Flashcards in Respiratory - Occupational lung disease Deck (31):
What are environmental and occupational lung diseases?
These are a wide range of pulmonary pathological reactions due to workplace exposure to fumes, gases, irritants, dusts and infections.
What is pneumoconiosis?
The non neoplastic response of lung to inhaled mineral or organic dusts but excluding asthma, or COPD. E.g. asbestosis, silicosis, coal miners pneumoconiosis
Why is particle size an important factor in disease production?
Small particles of 1-5microns can reach the distal airways and are deposited in the alveolar walls. This is because the movement of gas into and out of the lungs changes at the transition between the conducting and respiratory zones. Gas moves by diffusion from the respiratory bronchioles so small particles that are still too big to be carried by diffusion (but can reach this zone by convection) are deposited. Early in disease the distal airways are usually spared but become involved as the disease progresses.
What is asbestos?
Asbestos is a generic term for a large number of naturally occurring magnesium silicate fibres. The most important type is chrysotile - white asbestos. Crocidolite - blue asbestos - and amosite - brown asbestos - are now not used in many countries but are found as contaminants of chrysotile.
What occupations are particularly prone to asbestos exposure?
- production of cement products
- insulation materials
What are asbestos bodies?
These are mineral fibres coated with a golden-brown glycoprotein rich in iron. They are dumb-bell shaped and are identified in tissues as the hallmark of asbestos exposure.
What are the pathological effects of asbestos?
The effect of asbestos exposure depends on a number of factors most importantly the degree of exposure. This is because asbestos damage is dose dependent. The effects of asbestos exposure usually take many years to manifest - i.e. up to 30-40 years.
Light exposure results in pleural thickening, pleural calcification and mesothelioma.
Heavy exposure results in asbestosis, carcinoma and bronchial carcinoma (especially in smokers).
What is asbestosis?
This is a pneumoconiosis in which diffuse pulmonary fibrosis develops due to prolonged asbestos exposure.
The clinical features are similar to other interstitial lung diseases (e.g. progressive dyspnoea, dry cough, bibasal fine crackles, clubbing etc). Chest x ray shows bilateral reticulonodular shadowing.
Macroscopically there is slowly progressive interstitial fibrosis which starts at the lung bases where it is most marked subpleurally. The fibrosis spreads centrally and eventually causes honeycomb lung.
What is asbestosis associated with?
Patients with asbestosis are at a substantial risk of developing lung cancer. The malignancy develops in areas of fibrosis and adenocarcinoma is the most common type.
What are the pleural plaques that develop in asbestos?
These are often visible as an incidental finding on chest x rays of patients who have been exposed to asbestos.
They are bilateral, well circumscribed, white raised plaques of hyaline collagen that usually sit on the parietal pleura. When seen face on they form an irregular "holly-leaf" pattern.
What is the effect of pleural plaques?
Pleural plaques do not affect respiratory function but are markers for asbestos exposure.
This occurs many years after exposure to asbestos. Patients may present with pleuritic chest pain, and pleural effusions with blood stained exudate (even without malignancy)....
Pleurisy and pleural effusions often develop many years after asbestos exposure.
ESR is also raised. Other causes of a pleural effusion need to be excluded. Pleural biopsy shows evidence of non specific inflammation and fibrosis.
Spontaneous resolution is common but persistent effusions may lead to pleural thickening.
Pleural thickening is usually present in what area of the lung?
This is localised or diffuse thickening of the pleura that may develop as a result of asbestos exposure. There may be a history of repeated episodes of pleurisy (although these may be subclinical). It is commonly seen in associated with pleural plaques.
Thickening is most marked in the bases of the lung with obliteration of the costophrenic angle.
What are the other x ray features of pleural thickening in asbestos exposure?
Areas of fibrous strands extending from the pleura may give the appearance of "crows feet" on x ray.
Rolled up atelectasis is another feature. This is a rounded opacity that is caused by puckering of the lung by the thickened pleura.
What is mesothelioma?
This is a malignant tumour of the pleura that is associated with asbestos exposure in at least 90% of cases. It is most commonly associated with blue asbestos.
What are the presenting features of mesothelioma?
It usually presents with pain, dyspnoea, weight loss, weight loss and features of pleural effusion.
What are the radiographic features of mesothelioma on X ray and CT?
