AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

Coal worker's pneumoconiosis (CWP) can be defined as the accumulation of coal dust in the lungs and the tissue's reaction to its presence.¹ The disease is divided into 2 categories: simple CWP (SCWP) and complicated CWP (CCWP), or pulmonary massive fibrosis (PMF), depending on the extent of the disease.

Pathophysiology

Anthracosis is the asymptomatic accumulation of coal pigment without consequent cellular reaction. Such accumulation can be found in varying degrees among most urban dwellers and in tobacco smokers. Inhaled coal dust becomes a problem when the body's natural defense and processing of the dust becomes overwhelmed and, subsequently, overreactive.

Inhaled coal dust enters the terminal bronchioles, and the carbon pigment is engulfed by alveolar and interstitial macrophages. Phagocytosed coal particles are transported by macrophages up the mucociliary elevator and are expelled in the mucus or through the lymphatic system.

When this system becomes overwhelmed, the dust-laden macrophages accumulate in the alveoli and may trigger an immune response. (The lungs must be exposed for a significant amount of time to dust particles 2-5 µm in diameter in order to be retained in the alveoli.) Fibroblasts involved in this response secrete reticulin, which entraps the macrophages. If the macrophages lyse, the fibroblastic response is augmented and more reticulin is laid down in the area.

Coal that contains silica lyses macrophages faster and stimulates the fibroblasts to add more collagen to the network. The lymphatic tree is contained in the pulmonary interstitium, along with arterial and venous vessels. If these macrophages have partially migrated up the lymphatic vessels, arterioles can become strangulated from the resultant interstitial fibrosis. As more and more dying macrophages, fibroblasts, reticulin, and collagen are deposited along the vascular tree, the vessels become compromised, and ischemic necrosis ensues.

Areas of focal deposition of coal dust and pigment-laden macrophages are known as coal macules and are the histologic hallmark of CWP. As these macules extend, they join other macules in the vicinity, forming discrete areas of interstitial fibrosis. This growing collagen network causes distention of the respiratory bronchioles, forming focal areas of emphysema. Widespread areas of focal emphysema can accrue without significant respiratory impairment.

Depending on factors that are still not fully understood, the macules may arrest or may continue to enlarge and form nodules that produce PMF when they coalesce. This process can be exacerbated by tuberculosis or rheumatoid factor, which accelerates the rate of progression of focal ischemic necrosis and fibrosis.

PMF in association with rheumatoid arthritis is known as Caplan syndrome. Caplan first described this condition in 1953. He noticed that miners with rheumatoid arthritis had changes on chest radiographs similar to those of PMF, although the distribution in the lungs was different. Unlike lesions caused by PMF, which congregate in the upper lobes, these new lesions (subsequently known as Caplan lesions) tend to coalesce in the peripheral lung fields.

Pathologically, the nodule exhibits a central area of necrotic collagen and coal dust lying in concentric rings. Surrounding these rings is an area of neutrophils with palisading fibroblasts. Caplan nodules tend to progress faster than lesions associated with PMF and may precede the onset of rheumatoid lesions. Sixty-two percent of miners with peripheral nodules have positive serology findings for rheumatoid factor.²

Research is currently underway to further understand the inciting factors in the inflammatory process. Boitelle et al³ have suggested that chemokines released to attract alveolar macrophages may be a plausible target for further pharmaceutical intervention to arrest the inflammatory process, which leads to destruction and fibrosis. Levels of monocyte chemoattractant protein-1 have been found to be increased in bronchoalveolar lavage specimens taken from patients with SCWP or PMF compared with controls. This chemokine, which attracts and activates monocytes, is responsible for the domino effect of respiratory burst, further cell recruitment, and release of lysosomal enzymes. This chemokine may be a key factor in the chronic inflammation of the macrophage, which is central to the pathophysiology of CWP.³

Other interesting areas that may become promising are the antioxidants selenium and glutathione peroxidase. Both substances have been found to be at lower concentrations in patients who have been exposed to coal-mine dust and tobacco smoke compared with control subjects. This suggests a consumptive process and a weakened defense against reactive oxygen species, which cause cellular damage and potentiate CWP and PMF.⁴

In a 2005 study by Huang et al,⁵ a correlation has been found between bioavailable iron (BAI), pyrite concentration, and the regional progression of lung disease. BAI is iron that dissolves in 10 mmol/L phosphate solution at pH 4.5, which mimics the interior of lysosomes. Huang et al⁵ found an increased prevalence of CWP and PMF at Pennsylvania mines, where BAI values are higher, compared with Utah mines, where BAI levels are lower. They also demonstrated that pyrite-containing coal contributed to the higher prevalence of progression to CWP and PMF in Pennsylvania.

