Occupational lung disease overview

# Overview
Occupational lung diseases have long been described since the Egyptian and Roman empires existed. Dr. Benardino Ramazzini, described as the "father of occupational medicine" was first to coin the term "disease of workers" in the 17th century. Occupational lung disease may be classified according to the type of inhalant into 3 groups: inorganic dust, organic dust, and agents other than inorganic and organic dust.As the particles accumulate, the body's elimination mechanisms begin to fail, resulting in activation of chemotactic factors that exacerbate the inflammatory response, and subsequently lead to fibrosis. Occupational lung disease may be caused by organic dust such as thermophilic and true fungi, and bacteria and animal proteins, or by inorganic dust such as, silicates, carbons and metals, or by agents other than organic or inorganic dusts such as, chemicals, gases, fumes, vapors and aerosols. Incidence, prevalence and mortality rates for occupational lung disease are not well documented and are unreliable.  Disease manifestation is correlated to the frequency, duration and dose of inhalational exposure. Occupational lung disease has no predilection to race or gender, however, males tend to work in environments where exposure is common, therefore more males suffer from occupational lung disease. Occupational lung disease, particularly, coal worker's pneumoconiosis is a common disease that tends to affect coal miners in West Virginia and Kentucky, USA and South Wales, UK. Common risk factors in the development of occupational lung disease include smoking, genetic susceptibility, cardiovascular disease, and frequency, intensity and duration of exposure. If left untreated, patients with occupational lung disease may progress to develop pleural effusion, interstitial lung fibrosis, and lung cancer. Common complications of of occupational lung disease include interstitial pulmonary fibrosis, progressive massive fibrosis, mesothelioma, and premature death. The initial study of choice for the diagnosis of occupational lung disease is a chest x-ray. The findings on x ray that are suggestive of occupational lung disease include, pleural thickening, plaques, calcifications, opacities and atelectasis. A positive history of occupational exposure to a particular agent with progressive worsening of respiratory symptoms including dyspnea, cough and fatigue. The most common symptoms of occupational lung disease include cough, shortness of breath, and wheezing.  Physical examination of patients with occupational lung disease is usually remarkable for bronchial breathing, increased vocal resonance, and fine crepitations.  A chest x-ray is the cornerstone of diagnosis in occupational lung disease. Findings on an x-ray suggestive of occupational lung disease include pleural thickening, pleural plaques, pleural abnormalities, calcification, small or large opacities, costophrenic angle obliteration, atelectasis, pneumothorax, parenchymal bands, enlarged hilar or mediastinal lymph nodes, bullae and granulomata. A high resolution chest CT scan or "thin-section" CT may be helpful in the further diagnosis of occupational lung disease. Findings on CT scan suggestive of occupational lung disease include nodules with sharp margination, opacities, lymph node hyperplasia and egg shell calcification, and interlobular septal thickening and intralobular lines. The mainstay of treatment for occupational lung disease is medical therapy. Surgery is usually reserved for patients with progressive massive fibrosis or lung cancer. Effective measures for the primary prevention of occupational lung disease include the prevention of smoking and smoking cessation, health awareness, and routine surveillance. Certain materials have been abolished from use in industry such as asbestos. Also reducing exposure through the use of medical masks and respirators, robots, isolation of harmful processes, ventilation, limiting exposure hours, maintenance of dust control systems, and the use of warning signs.

# Historical Perspective
Occupational lung diseases have long been described since the Egyptian and Roman empires existed. The 10th century to the 18th century demonstrated the largest period of industrial mechanization and infrastructure, this led to the awareness and advent of occupational health hazards and sciences. These movements led to the rising need for trade unions and workers' legislation. Dr. Benardino Ramazzini, described as the "father of occupational medicine" was first to coin the term "disease of workers" in the 17th century. Later in the 20th century , Dr. Alison Hamilton became a leading expert in occupational health.

# Classification
Occupational lung disease may be classified according to the type of inhalant into 3 groups: inorganic dust, organic dust, and agents other than inorganic and organic dust.

# Pathophysiology
Occupational lung diseases include the pneumoconioses (interstitial lung diseases), hypersensitivity pneumonitis, bronchiolitis, byssinosis, and occupational asthma. Pneumoconiosis is an interstitial lung disease caused by the accumulation of different dust particles in the alveolar space. As the particles accumulate, the body's elimination mechanisms begin to fail, resulting in activation of chemotactic factors that exacerbate the inflammatory response, and subsequently lead to fibrosis. Hypersensitivity pneumonitis or extrinsic allergic alveolitis and its subcategories of,  bronchiolitis, bysinnosis and occupational asthma are all part of the respiratory systems over reactivity towards inhalants.

# Causes
Occupational lung disease may be caused by organic dust such as thermophilic and true fungi, and bacteria and animal proteins, or by inorganic dust such as, silicates, carbons and metals, or by agents other than organic or inorganic dusts such as, chemicals, gases, fumes, vapors and aerosols.

# Differentiating occupational lung disease from Other Diseases
Occupational lung disease must be differentiated from other diseases that cause shortness of breath, cough, and wheeze, such as allergic asthma, emphysema, sarcoidosis, tuberculosis, and chronic bronchitis.

