Pneumoconiosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

Pneumoconiosis is an occupational lung disease caused by the inhalation of dust. Depending on the type of dust, variants of the disease are considered. Frequent types are asbestosis, coal miner’s lung, silicosis, and berylliosis. Rare types include siderosis, byssinosis, and talcosis. ^[1] Pneumoconiosis involve the particles causing irreversible lung damage and there is heavy emphasis on prevention through safety precautions at workplace settings. ^[2] To be qualified as a Pneumoconiosis or occupational disease there must be four criteria met. This includes documented exposure to the particle, a latent period before the development of symptoms, clinical signs and symptoms that entail the disease, and finally exclusion of other disease modalities. ^[3] There is no cure for the diseases and patients generally enter pulmonary rehabilitation programs and can become candidates for transplants during the end stages. ^{[4] [5]}

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

Because the various pneumoconiosis present after exposure to specific particles and dust, their historical perspective varies according to the antigen. Generally, once patients began to present following exposure to a particle, safety measures and awareness followed.

• There is evidence in ancient Egypt and Greece for a disease caused by silica inhalation. ^[1][2]
• Berylliosis was coined in 1946, when fluorescent lamp workers began presenting with pulmonary granulomatous diseases. ^[3]

• Many countries have banned the use of asbestosis and the United States has significantly decreased its use since the 1970s. ^[4]
• The UK limited its use of silica since 1949. ^[5]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

Pneumoconiosis may be classified according to subtypes based on the particle of exposure. These can be fibrogenic, granulomatous, benign or hard metal: ^{[1] [2]}

• Fibrogenic: silica, coal, asbestos, talc
• Granulomatous: beryllium
• Benign: Iron, tin, barium
• Hard metal: cobalt

• Fibrogenic:
  • Silicosis – silica
  • Coalworker’s pneumoconiosis
  • Asbestosis – asbestos fibers
  • Talcosis – talc
• Granulomatous:
  • Berylliosis – beryllium dust
• Benign:
  • Siderosis – iron
• Hard metal pneumoconiosis

Pneumoconiosis in combination with multiple pulmonary rheumatoid nodules in rheumatoid arthritis patients is known as Caplan’s syndrome.^{[3] [4] [5]}

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Karol Gema Hernández, M.D. [2], Dushka Riaz, MD

Pneumoconiosis is an interstitial lung disease caused by the accumulation of different dust particles in the alveolar space. As the particles accumulate, the body’s elimination mechanisms begin to fail, resulting in activation of chemotactic factors that exacerbate the inflammatory response, and subsequently leading to fibrosis. ^[1]

The pathogenesis of pneumoconiosis starts with the inhalation of mineral, metallic or dust particles. The most common particles that cause pneumoconiosis are:

• Asbestos ^[2]

• Silica (quartz, cristobalite, coesite or tridymite silica polymorphs)
  • Structural differences between the polymorphs of silica, are important because of the different degrees of biological reactivity they present, making some of them more toxic than others. The biological reactivity makes quartz more toxic, followed by tridymite, cristobalite, coesite, and finally stishovite. ^{[3] [4] [5]}

• Coal

Other dust particles may also lead to pneumoconiosis, such as hydrated magnesium silicate, hydrous aluminum silicate, bauxite, cobalt, beryllium and iron. ^{[6] [7]}

Each dust particle has a different degree of biological reactivity. The dust particles ultimately cause inflammation, fibrosis and finally, irreversible lung disease. ^[1] This variability is due to properties in the surface of the particles. In the case of silica, there are two theories explaining their biological reactivity. One of them is that silica is a hydrogen donor, whereas biological macromolecules are hydrogen acceptors, creating strong hydrogen bonds that contribute to the damage. The other theory is that at a pH of 7.0 ^[3], silica is negatively charged, and therefore attracting alveolar macrophages, and activating the generation of reactive oxygen species and cytokines.

Shown below is a table summarizing the dust exposure associated with pneumoconiosis.

