Asbestos-related lung disease

In this CCC we will cover asbestosis and mesothelioma.

ASBESTOSIS

Asbestosis is diffuse interstitial lung fibrosis due to the exposure of asbestos. Asbestos is a carcinogenic fibrous material that is an effective insulator. It was used in insulation, roofing, flooring, ceilings and walls but has been banned in the UK since 1999.

Asbestos are made of long, thin fibrous crystals. Each of these fibres is made up of microscopic fibrils which can be released into the air. It is a type of pneumoconiosis which is just the general term used to describe interstitial lung diseases that occur due to dust inhalation (we will discuss some other types of pneumoconiosis in the CCC on occupational lung diseases).

🏡 Epidemiology

In the UK there were 517 asbestosis-related deaths (excluding mesothelioma) in 2017 alone. It has been decreasing since its ban as there is a latency period of ~20 years from first exposure to development of radiographically identifiable changes. So nowadays those being diagnosed typically are >50 years old. Unfortunately, its use in developing countries is increasing.

It is especially common in those who worked in construction, shipyards, automobile industry, housing, and textiles industries.

Men account for the overwhelming majority of cases as they were more exposed to it in the industries in which its use was prevalent. Women tend to have been exposed at home (due to contamination of work clothes) or in the environment.

Pathophysiology

Upon inhalation of asbestos fibres, they are deposited at the bifurcation of alveolar ducts. This causes inflammation from alveolar macrophages which release cytokines such as TNF and IL-1 as well as ROS which initiates the process of fibrosis by fibroblasts. It typically happens in the lower lobes and can progress to honeycombing (destroyed and fibrotic lung tissue containing numerous cystic airspaces with thick fibrous walls).

⚠️ Risk factors

• Occupational exposure - the greater the exposure, the greater the risk of asbestosis. The cumulative dose needed to see pleural changes is less than the dose needed for asbestosis.
• Smoking - reduces the lung’s ability to clear the asbestos fibres.

😷 Presentation

🔍 Investigations

As it has a lengthy latency period, a history is important to elicit the possibility of exposure to asbestos and to understand the extent of exposure.

Imaging and pulmonary function tests may follow to confirm a diagnosis:

📷

Imaging:

1. CXR - PA and lateral will be needed. It is less sensitive than a CT scan, however. The presence of interstitial fibrosis predominantly in the lower zones along with pleural thickening is highly specific to asbestosis.
2. High-resolution CT chest (HRCT) - will also show lower zone interstitial fibrosis and pleural thickening.

Pulmonary function tests:

They may be normal, or they may show a restrictive pattern:

• This is seen as a reduced FVC and reduced total lung capacity (TLC) but normal FEV1/FVC ratio (as the lung is unable to expand as much to fill the space but it can still remove the air normally).
• It may also have an obstructive pattern or a mixed restrictive-obstructive pattern. It is not very specific unfortunately.

If cancer is suspected, we can do an open lung biopsy for a more definitive diagnosis.

👀 Screening

The Occupational Safety and Health Administration (OSHA) require that workers exposed to >0.1fibres/cm³ have an annual exam which includes a history, physical examination, respiratory examination and spirometry. A CXR is needed every 5 years within the first 10 years from the onset of exposure as well as for patients <35 years old.

🧰 Management

There are no interventions that offer a significant benefit unfortunately. Therefore the first-line options are:

• Smoking cessation
• Pulmonary rehabilitation - exercise training, education and psychosocial support.
• Oxygen therapy - if SpO2 <89%.

Patients with end-stage respiratory failure are potential candidates for lung transplants.

💵 Compensation

If the individual has developed asbestosis due to occupational exposure they may be eligible for claim compensation.

💬 Referral

It is also important to note that all patients with known exposure to asbestos need to be referred to the coroners.

MESOTHELIOMA

Mesothelioma is a cancer that affects the pleura (90%), peritoneum (5-10%), pericardium (<1%) and tunica vaginalis of the testes (<1%).

It is commonly associated with asbestos exposure with 80% of patients having a history of asbestos exposure. It is an aggressive cancer with a median survival time of 8-14 months.

The pathophysiology relates to the activation of macrophages and neutrophils which produce pro-inflammatory cytokines which cause a cumulative oxidative stress that damages DNA and alters gene expression (of oncogenes and tumour suppressor genes) which causes malignant transformations. The most frequent mutations relate are:

1. Neurofibromatosis 2 (NF2)
2. BRCA1-associated protein (BAP1)
3. Cullin 1 genes (CUL1)

⚠️ Risk factors

😷 Presentation

1. Progressive shortness of breath (usually due to large pleural effusion or trapped lung) is the most prevalent symptom.
2. Chest pain
3. Pleural effusion - due to leaking of blood, lymph and fluid into the pleural cavity. This can lead to diminished breath sounds and dullness to percussion.
4. Cough - dry and non-productive.
5. Weight loss - a red-flag symptom
6. Fatigue, fever, sweats

🔍 Investigations

🏆 Pleural biopsy is the gold-standard to confirm diagnosis. It can be obtained with thoracentesis (malignant cells may be seen in pleural fluid), transthoracic needle aspiration, tissue core specimen or video-assisted thoracoscopic surgery (VATS). VATS is considered the best as it can also be used to evaluate the pleural lining and obtain specimens.

🧰 Management

Prognosis is poor and most patients are offered palliative chemotherpay.