When mixed with water, pyrite produces hydrogen peroxide^{6, 7} and hydroxyl radicals.^{8, 9} These reactive agents have been shown to degrade yeast RNA, ribosomal RNA, and DNA.⁷ Cohn et al¹⁰ demonstrated that these pyrite-induced reactive oxygen species can be implicated as the cause of the cellular damage and chronic inflammation that lead to chronic disease in the lungs of coal miners. In order to proceed to RNA degradation, the concentration of sulfur (pyrite) in the coal necessary to produce hydrogen peroxide and hydroxyl radicals must exceed 1%.¹⁰ These findings suggest that personnel at individual mines can measure the amount of sulfur in its coal and implement proper measures to ensure that miners in these high-risk areas either have improved protective gear or decreased long-term exposure to coals with increased BAI.

Frequency

United States

The prevalence of CWP is related to the length and the type of exposure to coal dust and is therefore more prevalent in people exposed to higher concentrations. In the United States, most coal is mined in eastern Pennsylvania, western Maryland, West Virginia, Virginia, and Kentucky. Disease prevalence varies in different areas of the country and from mine to mine because coal content varies by region. In the 1960s, the Interagency Study determined the overall prevalence of CWP to be 30% and the overall prevalence of PMF to be 2.5%.¹ Sixteen percent of coal miners in the United States can progress to interstitial fibrosis.¹¹

A 2004 study¹² reviewed death certificates from 1968-1982 and 1982-2000 with CWP as the cause of death.  A 36% decrease was noted in the reporting of male deaths due to CWP from 1982-2000 compared with from 1968-1982. This overall decline is likely multifactorial, due to the decline of the coal-mining workforce in general and the institution of the Federal Coal Mine Health Safety Act. Despite these national findings, regions of the country have demonstrated an increase in the progression to CWP and PMF in Kentucky and Virginia.¹³ This has prompted studies researching the caustic content of coal in isolated mines, which may be contributing to a regional variation in the progression of lung diseases.

International

In Great Britain, most coal is mined in Wales. As in the United States, 16% of miners can progress to interstitial fibrosis.¹¹

Mortality/Morbidity

Mortality and morbidity are strictly related to the type of coal dust and the length of exposure. Disease severity increases as coal rank increases and in miners who have greater exposure to respirable dust. As a result, CWP is rarely observed in coal miners younger than 50 years.²

A recent 41-month retrospective study performed by Shen et al¹⁴ describes a prognostic relationship between CWP and the first episode of respiratory failure requiring mechanical ventilation. The investigators found that radiographic evidence of PMF was not associated with increased ICU mortality. No mortality difference was delineated between patients with SCWP and patients with CCWP. The following 3 independent variables predicted outcomes:

• Hypercapnia (PaCO₂ >45 mm Hg) at the time of intubation exhibited a protective effect, suggesting a less severe acute illness as the cause of the respiratory failure compared with normocapnic individuals.
• An Acute Physiology and Chronic Health Evaluation II (APACHE II) score greater than 25 at the time of intubation was associated with a worse mortality rate.
• A ratio of PaO₂ to fraction of inspired oxygen (FiO₂) of less than 200 mm Hg at the time of intubation was associated with a worse mortality rate.

Race

CWP has no predilection for any racial or ethnic group.

Sex

CWP has no predilection for either sex.

Age

The onset of CWP does not occur at any specific age. The onset of disease depends on the length and severity of exposure to coal dust and thus depends on when the coal miner began working in the mines and the specific nature of his or her exposure.

CLINICAL

Section 3 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

History

Taking a good history is perhaps the most important step in evaluating for CWP. Ask patients what their specific job entails in order to determine exposure to respirable coal dust. The length of time spent underground and the age at first exposure are important in determining the risk of progressing to PMF. Determine the type of coal mined, its rank, and, if possible, its silica content. Obtain a smoking history because miners who smoke have more symptoms than miners who do not smoke.

