Silicosis in artificial stone workers: Spectrum of radiological high‐resolution CT chest findings

Dose-response relationship between lung function and chest imaging response to silica exposures in artificial stone manufacturing workers

BACKGROUND

Occupational exposure to artificial stone, a popular material used for countertops, can cause accelerated silicosis, but the precise relationship between silica dose and disease development is unclear.

OBJECTIVES

This study evaluated the impact of silica exposure on lung function and chest imaging in artificial stone manufacturing workers.

METHODS

Questionnaire and spirometry assessments were administered to workers in two plants. A high-exposure subset underwent further evaluation, including chest CT and DLco. Weighting factors, assigned as proxies for silica exposure, were based on work tasks. Individual cumulative exposures were estimated using area concentration measurements and time spent in specific areas. Exposure-response associations were analyzed using linear and logistic regression models.

RESULTS

Among 65 participants, the mean cumulative silica exposure was 3.61 mg/m3-year (range 0.0001 to 44.4). Each 1 mg/m3-year increase was associated with a 0.46% reduction in FVC, a 0.45% reduction in FEV1, and increased lung function abnormality risk (aOR = 1.27, 95% CI = 1.03-1.56). Weighting factors correlated with cumulative exposures (Spearman correlation = 0.59, p < 0.0001), and weighted tenure was associated with lung function abnormalities (aOR = 1.04, 95% CI = 1.01-1.09). Of 37 high-exposure workers, 19 underwent chest CT, with 12 (63%) showing abnormal opacities. Combining respiratory symptoms, lung function, and chest X-ray achieved 91.7% sensitivity and 75% specificity for predicting chest CT abnormalities.

CONCLUSION

Lung function and chest CT abnormalities occur commonly in artificial stone workers. For high-exposure individuals, abnormalities on health screening could prompt further chest CT examination to facilitate early silicosis detection.

Preclinical Mouse Model of Silicosis

Silicosis is an untreatable occupational lung disease caused by chronic inhalation of crystalline silica. Cyclical release and reuptake of silica particles by macrophages and airway epithelial cells causes repeated tissue damage, characterized by widespread inflammation and progressive diffuse fibrosis. While inhalation is the main route of entry for silica particles in humans, most preclinical studies administer silica via the intratracheal route. In vivo mouse models of lung disease are valuable tools required to bridge the translational gap between in vitro cell culture and human disease. This chapter describes a mouse model of silicosis which mimics clinical features of human silicosis, as well as methods for intranasal instillation of silica and disease analysis. Lung tissue can be collected for histological assessment of silica particle distribution, inflammation, structural damage, and fibrosis in sections stained with hematoxylin and eosin or Masson's trichrome. This approach can be extended to other chronic fibrotic lung diseases where inhalation of small damaging particles such as pollutants causes irreversible disease.

Clinical efficacy of tetrandrine in artificial stone-associated silicosis: A retrospective cohort study

Background

Outbreaks of silicosis have occurred among workers in the artificial stone (AS) industry, and there is currently no effective antifibrosis treatment for silicosis.

Design

A retrospective cohort study.

Methods

We retrospectively analyzed the clinical data of 89 artificial stone-associated silicosis patients treated in Shanghai Pulmonary Hospital (China). Patients who agreed to be administered tetrandrine entered the observation group and those who disagreed entered the control group. Changes in chest HRCT, pulmonary function, and clinical symptoms of patients in two groups were compared pre- and post-treatment.

Results

After treatment for 3-12 months, 56.5%-65.4% of patients in the observation group showed improvements in HRCT imaging, while there was no improvement in the control group (p < 0.05). Disease progression occurred in 0%-17.4% of patients in the observation group after 3-12 months of treatment compared with 44.4%-92.0% of patients in the control group (p < 0.05). After 3 months of treatment, the forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), and diffusing capacity of the lung for carbon monoxide (DLco) in the observation group increased by 136.7 ± 189.2 mL (p < 0.05), 124.2 ± 169.9 mL (p < 0.05), and 1.4 ± 2.3 mL/min/mmHg (p > 0.05), respectively, while those in the control group decreased (145.8 ± 356.5; 107.5 ± 272.1; 1.9 ± 3.8). After 6 months of treatment, FVC, FEV₁, and DLco in the observation group increased by 207.8 ± 372.2 mL (p > 0.05), 107.8 ± 295.2 mL (p > 0.05) and 0.7 ± 6.0 mL/min/mmHg (p > 0.05), respectively, while those of the control group decreased (383.3 ± 536.7; 215.6 ± 228.9; 1.4 ± 1.7). The incidences of clinical symptoms such as cough, expectoration, dyspnea, chest tightness, and chest pain in the observation group were decreased-after treatment (all p < 0.05), while the incidences of these symptoms increased in the control group, although the change was not statistically significant (all p > 0.05).

Conclusion

Tetrandrine can control and delay the progression of AS-associated silicosis fibrosis, with improved chest HRCT imaging and pulmonary function.

