OCCUPATIONAL LUNG DISEASE

by Dr Jeremy R Beach MD, MRCP, MFOM, Senior Lecturer and Honorary Consultant, University of Birmingham and Birmingham Chest Clinic

Occupational lung diseases have been with us for many years but they have been attracting particular attention in recent years. This is due to a growing public emphasis on the responsibilities of business and to new authoritative publications resulting from the Surveillance of Work-related and Occupational Respiratory Disease (SWORD) project in the UK and similar schemes overseas.

Occupational lung disease should be entirely preventable and it is disappointing that it apparently continues to increase.

Prevalence of occupational lung disease

Data on the prevalence of occupational lung diseases are available from a number of different sources. Reporting schemes such as SWORD collate and publish data provided by chest physicians and occupational physicians (Box 1).(1-3) There are also local initiatives in the UK and in some overseas countries.

Occupational asthma is the single most frequently reported disease, but patients with asbestos-related diseases (nonmalignant pleural disease and mesothelioma) constitute a larger group. Patients with the pneumoconioses are also common. Data from Canada suggest that other industrialised countries probably have similar patterns of disease,(4) although pneumoconiosis may be a greater problem in developing countries.

However, voluntary reporting schemes such as SWORD may not give a comprehensive picture because of incomplete recognition, referral, and reporting of cases. Additional data from other sources may help to give a more complete idea of prevalence. These sources include the Reporting of Injuries Diseases and Dangerous Occurrences Regulations (RIDDOR), which require employers to report cases of work-related disease to the Health and Safety Executive, and disability benefit claims for prescribed diseases. Both these report considerably fewer cases than SWORD, and it is likely that they, too, underestimate the numbers of patients with occupational lung disease.(3)

In addition, information is available from the 1990 Labour Force survey, and the 1995 Self-reported Work-related Illness survey (SWI 95) on the prevalence of self-reported occupational lung diseases.(5,6) Unsurprisingly, the estimates of the prevalence of disease from these sources exceed those generated by doctor-based reporting schemes. SWI 95 estimated that 202,000 people in Great Britain were suffering a work-related respiratory illness, of whom 151,000 had asthma symptoms, 83,000 chronic bronchitis symptoms, and an estimated 19,000 had pneumoconiosis.

The other major sources of data are the numerous published studies based on surveys of workers in particular occupations. For example, surveys of laboratory animal workers have reported a prevalence of work-related asthma of approximately 10%,(7-9) and a similar prevalence has been reported among bakers.(10,11) Such studies generally suggest a higher incidence of disease than do the data reported to SWORD.

How occupational lung disease presents

Patients with occupational lung disease generally present with similar symptoms and signs to patients with nonoccupational disease. Thus, patients with occupational asthma usually present with episodes of breathlessness and chest tightness, often accompanied by cough. Patients with work-related lung cancers usually present with haemoptysis, breathlessness, systemic symptoms, and signs of consolidation or collapse. Work-related bronchitis is defined by the presence of cough and sputum; and occupational allergic alveolitis commonly presents in the same way as allergic alveolitis related to causes outside of work, with breathlessness and cough, sometimes accompanied by systemic symptoms.

Patients with mesothelioma most commonly present with chest pain - sometimes also with cough and breathlessness - which may or may not be accompanied by signs of a pleural effusion. This combination should alert GPs to the possibility of mesothelioma, particularly in a poorly patient with systemic symptoms and signs.

Making the diagnosis

It is important to distinguish between occupational and nonoccupational causes of lung disease.

Symptoms and signs

Only a few of the occupational lung diseases are so specific to occupational causes that work is immediately obvious as the cause.

Mesothelioma is perhaps the most striking example of a disease that is work-related in the majority of cases in the UK. The pneumoconioses are also usually work-related, although the symptoms and signs of pneumoconiosis can be easily mistaken for other types of pulmonary fibrosis. However, in many cases, nonoccupational causes of disease may initially appear more likely, and a smoker is liable to have his or her cough and sputum attributed to smoking rather than the job in most cases.

Practice nurses are increasingly taking a role in caring for patients with asthma and other respiratory conditions. As they may be consulted by patients with new or worsening symptoms, it is important that they, too, are alert to the possibility of work-related respiratory disease.

The key to making the connection between work and disease lies in the combination of a high index of suspicion and in taking a detailed occupational history. For example, suspicion should be aroused by any adult patient in work developing new or worsening asthma, and a work-related cause should be considered. A work history must go back to the time the patient left school or college because many lung diseases may have a prolonged latent period. Mesothelioma commonly occurs more than 40 years after exposure to asbestos, and lung cancer may occur more than 20 years after exposure.

The work history must contain sufficient detail to identify possible causes of disease. Job titles such as 'jigger', 'caulker', or 'fettler' will be unfamiliar to many doctors and yet the work may entail exposure to a number of potentially hazardous agents. Job titles such as 'works engineer' or 'maintenance engineer' should also prompt further enquiry as such jobs may involve exposure to a wide variety of hazards - often when the usual precautions for controlling exposure are relaxed to allow access.