Treatment for CWP is palliative and preventive. Most miners are not receptive to recommendations to change career. If their respiratory status worsens, or if they are at risk for progression to PMF, suggest changing to a job within the mine that requires less exposure to respirable dust.

Physical

Miners with SCWP are usually asymptomatic. They may report cough or sputum production, but this is generally secondary to industrial bronchitis or smoking and not to the body's reaction to coal.¹¹ CCWP produces cough, dyspnea, and lung function impairment. If the disease is advanced, cor pulmonale may be found with associated right ventricular heave, large A waves, hepatomegaly, and peripheral edema. These late physical findings are rare in the United States.¹¹

CWP results from mechanical and architectural destruction of the lungs. Fever, night sweats, and other constitutional symptoms suggest a secondary infective process.

Causes

The following factors increase the risk of CWP:

• Type of dust: More silica increases the risk of fibrosis. Coal rankings are as follows²:
• • High: This coal is older and has the least amount of volatile matter (eg, anthracite coal [hard and shiny]).
  • Medium: This coal is of moderate age and has a greater amount of volatile matter (eg, bituminous coal).
  • Low: This coal is younger and has the greatest amount of volatile matter (eg, lignite coal [brown and crumbly]).
• Age at first exposure
• Length of time spent underground
• Smoking
• Size of dust particles
• Type of job: Certain jobs require more exposure to respirable dust. Most dust is found at the coal face; therefore, individuals who work directly on the cutting of the coal have the highest exposure. The following list details dust exposure related to job title, beginning with the highest exposure¹:
• • Cutting-machine operator: This worker cuts coal directly at the face. Respirable dust levels are highest here.
  • Roof bolters: These individuals drill through rock and thus are also exposed to silica. The continuous mine operator, loading machine operator, and shot firer are also exposed to higher amounts of respirable dust.
  • Train operators: They drop sand onto the tracks for traction and may therefore develop silicosis.
  • Motormen, brakemen, drivers, and shuttle car operators: These individuals have less dust exposure because the coal has already been cut by the time they work with it, thus decreasing their exposure to respirable dust.
  • Mechanics, electricians, and maintenance personnel: They have the least amount of dust exposure.

DIFFERENTIALS

Section 4 of 11  

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WORKUP

Section 5 of 11  

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Lab Studies

Obtain a CBC count and perform a sputum culture (as needed) to exclude infective processes.

Imaging Studies

Historically, radiographs remain the main diagnostic tool. The International Labor Organization developed a 12-point classification for standardizing the diagnosis of CWP. A standard set of radiographs reflecting the amount of coal retained in the lungs is used for comparison. The scale represents a continuum of dust accumulation with nodule formation from category 0/0 to 3/4. Generally, CCWP appears on a background of category 3 or 4 SCWP.

SCWP usually develops as small, rounded opacities first observed mostly in the upper lobes. These densities can be classified as follows: 

• P - Up to 1.5 mm in diameter
• Q - 1.5-3 mm in diameter
• R - 3-10 mm in diameter

The lung zones are identified as follows:  

• RUZ and LUZ - Right upper zone and left upper zone, respectively
• RMZ and LMZ - Right mid zone and left mid zone, respectively
• RLZ and LLZ - Right lower zone and left lower zone, respectively

Any nodular opacity greater than 1 cm in diameter on radiographs is considered CCWP or PMF. Subcategories for this group are as follows:  

• A - Any opacity 1-5 cm in diameter
• B - Any opacity with a diameter of 5 cm that occupies less than a third of the lung
• C - One or more opacities whose diameter exceeds a third of the total area of the lung

Other Tests

On pulmonary function test results, persons with SCWP do not show significant impairment of lung function or a decrease ventilatory capacity. A slight decrease in the alveolar-arterial pressure gradient can be observed, along with a minor reduction in diffusing capacity (P category) and minimal hypoxemia observed in categories 2 and 3 (secondary to physiological shunting). If present, focal emphysema can result in a slight increase in compliance of the lung and an increase in residual volume.¹¹

With regard to pulmonary function tests in persons with CCWP, abnormalities are detected in stages B and C. Ventilatory capacity is reduced in proportion to the size of the conglomerate mass.¹¹ Diffusing capacity is also decreased. If the mass is large enough to destroy significant vascularity, pulmonary hypertension ensues. Additionally, hypoxemia develops earlier and more frequently in miners who smoke.