Progressive massive fibrosis: An overview of the recent literature

This review provides an overview of literature addressing progressive massive fibrosis (PMF) from September 2009 to the present. Advances are described in understanding its pathophysiology, epidemiology of the occurrence of PMF and related conditions, the impact of PMF on pulmonary function, advances in imaging of PMF, and factors affecting progression of pneumoconiosis in dust-exposed workers to PMF. Basic advances in understanding the etiology of PMF are impeded by the lack of a well-accepted animal model for human PMF. Recent studies evaluating lung tissue samples and epidemiologic investigations support an important role for the silica component of coal mine dust in causing coal workers' pneumoconiosis and PMF in contemporary coal miners in the United States and for silica in causing silicosis and PMF in artificial stone workers throughout the world. Development of PMF is associated with substantial decline in pulmonary function relative to no disease or small opacity pneumoconiosis. In recent reports, computed tomography has had greater sensitivity for detecting PMF than chest x-ray. Magnetic resonance imaging shows promise in differentiating between PMF and lung cancer. Although PMF develops in dust-exposed workers without previously identified small opacity pneumoconiosis, the presence of small opacity pneumoconiosis increases the risk for progression to PMF, as does heavier dust exposure. Recent literature does not document any effective new treatments for PMF and new therapies to prevent and treat PMF are an important need.

Another One Fights the Dust - Targeting the NLRP3 Inflammasome for the Treatment of Silicosis

Silicosis is a multifaceted lung disease, characterised by persistent inflammation and structural remodelling. Despite its poor prognosis, there are no treatments currently available for patients with silicosis. Recent pre-clinical findings in models of lung fibrosis have suggested a major role for the nucleotide binding domain and leucine-rich repeat pyrin domain containing 3 (NLRP3) inflammasome in silica-driven inflammation and fibrosis. This review outlines the beneficial effects of targeting the NLRP3 inflammasome in in vitro cell experiments and in in vivo animal models, whereby inflammation and fibrosis are abrogated following NLRP3 inflammasome inhibition. While preclinical evidence is promising, studies which explore NLRP3 inflammasomes in the clinical setting are warranted. In particular, there is still a need to identify biomarkers which may be helpful for the early detection of silicosis and to fully elucidate mechanisms underlying these beneficial effects to further develop or repurpose existing anti-NLRP3 drugs as novel treatments that limit disease progression.

Silica Exposure Estimates in Artificial Stone Benchtop Fabrication and Adverse Respiratory Outcomes

Silicosis is being increasingly reported among young stonemasons in the artificial stone (AS) benchtop fabrication and installation industry. Respiratory health screening, which included a job and exposure history, a chest X-ray (CXR), a respiratory health questionnaire, and gas transfer testing, were offered to stonemasons in Victoria, Australia. Workers typically reported a variety of tasks, including cleaning and labouring, which made exposure assessment complex. We estimated the relative respirable crystalline silica exposure intensity of each job from the proportion of time using AS and the proportion of time doing dry work (work without water suppression). The relative average intensity of exposure for up to five jobs was calculated. Cumulative exposure was calculated as the sum of the duration multiplied by intensity for each job. Installers and factory machinists (other than computer numeric control operators) were the most likely to report dry work with AS, and so had a greater average intensity of exposure. Exposure intensity and cumulative exposure were associated with increased odds of an ILO (International Labour Organisation) CXR profusion major category of ≥1 and with dyspnoea. Exposure duration was also associated with ILO profusion category. In multivariate analyses of health outcomes, only job type was associated with the ILO profusion category. For both most recent and longest-duration job types, when compared to the lowest exposure group, factory machinists were more likely to have an ILO category ≥1. This suggests that intensity of exposure estimated from the proportion of time dry cutting and proportion of time working on AS can predict the risk of adverse respiratory outcomes for workers in this industry.

Artificial stone silicosis

PURPOSE OF REVIEW

This review details recent findings related to the health effects of occupational exposure to artificial stone dust and the rapid increase in cases of artificial stone associated silicosis around the world.

RECENT FINDINGS

High crystalline silica content artificial stone is now commonly used for the production of kitchen benchtops. Reports of artificial stone silicosis from many countries have noted that workers were typically employed at small workplaces and were often diagnosed in their 30s or 40s. Poor exposure control measures were common, including the practice of 'dry processing'. Dust generated from artificial stone has been noted to have properties that influence toxicity, including high silica content, generation of nanosized particles and presence of metals and resins. Artificial stone silicosis differs from silicosis associated with other occupational settings including shorter latency and rapid disease progression. High-resolution computed tomography (CT) chest imaging of artificial stone silicosis has often noted the presence of ground glass opacities, which may not be detected in chest x-ray screening. Increased prevalence of autoimmune disease, such as scleroderma, has also been reported in this industry.

SUMMARY

Further evaluation of the safety of work with artificial stone is required, including the effectiveness of dust control measures. Current reports of artificial stone silicosis indicate the potential for widespread undiagnosed respiratory disease in this industry. Provision of more sensitive health screening methods for all at-risk workers and the development of new treatment options particularly for this form of silicosis is urgently required.