16th January 2024

Pneumoconiosis

Background

Pneumoconiosis is a group of chronic interstitial lung diseases that develop following inhalation of mineral or metal dust, predominantly found in the work environment. These include asbestosis, silicosis, coal worker’s pneumoconiosis and berylliosis. The aetiology of pneumoconiosis is detailed below. The main clinical sequelae of pneumoconiosis include progressive pulmonary fibrosis, inflammation and progressive respiratory or heart failure.

Table 1- Aetiology of pneumoconiosis (Adapted from Table 1, Brown, L. (2013) “ClinicalKey,” Journal of the Medical Library Association: JMLA, 101(4), pp. 342–343. doi: 10.3163/1536-5050.101.4.023. )

Silicosis

Silicosis is caused by inhalation of crystalline silica (silicon dioxide), the most abundant mineral on earth. The main clinical subtypes of silicosis are acute, accelerated, and chronic silicosis. 

Pathophysiology

Following inhalation, silica particles deposit in the airways. This produces macrophage activation, which exerts toxic effects on the lung parenchyma, provoking an inflammatory cytokine response. This process promotes fibrosis of the lung and formation of upper lobe silicotic nodules. 

Silicosis can be further categorised based on radiological findings- simple silicosis and progressive massive fibrosis (PMF). Simple silicosis is characterised by rounded nodules, less than 10mm in size, found predominantly in upper lung zones. In PMF, these nodules coalesce, causing upper lobe lung parenchyma, which causes fibrotic retraction of upper lobes, which contributes to air trapping and emphysema in the lower lobes. 

Presentation

Broad symptoms of chronic and accelerated silicosis include cough and dyspnoea, and examination may reveal a range of findings, including wheeze and crackles. In cases of PMF, respiratory impairment and symptoms are more severe. PMF is not associated with clubbing. 

Unfortunately, once silicosis occurs, the damage is irreversible, and despite removal of the causative agent, it may continue to progress. Inhalation of silica is linked to other diseases such as lung cancer, tuberculosis, connective tissue diseases and renal diseases.

Chronic silicosis features

• Patients are initially asymptomatic until an interval of 10-20 post-exposure.
• Normally associated with simple radiological pattern

Acute silicosis features (silicoproteinosis)

• This occurs following short duration of high-concentration exposure
• Presentation within one year of exposure
• Symptoms include non-productive cough, dyspnoea, weight loss, fatigue, fever, and pleuritic pain.

Accelerated silicosis features

• Onset of symptoms following 5-10 years of exposure
• Accelerated progression of disease
• At higher risk of PMF

Diagnosis

Imaging – CXR/ HRCT

• Simple silicosis features

• Well-defined upper zone opacities less than 10mm in size

• Progressive Massive Fibrosis features

• Larger, coalescent nodules
• Upper lobe fibrosis
• Hyperinflation of lower lobes 
• Hilar lymphadenopathy with eggshell calcification

Bronchoalveolar lavage 

• This is used to exclude other differentials
• Opaque effluent consistency
• Foamy macrophages and periodic acid-Schiff (pAS) staining

Berylliosis

Background

Berylliosis (also known as chronic beryllium disease) is a granulomatous lung disease caused by exposure to the alkaline earth metal beryllium. 

Pathophysiology

Beryllium exposure precipitates a delayed hypersensitivity cell-mediated immune response (Type IV hypersensitivity), which involves sensitisation to beryllium. Future exposure triggers proliferation of macrophages and CD4+ T lymphocytes, which aggregate in the lung. Over time, as this response progresses, these cells form noncaseating granulomas, which progress to fibrosis of the lung.

Presentation

• Predominantly a chronic disease, however, acute alveolitis secondary to beryllium exposure has been reported.
• Latency period between exposure and symptom onset varies from three months to thirty years.
• Common symptoms include dry cough, dyspnoea and, less often, constitutional symptoms such as weight loss, fatigue, and night sweats. 
• Physical examination findings include bi-basal crackles, rashes, cutaneous nodules, hepatosplenomegaly and clubbing in advanced disease.

Diagnosis

A definitive diagnosis of berylliosis requires all the following:

1. History of beryllium exposure
2. Beryllium lymphocyte proliferation test (BeLPT)
   • A positive blood or BAL test confirms sensitisation to beryllium
3. Tissue biopsy from bronchoscopy
   • This reveals non-caseating granulomas

Management

Corticosteroids are used in both acute and chronic berylliosis. In Chronic berylliosis, long-term glucocorticoid therapy is utilised with regular assessment (PFTs and imaging) to gauge response to treatment and plan future therapy. Immunosuppressants such as methotrexate and azathioprine are utilised in those who fail to respond to steroid therapy.