In their 4-year longitudinal study, Bourgkard et al¹⁵ determined that "worsening x-ray findings and pneumoconiosis were more often observed in coal miners with micronodules on CT scans, wheezing, low values of maximal midexpiratory flow (MMEF) and forced expiratory flow (FEF_25-75%), and high dust exposure at first examination." This finding suggests that the presence of micronodules on CT scans, altered scores on pulmonary function tests, and wheezing signify a worse 4-year prognosis and increased risk of progression to PMF. CT scanning, therefore, might be a helpful screening tool to monitor progression to pneumoconiosis.

Vallyathan et al¹⁶ found that "in miners without CWP antioxidants, cytokine and growth factors are maintained at baseline levels present in control subjects." In contrast, miners with SCWP exhibit markedly elevated bronchoalveolar lavage fluid concentrations of antioxidants, proinflammatory cytokines, and mediators, which increase fibroblast proliferation. The inability of the lungs to maintain a balance between oxidant burden and antioxidant defenses may play a crucial role in the genesis of the disease. Increased levels of interleukins 1 and 6, tumor necrosis factor-alpha, transforming growth factor-beta1, transforming growth factor-beta2, alpha1-proteinase inhibitor, and fibronectin were found in the bronchoalveolar lavage fluid of miners with radiographically defined CWP.

TREATMENT

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Medical Care

• Treatment for both SCWP and CCWP is symptomatic. Use oxygen as hypoxemia demands.
• No evidence supports the hypothesis that removing the miner from the mining environment arrests the disease once progression to PMF has begun. Therefore, serially monitoring the chest radiographs of miners in order to prevent the development of CCWP is prudent. Advise workers who develop evidence of SCWP to transfer to jobs with low dust exposure.
• Smoking has an additive effect on CWP; therefore, strongly recommend smoking cessation.
• Caplan syndrome is treated similarly to PMF. Oxygen and bronchodilators are administered as needed. The rheumatoid component is treated separately, per rheumatological protocol.
• All patients should receive immunizations for influenzae and pneumococci.
• Seriously consider the possibility of superimposed mycobacterial infection in any patient with unexplained weight loss, chronic cough, fever, or night sweats.

Consultations

Consultation with a pulmonary medicine specialist is required.

MEDICATION

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The goals of pharmacotherapy are to reduce morbidity and to prevent complications.

Drug Category: Respiratory agents

Are used to treat hypoxemia.

FOLLOW-UP

Section 8 of 11  

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Further Inpatient Care

Once a baseline radiograph has been established, patients should have follow-up radiographs every 5 years—more often if symptoms worsen.

Deterrence/Prevention

CWP is a completely preventable disease. As such, the Coal Mine Health and Safety Act of 1969 limited miner's exposure to respirable dust to less than 1 mg/m³. Miners are encouraged to have an initial chest radiograph on the date of hire and at 5-year intervals thereafter.

Complications

Closely monitor patients who have developed diffuse interstitial fibrosis for progression to peripheral squamous cell carcinoma (SCC) because diffuse interstitial fibrosis is a potent accelerator of this type of cancer. Katabami et al¹⁷ determined that a "positive causal relationship between pneumoconiosis and peripheral-type SCCs of the lung" exists.

Prognosis

Prognosis is poor once the patient has been determined to have PMF. Treatment is palliative.

MISCELLANEOUS

Section 9 of 11  

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• Miscellaneous
• Multimedia
• References

Medical/Legal Pitfalls

CWP is an occupation-related illness, and compensation issues are often a relevant concern for patients. A physician may be asked to estimate the proportion of respiratory impairment present referable to coal dust exposure. Given the importance of specific knowledge of relevant statutes in order to ensure appropriate compensation, consultation with an occupational health specialist or pulmonary physician may be appropriate.

