression, Dr. Cohen said by email.

"It also places more emphasis on primary prevention, lowering exposure to prevent the disease in the first place, because, if we wait until disease is diagnosed, they may still progress even if removed," Dr. Cohen said. Although some therapies are being tested, he added, “The disease is practically untreatable . . . once present, which makes prevention imperative.”

SOURCE: https://bit.ly/3eDPEkD and https://bit.ly/3i956Hp Chest, online June 18, 2020.

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