Even well-informed patients with good memories may not know enough about the agents they have worked with to allow an occupational cause to be excluded with confidence, and sometimes further information from employers or suppliers of chemicals will be needed. A 'material safety data sheet' summarising some of this information should be available for all chemicals in use in any workplace, but they are sometimes incomplete or inaccurate.

Jobs which carry an increased risk of occupational asthma are listed in Box 2, and the prescribed causes of occupational asthma (ie those for which disability benefit is payable) are given in Box 3. Some known and suspected causes of occupational lung cancer are given in Box 4.(12-14)

The relation between exposure and the onset of symptoms may hint at an occupational cause in some diseases. In allergic alveolitis, asthma, reactive airway dysfunction syndrome and some other diseases, symptoms may occur within a few minutes of exposure and this helps greatly in identifying the role of work, and in some instances even the specific agent responsible. When the response is less immediate, the relation is harder to recognise. For example, where agents cause only a late asthmatic reaction, symptoms may be maximal only after the patient has gone home. Consequently, the best question to ask when seeking a relation between workplace exposures and disease is not whether symptoms are worse at work but whether they are better on days away from work. It is also worth remembering that some patients require a considerable time away from work before their symptoms improve. Therefore it is worth asking about improvement on holiday, although a positive answer may point towards other environmental factors than work.

Tests of lung function

Tests of lung function are useful in diagnosing lung diseases but in general are of little help in discriminating between those with and those without occupational causes. Abnormalities of lung function are usually similar regardless of the cause. Thus, occupational asthma will tend to show an obstructive pattern on lung function testing; emphysema in coal miners will often show a combination of airflow obstruction, hyperinflation, and abnormal gas transfer; while the pneumoconioses classically show a restrictive pattern on lung function testing. However, this is something of an over-simplification and in asbestosis there may be both restriction and obstruction.

Because occupational asthma is reversible - and to some extent so are some of the other airway diseases - techniques have been developed for repeated measurement of lung function throughout the day to attempt to relate changes in lung function to exposure. The most frequently used is serial peak flow measurement. Patients are asked to record peak flow every 2 hours while at work and away from work over a period of 4-6 weeks or longer and then the maximum, mean and minimum peak flow measurements are plotted for each day. These were recorded by a scenery manufacturer who used epoxy resin and isocyanate-based resin and paint systems, and appear to show a clear work-related effect. Other measurements such as forced expiratory volume in 1 s (FEV1) may also be performed repeatedly although the equipment required is often less portable than a peak flow meter.

Chest x-rays

Chest x-rays are generally considered the definitive investigation for diagnosing pneumoconioses, but may also be useful in diagnosing other diseases such as lung cancer or allergic alveolitis. To be of maximum value, they need to be performed to accepted standards and properly interpreted. For the pneumoconioses, a classification devised by the International Labour Office (ILO) is usually used to describe the extent and severity of radiological changes - these, however, may be only loosely related to symptoms and disability.

Tests for sensitisation

These include skin prick tests and measurements of specific antibodies to agents encountered at work. A wide variety of allergens can now be tested for - this is particularly useful in diagnosing occupational asthma, but may also be useful for allergic alveolitis (farmer's lung, mushroom picker's lung, etc). Interpretation of the results is not always straightforward as antibodies may be a marker for exposure rather than disease, and it is not yet possible to test for antibodies for all substances that may be encountered at work. However, when a test is available, a positive skin prick test or the presence of specific antibodies confirms exposure and suggests that sensitisation has occurred, providing supportive evidence that a particular agent is the cause of the disease.

Bronchial challenge tests

Measuring nonspecific airway responsiveness, usually to histamine or methacholine, is a useful additional test of lung function in suspected asthma. Although many different techniques are used they all measure a patient's tendency to develop bronchoconstriction, which is closely related to asthma. Nonspecific airway responsiveness can be measured if asthma is suspected, and if measured before and after exposure to a suspected cause of asthma, can confirm that the underlying disease is worsening.

Specific bronchial challenge tests to agents encountered at work are the most accurate way of diagnosing occupational asthma. However, they can be complex - it is simple enough to ask a patient suspected of having asthma caused by solder flux fume to solder in a controlled environment for a short period and measure lung function over the following 12-24 hours, but the difficulty lies in selecting a dose sufficient to precipitate a mild but not severe asthmatic response. Tests of this type are liable to misinterpretation and, because they carry a small risk to patients, should only be carried out in centres with the correct expertise.

Management of occupational lung disease

In general, occupational lung diseases are managed in a similar fashion to their nonoccupational counterparts. The exception to this is that, where possible, further exposure to the causative agents should be minimised or prevented. In occupational asthma, continuing exposure results in a bad prognosis, perhaps through long-term accelerated loss of lung function. Although there is not the same weight of evidence in other diseases, it seems logical to reduce exposure to prevent further damage.(15,16)

Referral to a specialist clinic may be helpful in the diagnosis and management of some patients and there are now several clinics specialising in occupational lung diseases around the country - addresses of some of these are given at the end of this article. Such specialist clinics - and other respiratory medicine clinics - can also provide sequential measurements of lung function to indicate whether accelerated loss of lung function is occurring through continuing inadvertent exposure.