MULTIMEDIA

Section 10 of 11  

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• Workup
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• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Gross specimen demonstrating simple coal worker's pneumoconiosis.
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Media file 2:  Gross specimen demonstrating progressive massive fibrosis in a coal miner.
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REFERENCES

Section 11 of 11

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1. Morgan WK, Seaton A. Occupational Lung Diseases. Philadelphia, Pa: WB Saunders; 1975:149-210.
2. Haselton PS. Spencer's Pathology of the Lung. 5^th ed. New York, NY: McGraw-Hill; 1996:475-83.
3. Boitelle A, Gosset P, Copin MC, Vanhee D, Marquette CH, Wallaert B, et al. MCP-1 secretion in lung from nonsmoking patients with coal worker's pneumoconiosis. Eur Respir J. Mar 1997;10(3):557-62. [Medline].
4. Nadif R, Oryszczyn MP, Fradier-Dusch M, Hellier G, Bertrand JP, Pham QT, et al. Cross sectional and longitudinal study on selenium, glutathione peroxidase, smoking, and occupational exposure in coal miners. Occup Environ Med. Apr 2001;58(4):239-45. [Medline].
5. Huang X, Li W, Attfield MD, Nadas A, Frenkel K, Finkelman RB. Mapping and prediction of coal workers' pneumoconiosis with bioavailable iron content in the bituminous coals. Environ Health Perspect. Aug 2005;113(8):964-8. [Medline].
6. Borda MJ, Elsetinow AR, Schoonen MA, Strongin DR. Pyrite-induced hydrogen peroxide formation as a driving force in the evolution of photosynthetic organisms on an early earth. Astrobiology. 2001;1(3):283-8. [Medline].
7. Cohn CA, Pak A, Schoonen MA, Strongin DR. Quantifying hydrogen peroxide in iron-containing solutions using leuco crystal violet. Geochem Trans. 2005;6(3):47-52.
8. Cohn CA, Borda MJ, Schoonen MA. RNA decomposition by pyrite-induced radicals and possible role of lipids during the emergence of life. Earth Planet Sci Letters. 2004;225(3-4):271-8.
9. Cohn CA, Mueller S, Wimmer E, Leifer N, Greenbaum S, Strongin DR, et al. Pyrite-induced hydroxyl radical formation and its effect on nucleic acids. Geochem Trans. 2006;7:3. [Medline].
10. Cohn CA, Laffers R, Simon SR, O'Riordan T, Schoonen MA. Role of pyrite in formation of hydroxyl radicals in coal: possible implications for human health. Part Fibre Toxicol. 2006;3:16. [Medline].
11. Baum GL, Crapo JD, Celli BR. Textbook of Pulmonary Diseases. Vol 1. Philadelphia, Pa: Lippincott-Raven; 1998:683-92.
12. Centers for Disease Control and Prevention. Changing patterns of pneumoconiosis mortality--United States, 1968-2000. MMWR Morb Mortal Wkly Rep. Jul 23 2004;53(28):627-32. [Medline].
13. MD Attfield, PhD, EL Potsonk, MD. Advanced pneumoconiosis among working underground coal miners--Eastern Kentucky and Southwestern Virginia, 2006. MMWR Morb Mortal Wkly Rep. Jul 6 2007;56(26):652-5. [Medline].
14. Shen HN, Jerng JS, Yu CJ, Yang PC. Outcome of coal worker's pneumoconiosis with acute respiratory failure. Chest. Mar 2004;125(3):1052-8. [Medline].
15. Bourgkard E, Bernadac P, Chau N, Bertrand JP, Teculescu D, Pham QT. Can the evolution to pneumoconiosis be suspected in coal miners? A longitudinal study. Am J Respir Crit Care Med. Aug 1998;158(2):504-9. [Medline].
16. Vallyathan V, Goins M, Lapp LN, Pack D, Leonard S, Shi X. Changes in bronchoalveolar lavage indices associated with radiographic classification in coal miners. Am J Respir Crit Care Med. Sep 2000;162(3 Pt 1):958-65. [Medline].
17. Katabami M, Dosaka-Akita H, Honma K, Saitoh Y, Kimura K, Uchida Y, et al. Pneumoconiosis-related lung cancers: preferential occurrence from diffuse interstitial fibrosis-type pneumoconiosis. Am J Respir Crit Care Med. Jul 2000;162(1):295-300. [Medline].
18. Antao VC, Petsonk EL, Sokolow LZ, Wolfe AL, Pinheiro GA, Hale JM, et al. Rapidly progressive coal workers' pneumoconiosis in the United States: geographic clustering and other factors. Occup Environ Med. Oct 2005;62(10):670-4. [Medline].
19. Centers for Disease Control and Prevention. Pneumoconiosis prevalence among working coal miners examined in federal chest radiograph surveillance programs--United States, 1996-2002. MMWR Morb Mortal Wkly Rep. Apr 18 2003;52(15):336-40. [Medline].

Article Last Updated: Sep 5, 2007