When particles reach the distal lung, the mucociliary and lymphatic system take care of their elimination. Dust fibers must be less than 3 μm in diameter in order to penetrate the distal lung. Fibers greater than 5 μm are phagocytosed incompletely and retained in tissues. When particles increase in number, macrophages are activated to engulf those particles. Reticulin is then secreted by fibroblasts to entrap macrophages, as an attempt to control the excess of dust particles. ^[8]

The physiology of macrophage activation is subject to several theories. The macrophages are mainly derived from peripheral blood monocytes and, from local replication. The recruitment of monocytes from peripheral blood occurs in response to several chemotactic factors. Boitelle et al ^[9] suggest that one of the most potent chemotactic factors for peripheral blood monocytes is monocyte chemoattractant protein- 1 (MCP- 1), suggesting its role in chronic macrophage inflammation. TNFα activates MCP- 1 expression. MCP-1 is a 76 amino acid peptide that activates monocytes, and also increases its cytostatic activity and the expression of monocyte adhesion molecules such as CD11c/CD18 and CD11b/CD18.

As exposure continues, the elimination system begins to fail, leading to release of reactive oxygen species. These in turn exacerbates the inflammatory response, with the release of more cytokines, such as TNF and interleukins, which subsequently lead to fibrogenesis.

The determinants for the rate of disease progression are the accumulative dose; that is based in duration and intensity of exposure, the fiber type and individual susceptibility.

The underlying pathogenic mechanisms that lead to pulmonary fibrosis in pneumoconiosis remain unclear. Some studies in bronchoalveolar lavage made by Vanhée et al ^[10] suggest a potential protective effect of TGF- β on the development of pulmonary fibrosis. The alveolar macrophages in coal miners with massive fibrosis, secreted two main profibrotic factors; platelet-derived growth factor (PDGF) and insulin-like growth factor– 1 (IGF-1), whereas, the patients with simple pneumoconiosis secreted transforming- growth factor- β (TGF– β). This suggested a potential protective effect of TGF– β against the development of pulmonary fibrosis.

The risk for pneumoconiosis among constructions workers is evident, but Tjoe et al concluded there is not a clear-cut relationship between exposure and body’s response. This is complex due to the heterogeneity in exposure levels, as well as dust composition and the possible modification of toxicity by other factors present in dust.^[11]

Shown below is an image depicting a lung affected with pneumoconiosis.

Pneumoconiosis is caused by environmental exposure. However, acute and more severe forms of the disease do develop in more genetically susceptible people. For example, a study found polymorphism in IL‐1RA (+ 2018) may increase the risk for the development of silicosis. ^[12]

Conditions associated with pneumoconiosis include: ^[13]

• Asbestosis can cause malignant mesothelioma and bronchogenic carcinoma.
• Silicosis can exacerbate carcinoma and tuberculosis.
• Coal worker’s pneumoconiosis can increase the risk of tuberculosis.

On gross pathology, pleural plaques are characteristic findings of asbestosis as well as diffuse interstitial pulmonary fibrosis in reticular formation. Coal worker’s pneumoconiosis and silicosis both show small interstitial nodules in the upper lung. All pneumoconiosis will present with chronic fibrosis. Silicosis may include eggshell dystrophic calcification. ^[14]

On microscopic histopathological analysis, anthrocytes, or dust-laden macrophages are characteristic findings of coal worker’s pneumoconiosis. Onion skin lesions with concentrically arranged fibers and a central acellular area are typical of silicosis. In asbestosis, asbestosis bodies appear. Finally, ferruginous bodies are typical for inhalation of inorganic dust with deposition of ferrous materials. ^{[14] [13] [15]}

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

Pneumoconiosis is caused by the inhalation of airborne dust and fibers that are either organic or inorganic. The specific cause depends on the specific pneumoconiosis. ^[1]

Common causes of pneumoconiosis may include: ^{[2] [3] [4]}

• Silicosis – silica
• Coalworker’s pneumoconiosis
• Asbestosis – asbestos fibers
• Berylliosis – beryllium dust

Less common causes of pneumoconiosis include: ^{[2] [3] [4] [5]}

• Talcosis – talc
• Siderosis – iron
• Hard metal pneumoconiosis
• Byssinosis – cotton

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

Pneumoconiosis must be differentiated from other diseases that cause chronic cough and dyspnea.