Coal worker’s pneumoconiosis (CWP)

Coal worker’s pneumoconiosis arises from chronic coal dust inhalation. Like silicosis, CWP may present as simple pneumoconiosis or may progress to progressive massive fibrosis (PMF). Incidence of disease is linked to total dust exposure.

Pathophysiology

Following inhalation, coal particles are retained in the alveoli. Macrophages then engulf these particles, triggering an immune response that precipitates fibrotic lung changes. CWP is also a known cause of chronic obstructive pulmonary disease (COPD).

Presentation

Simple CWP features:

• Asymptomatic
• Incidental small, rounded opacities found in the upper zones
• Associated with focal emphysema

Progressive massive fibrosis features:

• Coalescence of small nodules to form larger, widespread masses of fibrotic tissue
• Lesions may cavitate
• Symptoms include progressive dyspnoea, cough, and black productive sputum.

Caplan syndrome features:

• This syndrome describes a combination of pneumoconiosis and features of/diagnosis of Rheumatoid Arthritis 

Diagnosis 

Imaging 

Chest x-ray findings are similar to those found in Silicosis- small, rounded opacities in upper zones.

Pulmonary function tests

Mixed obstructive (due to emphysematous changes) and restrictive changes (due to fibrotic changes) 

Asbestosis

Asbestosis is a fibrotic lung disease caused by asbestos inhalation. Other asbestos-related pleural abnormalities may also present concurrently.

Pathophysiology

The deposition of inhaled asbestos fibres leads to alveolar macrophage alveolitis. This triggers an inflammatory response by releasing cytokines, including tumour necrosis factor (TNF) and interleukin-1 beta. This initiates the fibrotic process, which predominantly occurs in the lower lobes. 

Presentation

• History of progressive dyspnoea
• Cough, wheezing, and sputum production are less common
• Examination findings include bibasal end-inspiratory crackles, and clubbing may also occur
• Interval period between symptoms and exposure is normally over 20 years
• Severity of fibrotic disease is dependent on cumulative dose of exposure

Diagnosis

Imaging- Chest X-Ray/ HRCT

• Reticulonodular changes primarily in the lower lobes
• Concomitant pleural thickening and pleural plaques
• In advanced disease, reticulonodular changes become diffuse

Pulmonary function testing

• Restrictive pattern due to fibrotic changes
• Reduced transfer factor
• An obstructive pattern is uncommon in asbestosis- this is normally secondary to concomitant cigarette smoking history.

Overall management of Pneumoconiosis

There is no curative treatment for the chronic forms of pneumoconiosis (excluding berylliosis), and once fibrosis ensues, prognosis is poor. Therefore, the mainstay of management is supportive and focuses on symptom control and slowing or halting disease progression. 

• Early identification and removal of occupational exposure
• Smoking cessation
  • There is an increased risk of malignancy with both inhalation of mineral dust and smoking.
  • Cigarette smoking may also accelerate progression of pneumoconiosis 
• Bronchodilator therapy
  • COPD can be a complication of pneumoconiosis; therefore, in the presence of obstructive airways disease, bronchodilator therapy should be utilised
• Pulmonary rehabilitation
  • This a structured programme that incorporates exercise, patient health education, and behavioural change activities to improve symptom control, exercise tolerance and overall quality of life for chronic lung disease patients
• Long-term oxygen therapy (LTOT)
  • In end-stage ILD secondary to pneumoconiosis, LTOT may improve life expectancy.
  • Slows down progression of pulmonary hypertension secondary to hypoxaemia 

References

• Brown, L. (2013) “ClinicalKey,” Journal of the Medical Library Association: JMLA, 101(4), pp. 342–343. doi: 10.3163/1536-5050.101.4.023.
• Silicosis (no date) Bcmj.org. Available at: https://bcmj.org/worksafebc/silicosis (Accessed: April 12, 2022).
• bestpractice.bmj.com. (n.d.). Pneumoconioses – Symptoms, diagnosis and treatment | BMJ Best Practice. [online] Available at: https://bestpractice.bmj.com/topics/en-gb/1112?q=Pneumoconioses&c=suggested [Accessed 12 Apr. 2022].
• Sizar, O. and Talati, R. (2022). Berylliosis. [online] PubMed. Available at: https://www.ncbi.nlm.nih.gov/books/NBK470364/ [Accessed 12 Apr. 2022].
• www.uptodate.com. (n.d.). UpToDate. [online] Available at: https://www.uptodate.com/contents/asbestos-related-pleuropulmonary-disease.
• Qi, X.-M. et al. (2021) “Pneumoconiosis: current status and future prospects: Current status and future prospects,” Chinese Medical Journal, 134(8), pp. 898–907. doi: 10.1097/cm9.0000000000001461.
• DeLight N, Sachs H. Pneumoconiosis. [Updated 2021 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK555902/