On X ray mesothelioma often appears as lobulated pleural masses encasing the lung and moving towards the hila.
CT scan often shows nodular pleural thickening encasing the lung and involving the mediastinal pleura.
What are the treatment options for mesothelioma?
As the tumour progresses it involves the pericardium and peritoneum giving rise to blood borne metastases.
Treatment options include:
1) Extrapleural pneumonectomy - only possible in a small number of cases; poor success rate
2) Radiotherapy - reduces risk of metastases; may relieve pain
3) Chemotherapy - drugs such as pemetrexed and cisplatin results in tumour shrinkage in about 40% of patients
Overall prognosis is poor and most patients die within 2 years of diagnosis
What is Byssinosis?
This is a specific form of occupational asthma caused by inhalation of cotton or flax dust. Symptoms usually occur after several years of working in the industry and and show a characteristic pattern that is distinct from normal occupational asthma.
What is unusual about the clinical features of byssinosis?
Unlike normal occupational asthma workers complain of chest tightness and dyspnoea on a Monday (the first shift of the week) and peculiarly symptoms improve throughout the week.
The exact reason for this pattern of symptoms is unclear. There is sometimes a fall in FEV1 during the working day but FEV1 poorly correlates with symptoms.
What kind of respiratory defect is associated with popcorn workers lung?
This is a relatively new occupational lung disease and it highlights an important point that not all occupational lung diseases produce interstitial lung pathology.
Popcorn workers lung is obliterative bronchiolitis due to inhalation of a ketone that gives popcorn its butter flavour. The patient develops progressive cough, breathlessness and wheeze, with fixed airways obstruction.
What is the pathogenesis of coal miners pneumoconiosis?
Coal dust inhaled into the alveoli is taken up by macrophages that are then cleared by the lymphatic system or mucociliary escalator.
If there is prolonged exposure to dust the clearance mechanisms are overwhelmed and dust macules arise particularly in the respiratory bronchioles.
Release of dust from dying macrophages induces fibroblast proliferation and fibrosis.
Is coal miners pneuomoconiosis a single disease entity?
No. An important distinction must be made between the 2 major categories of coal miners pneumoconiosis:
1) Simple coal miners pneumoconiosis
2) Complicated coal miners pneumoconiosis
What is simple coal miners pneumoconiosis?
This is the accumulation of small aggregations of coal dust that are uniformly dispersed and evident on chest x ray as reticulonodular shadowing or mottling.
Importantly, simple coal miners pneumonoconiosis is NOT associated with any significant symptoms, signs, impairment of respiratory function or alteration of prognosis or life expectancy.
It is easy to attribute respiratory symptoms to coal exposure but it is more likely to be cause by other pathologies - e.g. COPD, asthma or heart disease.
What is complicated coal miners pneumoconiosis?
This is also called progressive massive fibrosis. It is characterised by the presence of large black fibrotic masses on the lung parenchyma consisting of coal dust and bundles of collagen.
These are situated in the upper zones and appear as bizarre opacities on x ray against a background of simple pneumoconiosis.
Cavitation of these lesions can often occur and may result in the expectoration of black sputum (melanoptysis).
What is Caplan's syndrome?
Coalworkers with rheumatoid arthritis may develop multiple nodules in the lung. These are often accompanied by subcutaneous rheumatoid nodules.
What professions are at an increased risk of silicosis?
(silicosis is a type of pneumoconiosis caused by exposure to silicon dioxide)
- building tunnels and sinking shafts
- boiler scaling
- pottery industry
What is the difference between simple and complicated silicosis?
Like simple coal miners pneumoconiosis, simple silicosis causes no symptoms and is an X ray phenomenon.
Complicated silicosis results in massive, progressive fibrosis, loss of lung function and breathlessness.
What is associated with silicosis?
Patients with silicosis are at an increased risk of tuberculosis because the silica interferes with the macrophages ability to phagocytose mycobacterium.
Patients with silicosis are also at an increased risk of lung cancer.
What is the classic x ray appearance of silicosis?
A typical x ray shows reticulonodular opacities particularly affecting the upper lobes.
The nodules are usually denser and larger than those seen in coal miners pneumonconiosis. Egg shell calcification of the hilar lymph nodes is a particularly striking feature. Pleural thickening may also occur.