Anthracosis (Miner's Asthma)

Miner spirometry (9253624711)[1]

Anthracosis is a form of pneumoconiosis, a chronic pulmonary disease resulting from prolonged inhalation of dust. This condition results from prolonged inhalation of soot or coal dust particles which render the lungs black.

The disorder is triggered by the following process: Poison.

Presentation

Because anthracosis results from prolonged exposure to coal dust or soot particles, diagnosis of this condition is largely based on anamnesis. Patients may report to have worked in coal mines, but any other occupation or living conditions associated with these risk factors may also hint at anthracosis. In one study, traditional indoor baking has been related with anthracosis [3]. The age at first exposure and its overall time should be taken into account. It is important to know if the patient smokes, since smoking may trigger or aggravate symptoms like chronic productive cough, dyspnea and reduced tolerance to exercise. In patients suffering from advanced anthracosis or anthracofibrosis, symptoms of right heart failure may develop [6]. These individuals may additionally suffer from fatigue, severe dyspnea even at rest, cyanosis, venous congestion and peripheral edema. Such severe cases of anthracosis are rare and the majority of patients is indeed asymptomatic.

Workup

If the medical history of a patients indicates a chronic exposure to coal dust or soot particles, anthracosis should be considered before confirming diagnosis of chronic obstructive pulmonary disease, asthma, tuberculosis or idiopathic pulmonary fibrosis [7]. The gold standard for the diagnosis of anthracosis is bronchoscopy, a technique that allows visualization of black depositions on respiratory mucous membranes and smooth narrowing of the bronchial tubes. Computed tomography scans often reveal enlargement and calcification of regional lymph nodes. Further characteristic findings include diffuse calcification, atelectasis, emphysema and pleural effusion [8] [9]. Mass lesions may require biopsy and histopathological analysis.

Pulmonary function tests, particularly spirometry, should be carried out to assess the extent of lung damage.

Of note, anthracosis possibly facilitates mycobacterial infections and large numbers of anthracosis patients also suffer from tuberculosis [5] [10]. Here, interferon-γ release assays, bacterial cultures and molecular biological confirmation of Mycobacteria spp. are the diagnostic measures of choice. Sputum samples obtained during bronchoscopy may be used for the latter.

Treatment

Causative treatment for anthracosis is not available. Thus, therapy is palliative and aims at preventing exacerbation.

In most cases, the source of coal dust or soot particles may easily be identified. If it persists, exposure should be reduced as far as possible. Unfortunately, job changes are often not an option. However, shifting the affected worker to an area with less exposure to volatile matter may be possible.

Patients should be strongly advised not to smoke.

Rehabilitation programs may improve dyspnea, tolerance to exercise, and overall quality of life. Exercise is an important part of such programs but should start slowly.

Severe cases of anthracosis or anthracofibrosis, i.e., those presenting a very low arterial oxygen saturation, may require continuous oxygen therapy. Nocturnal oxygen desaturation may occur and blood gas analyses conducted at daytime may thus underestimate the risk for hypoxia. If desaturation at night is a problem, oxygen therapy should be applied while the patient is sleeping.

Patients may additionally benefit from bronchodilators.

If response to therapy is not satisfactory, patients should be considered for lung transplantation.

In some countries, occupational rights may entitle affected workers to compensation [11]. Thus, they should be advised to invoke these rights, possibly after seeking legal counseling.

Prognosis

Prognosis depends on the severity of disease. Although the condition is not reversible, mild cases do not necessarily affect the quality of life. Anthracofibrosis has a poor diagnosis.

Etiology

Anthracosis is a typical occupational disease of coal miners, although it has been reported in patients that have never been working below ground [3].

In general, a young age at first exposure, prolonged exposure, i.e., several years of working underground or in any other environment loaded with high amounts of soot particles, and smoking are the main risk factors for this disease. There is a clear correlation between the aforementioned parameters and the severity of anthracosis.

Additionally, the size of coal dust or soot particles affects the development of anthracosis. Both are generally estimated to measure between 1 and 100 µm, i.e., although many particles are retained at bronchial tube level, the smaller share of such particles may penetrate into the bronchioles and possibly even into the alveoli.

Coal miners may work with distinct types of carbonaceous rocks that may contain more volatile material than others. In general, the older the coal, the more compact it is. Anthracite, for instance, comprises small amounts of volatile matter and thus exposure to it bears much lower risks of anthracosis than the same amount of exposure to lignite. Also, certain types of jobs within coal mines may involve greater exposure to volatile matter than others.