Pneumoconiosis must be differentiated from other diseases that cause cough and dyspnea.

On the basis of cough and chronic dyspnea, pneumoconiosis must be differentiated from lung malignancy, tuberculosis, emphysema, asthma, interstitial lung disease, pneumonia, and sarcoidosis. ^{[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]}

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

In 2010, a study indicated that pneumoconiosis accounted for 125,000 deaths worldwide, with 3495 attributed to asbestosis. Pneumoconiosis incidence has increased in workers that have been exposed to occupational dust. ^{[1] [2]}

• The incidence of pneumoconiosis increases with age. ^[3]

• Pneumoconiosis affects all races but African Americans have a higher rate of developing the condition when exposed to the same particles. ^[4]

• Males are more commonly affected by pneumoconiosis. ^[3]

• Pneumoconiosis is one of the most common occupational diseases, especially in developing countries.
• In developed countries, asbestosis is the predominant pneumoconiosis whereas in developing countries it is either silicosis or coal worker’s pneumoconiosis. ^[5]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

Risk factors for the development of pneumoconiosis depend on exposure, which is generally through certain occupations.

Risk factors in the development of pneumoconiosis are occupational. ^{[1] [2] [3] [4] [5] [6] [7]}

• Common risk factors in the development of pneumoconiosis include:
  • Stonemasons, quarry workers, tunnellers, foundry, pottery workers (Silicosis)
  • Construction workers
  • Length of employment positively correlates
  • Drilling
  • Mining
  • Sandblasting
  • Concomitant smoking
  • Textiles
  • Shipbuilding
  • Electronic shops
  • Automotive industry
  • Aerospace

• Less common risk factors in the development of pneumoconiosis include:
  • Environmental exposure in buildings
  • Community-acquired in neighborhoods

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

Screening for pneumoconiosis includes using chest radiography on workers exposed to certain particles as a part of preventative care. ^{[1] [2]}

Chest radiography is used as a screening tool for workers as a part of primary prevention. However, HRCT is more sensitive and specific. Future methods of screening workers include measuring serum SMRP and fibulin-3, CEA, and urinary 8-OHdG and breath testing of pentane, C5-C7 alkanes, and methylated alkanes. ^{[3] [4] [5]}

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dushka Riaz, MD

Prognosis is generally poor, and mortality rates vary depending on the specific pneumoconiosis. For example, berylliosis patients mortality rates are between 6 to 35%. ^{[1] [2]}

• The symptoms of pneumoconiosis typically develop 10-20 years after exposure to the specific particle, for example, silica in the case of silicosis. ^[2]

• Common complications of pneumoconiosis include: ^{[3] [4] [5] [6] [7] [8] [9] [10] [11] [12]}
  • Pulmonary fibrosis (accelerated by concomitant cigarette smoking)
  • Emphysema
  • COPD
  • Pleural effusion
  • Pleural plaques
  • Malignant Mesothelioma (Asbestosis)
  • Carcinoma
  • Tuberculosis
  • Scleroderma
  • SLE
  • Glomerulonephritis
  • Pulmonary hypertension
  • Cor pulmonale
  • Respiratory failure
  • Chronic necrotizing aspergillosis (Silicosis)
  • Rheumatoid arthritis
  • Chronic kidney disease
  • Sarcoidosis
  • Bronchitis

The prognosis for pneumoconiosis is poor and leads to respiratory complications and premature death. The prognosis is deemed to be poor particularly when fibrosis is found on CT scans. ^{[2] [13] [14]} Patients progress quickly to cor pulmonale and respiratory failure. In the case of silicosis, the survival is generally less than four years. ^{[15] [16]}

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