# Epidemiology and Demographics
Incidence, prevalence and mortality rates for occupational lung disease are not well documented and are unreliable. Individual occupational lung diseases have separate prevalence and incidence rates, such as, farmer's lung has an incidence of 270 cases per 100,000 in 2012. Whilst the mortality rates for work-related disease are approximately 63,000 deaths in 2012. Disease manifestation is correlated to the frequency, duration and dose of inhalational exposure. Occupational lung disease has no predilection to race or gender, however, males tend to work in environments where exposure is common, therefore more males suffer from occupational lung disease. Occupational lung disease, particularly, coal worker's pneumoconiosis is a common disease that tends to affect coal miners in West Virginia and Kentucky, USA and South Wales, UK.

# Risk Factors
Common risk factors in the development of occupational lung disease include smoking, genetic susceptibility, cardiovascular disease, and frequency, intensity and duration of exposure.

# Screening
There is insufficient evidence to recommend routine screening for occupational lung disease at a national level, however, at a local level workers with known occupational hazards benefit from a routine screening at their places of work.

# Natural History, Complications, and Prognosis
If left untreated, patients with occupational lung disease may progress to develop pleural effusion, interstitial lung fibrosis, and lung cancer. Common complications of of occupational lung disease include interstitial pulmonary fibrosis, progressive massive fibrosis, mesothelioma, and premature death. Depending on the extent of the disease progression at the time of diagnosis, the prognosis may vary. However, the prognosis is generally regarded as poor.

# Diagnosis

## Diagnostic Study of Choice
The initial study of choice for the diagnosis of occupational lung disease is a chest x-ray. The findings on x ray that are suggestive of occupational lung disease include, pleural thickening, plaques, calcifications, opacities and atelectasis.

## History and Symptoms
A positive history of occupational exposure to a particular agent with progressive worsening of respiratory symptoms including dyspnea, cough and fatigue. The most common symptoms of occupational lung disease include cough, shortness of breath, and wheezing. Less common symptoms of occupational lung disease include hemoptysis, weight loss, and loss of appetite.

## Physical Examination
Patients with occupational lung disease usually appear fatigued and short of breath. Physical examination of patients with occupational lung disease is usually remarkable for bronchial breathing, increased vocal resonance, and fine crepitations.

## Laboratory Findings
There are no diagnostic laboratory findings associated with occupational lung disease. However, useful laboratory findings consistent with the diagnosis of occupational lung disease include abnormal arterial blood gases, sputum analysis, and blood picture.

## Electrocardiogram
There are no ECG findings associated with occupational lung disease. However, chronic lung disease may be complicated by cor pulmonale. Findings on an ECG suggestive of cor pulmonale include, right axis deviation, R/S amplitude ratio in V1 greater than 1, R/S amplitude ratio in V6 less than 1, peaked P waves (P pulmonale in leads 2, 3, and aVF), S 1 Q 3 T 3 pattern and incomplete (or complete) right bundle branch block, and possibly, a low voltage QRS complex.

## X-ray
A chest x-ray is the cornerstone of diagnosis in occupational lung disease. Findings on an x-ray suggestive of occupational lung disease include pleural thickening, pleural plaques, pleural abnormalities, calcification, small or large opacities, costophrenic angle obliteration, atelectasis, pneumothorax, parenchymal bands, enlarged hilar or mediastinal lymph nodes, bullae and granulomata.

## Echocardiography and Ultrasound
There are no echocardiography/ultrasound findings associated with occupational lung disease.

## CT scan
Initially, the first investigation recommended to diagnose occupational lung disease is a chest x-ray. A high resolution chest CT scan or "thin-section" CT may be helpful in the further diagnosis of occupational lung disease. Findings on CT scan suggestive of occupational lung disease include nodules with sharp margination, opacities, lymph node hyperplasia and egg shell calcification, and interlobular septal thickening and intralobular lines.

## MRI
There are no MRI findings associated with occupational lung disease. However, a MRI may be helpful in distinguishing in (coal worker's pneumonconiosis) progressive massive fibrosis from lung carcinoma.

## Other Imaging Findings
PET may be helpful in the diagnosis and staging of mesothelioma. PET is also useful in distinguishing a fibrotic nodule from an actively inflamed nodule.

## Other Diagnostic Studies
Other diagnostic studies for occupational lung disease include spirometry, which distinguishes obstructive from restrictive lung disease.

# Treatment

## Medical Therapy
Supportive therapy for occupational lung disease before fibrotic disease sets in includes glucocorticoid therapy. Anti-asthmatic drugs may also be used to provide relief from dyspnea.

## Surgery
The mainstay of treatment for occupational lung disease is medical therapy. Surgery is usually reserved for patients with progressive massive fibrosis or lung cancer.

## Primary Prevention
Effective measures for the primary prevention of occupational lung disease include the prevention of smoking and smoking cessation, health awareness, and routine surveillance. Certain materials have been abolished from use in industry such as asbestos. Also reducing exposure through the use of medical masks and respirators, robots, isolation of harmful processes, ventilation, limiting exposure hours, maintenance of dust control systems, and the use of warning signs.

## Secondary Prevention
Effective measures for the secondary prevention of occupational lung disease include cessation of smoking and exposure, and routine screening including skin prick tests, questionnaires and spirometry.