Epidemiology

Definitive diagnosis of anthracosis requires bronchoscopy. Since many patients suffering from mild to moderate anthracosis remain asymptomatic, black depositions on the respiratory mucous membranes are often incidental findings. Furthermore, there is no clear definition for the terms healthy respiratory tract and anthracosis. In smokers, this may be a very challenging question. Therefore, the overall prevalence of anthracosis may only be roughly estimated. In a large study comprising more than 14,000 bronchoscopies conducted in Iran, about 5% of all patients were found to show signs of anthracosis [4]. About one third of those patients suffered from anthracofibrosis. Of note, considerable differences in anthracosis prevalence between distinct geographical regions may exist. The true number of patients affected by anthracosis presumably depends on the occupation and life-style of the population, as well as on industry and air pollution of the respective country.

Due to the etiology of the disease, anthracosis is very rarely diagnosed in children. The mean age of symptom onset is 63 years [5]. Although there are more men among coal miners than women, anthracosis also affect females. In fact, many studies show even higher prevalence rates in women than in men [1].

Sex distribution
Age distribution

Pathophysiology

Inhalation of coal dust or soot particles initially leads to asymptomatic deposition on the mucous membranes of the respiratory tract. To a certain degree, this phenomenon can be observed in any smoker and in individuals living in urban environments.

If foreign bodies entering the respiratory tract cannot be removed by means of ciliary movement, macrophages will try to remove them. When only small quantities of particles are present, this process leads to subsequent excretion of particles in the mucus or removal by means of the lymphatic system. However, macrophages accumulate on the mucous membranes if coal dust or soot particles cannot be removed efficiently due to excessive amounts that exceed the self-cleaning capacities of the respiratory tract. These macrophages release pro- and anti-inflammatory mediators and trigger fibroblast proliferation. Matrix metalloproteinases, tissue inhibitors of metalloproteinases, and distinct cytokines may be released in this process. Unfortunately, growth of fibrous tissue further complicates removal of foreign bodies. In most cases though, inhalation of coal dust or soot particles continues for extensive periods and more dust accumulates in the respiratory tract.

Fibrosis does not only restrict the airways but may also contribute to the compression of vasculature and lymphatic vessels. This may lead to atelectasis and emphysema, and may also cause ischemic necrosis. All these processes worsen pulmonary gas exchange and arterial oxygen saturation and may ultimately provoke respiratory failure.

Anthracosis patients are particularly susceptible to infections with Mycobacterium spp. Tuberculosis is a comorbidity that aggravates the aforementioned pathophysiological processes.

Prevention

Implementation and application of measures for occupational safety largely contribute to prevention of anthracosis. This is not restricted to coal mining but also applies to any other profession that involves significant exposure to dust. Individuals performing such jobs should undergo regular examinations and thoracic radiographies.

Similarly, measures to reduce air pollution in general may be helpful to avoid anthracosis.

Smoking is not recommended by any means.

Summary

Anthracosis is a type of pneumoconiosis, a term referring to any chronic pulmonary disease caused by inhalation of considerable amounts of dust. While pneumoconiosis may be develop in individuals who chronically inhale asbestos, silica, or cotton, patients suffering from anthracosis have been exposed to coal dust or soot particles for prolonged periods of time. Thus, anthracosis is commonly seen in coal miners, and the condition is often referred to as coal worker's pneumoconiosis or black lung disease. Since anthracosis is an occupational disease, its diagnosis may have legal consequences wherein patients may be possibly entitled to financial compensation.

Deposition of coal dust on the mucous membranes of the respiratory tract may be an incidental finding. Majority of anthracosis patients are asymptomatic, whereas some develop chronic cough, dyspnea and intolerance to exercise [1]. Symptoms typically manifest in those individuals that have either been exposed to coal dust or soot for very long periods of time or those that have inhaled large amounts of dust in shorter time ranges. Smoking exacerbates anthracosis.

If ciliary movement is unable to remove coal dust or soot particles from the airways by ciliary movement, macrophages will attempt to remove these particles. Activation of macrophages results in the release of pro-inflammatory cytokines and induction of fibroblast proliferation. Due to this effect, severe cases of anthracosis are often associated with progressive massive fibrosis [2]. Because the particles mainly deposit in the bronchial tubes, this condition is also known as bronchial anthracofibrosis.

Pulmonary function tests can help assess the extent of the disease. Diagnostic imaging, particularly computed tomography scans, allows for an evaluation of pulmonary tissue and lymph nodes. Fibrosis and calcification are also common findings.

Therapy is palliative and is aimed at symptom relief and prevention of further exacerbation. The most important therapeutic measures are avoidance of coal dust or soot particle exposure and smoking cessation.

Patient Information

Anthracosis refers to a chronic pulmonary disease characterized by deposition of coal dust or soot particles on the mucous membranes of the respiratory tract.

Causes

Usually, any inhaled small particle is transported back upwards by means of the ciliary movement of the mucous membranes. Prolonged exposure to coal dust or soot particles, however, exceeds the self-cleaning capacities of the lungs and results in the aforementioned condition.

Coal miners inhale large amounts of coal dust that may be deposited on the mucous membranes. Similarly, anyone continuously exposed to smoke may develop this disease. Immune cells try to remove the inhaled particles and induce chronic inflammation and pulmonary fibrosis.

Smoking and air pollution exacerbate the disease.

Symptoms

Most patients remain asymptomatic for years. Symptoms such as productive cough, breathing difficulties and intolerance to exercise typically manifest in patients aged 60 years and older. Severe cases of anthracosis may lead to right heart failure.

Diagnosis

The patient's medical history is of the utmost importance in the diagnosis of anthracosis and the choice of treatment. This condition is confirmed by performing bronchoscopy and visualizing black depositions on mucous membranes of the respiratory tract. Pulmonary function tests and computed tomography scans are helpful to assess the extent of lung damage. The latter also serves to rule out differential diagnoses.

Treatment

There is no causative treatment for anthracosis. If at all possible, the patient should avoid the source of coal dust or soot particles. Any reduction of exposure to this matter also prevents exacerbation of the disease. If a job change is not an option, it may be possible to change to a position that involves less exposure to dust.

Smokers should stop smoking.

Exercise programs may help to relieve breathing difficulties and intolerance to exercise. They should be realized under professional supervision.

If the pulmonary gas exchange is strongly restricted, continuous oxygen therapy may be required. In some patients, blood oxygen saturation only drops at night and thus, oxygen supplementation is only necessary while sleeping.

Additional medication may provide some relief by widening the bronchial tubes. However, if this is not the case and the patient is at acute risk of respiratory failure, they may be considered for lung transplantation.

Of note, in some countries, occupational rights may entitle anthracosis patients to compensation.

Self-assessment

References

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  2. Laney AS, Petsonk EL, Hale JM, Wolfe AL, Attfield MD. Potential determinants of coal workers' pneumoconiosis, advanced pneumoconiosis open link open link, and progressive massive fibrosis among underground coal miners in the United States, 2005-2009. Am J Public Health. 2012; 102 Suppl 2:S279-283.
  3. Qorbani M, Yunesian M, Baradaran HR. Indoor smoke exposure and risk of anthracosis. Iran J Med Sci. 2014; 39(6):571-576.
  4. Sigari N, Mohammadi S. Anthracosis and anthracofibrosis. Saudi Med J. 2009; 30(8):1063-1066.
  5. Mirsadraee M, Saffari A, Sarafraz Yazdi M, Meshkat M. Frequency of tuberculosis in anthracosis of the lung: a systematic review. Arch Iran Med. 2013; 16(11):661-664.
  6. Agrawal A, Verma I, Shah V, Agarwal A, Sikachi RR. Cardiac manifestations of idiopathic pulmonary fibrosis. Intractable Rare Dis Res. 2016; 5(2):70-75.
  7. Laney AS, Weissman DN. Respiratory diseases caused by coal mine dust. J Occup Environ Med. 2014; 56 Suppl 10:S18-22.
  8. Kuempel ED, Wheeler MW, Smith RJ, Vallyathan V, Green FH. Contributions of dust exposure and cigarette smoking to emphysema severity in coal miners in the United States. Am J Respir Crit Care Med. 2009; 180(3):257-264.
  9. Ghanei M, Aslani J, Peyman M, Asl MA, Pirnazar O. Bronchial anthracosis: a potent clue for diagnosis of pulmonary tuberculosis. Oman Med J. 2011; 26(1):19-22.
  10. Mirsadraee MH, Asnashari AK, Attaran DM. Tuberculosis in patients with anthracosis of lung underlying mechanism or superimposed disease. Iran Red Crescent Med J. 2011; 13(9):670-673.
  11. Office of Workers' Compensation Programs, Labor. Black Lung Benefits Act: standards for chest radiographs. Final rule. Fed Regist. 2014; 79(74):21606-21615.

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Media References

  1. Miner spirometry (9253624711), Public Domain
Self-assessment