In addition to clinical management, other actions specific to occupational diseases should be considered. Diseases of this type must be reported under RIDDOR to the Health and Safety Executive (HSE), although it is the employer rather than the doctor who is responsible.(17) The doctor diagnosing a work-related disease is responsible for informing the employer, but there is a possible conflict over preserving the confidentiality of the patient. Obviously, an employer must be given information - which is usually considered confidential - before they can report a case to the HSE. The GP should discuss this with the patient as they are often initially reluctant to inform their employer, and it is difficult to prevent further exposure without telling the employer of your suspicions. Alternatively, the HSE is usually prepared to accept reports directly from doctors, and they do have a number of medical inspectors within the Employment Medical Advisory Service (EMAS) with whom you can discuss suspected cases while maintaining confidentiality.

Medical inspectors are usually happy to discuss individual cases and how they may be investigated further without the employee's or employer's name being disclosed. Patients with a work-related disease may also contact the HSE themselves and are then usually asked if the complaint can be disclosed to their employer or if they wish to remain anonymous. However, investigation of a suspected case of occupational lung disease by the HSE often leads to the identity of the patient becoming known to the employer at some point.

Liaising with employers about a suspected case of occupational lung disease presents a number of problems but can be invaluable in helping the patient. Employers can provide information about workplace exposures, and they have the power to change the patient's job so that he or she is no longer exposed to an agent suspected of causing harm. Employers may also need to introduce further controls on exposure of other workers to the same agent.

Many employees, however, fear victimisation by their employer, and there is some evidence that many patients with occupational lung disease do become unemployed.(16,18) Some larger employers may have an occupational health service and it is possible to discuss a suspected case of occupational lung disease with them while maintaining the confidentiality of the patient, and with some reassurance that the patient will not be victimised. Some patients may be reluctant to allow even this contact as they are often mistrustful of employers' occupational health services. It is worthwhile discussing the options with the patient, as the best outcome often occurs where an employee and employer can work together to ensure further exposure is minimised or prevented while the patient remains in employment. However, this ideal outcome is achieved relatively infrequently.

It is worth informing the patient that they may be entitled to seek compensation for their disease in the form of a claim for disability benefit, or a claim against their employer for damages. There are usually other sources of advice where they can find out more about these options, such as the Department of Social Security, the Citizens Advice Bureaux, their trade union or a local solicitor. Neither option is straightforward, and neither is likely to make them rich.

Conclusion

Occupational lung diseases continue to cause considerable mortality and morbidity despite the fact that they are all preventable. They present in ways similar to their nonoccupational counterparts and distinguishing occupational from nonoccupational disease can be difficult. Management, too, is similar to the management of nonoccupational diseases except that in most cases additional steps should be taken to avoid further exposure and a poorer prognosis. Reporting to the HSE, other reporting schemes, and aspects of compensation also need to be considered. Liaising with employers can be difficult because of problems with confidentiality and fears of victimisation, but can be the best way of identifying causes in the workplace and bringing about change to reduce future risks for both the patient and colleagues. Where an employer has an occupational health service this can help avoid problems with liaison. There are a number of specialist clinics that can help with making the diagnosis and subsequent management.

Box 1. Incidence of occupational lung diseases reported to SWORD 1992-1996.

• Disease Year - 1992 1993 1994 1995 1996
• Allergic alveolitis 97 11 446 20 67
• Asthma 1047 879 941 851 1136
• Bronchitis 133 58 38 50 38
• Building-related 11 22 8 - -
• Byssinosis 4 6 1 - -
• Infections 53 37 59 31 136
• Inhalation accidents 251 283 280 353 207
• Lung cancer 146 6 470 62 111
• Mesothelioma 723 64 464 4487 496
• Nonmalignant pleural 681 736 730 590 556
• Pneumoconiosis 418 349 341 172 364
• Other 71 77 109 125 211
• Total 3635 3269 3267 2741 3322

Box 2. Some occupations with an increased risk of occupational asthma.(12)

• Occupation Incidence (per million/year)
• Spray painters 756
• Chemical processors 728
• Plastics processors and manufacturers 454
• Metal treatment 344
• Welders and electronic assemblers 301
• Bakers 290
• Laboratory workers 268
• Other food processors 149

Box 3. Prescribed causes of occupational asthma in the UK.

• Isocyanates
• Acid anhydride and amine hardening agents
• Proteolytic enzymes
• Grain dust or flour
• Cimetidine
• Isphaghula
• Ipecacuanha
• Glutaraldehyde
• Crustaceans or fish
• Soya bean
• Green coffee bean dust
• Platinum salts
• Rosin/colophony as a soldering flux
• Laboratory animals and insects (some use on farms is also included)
• Antibiotics
• Wood dusts
• Castor bean dust
• Azodicarbonamide
• Persulphate salts of henna
• Reactive dyes
• Tea dust
• Fumes from stainless steel welding and any other sensitising agent inhaled at work

Box 4. Some known and suspected causes of occupational lung cancer.

• Cause, Agent Process, Known causes
• Asbestos Mining, milling, use (insulation, shipyards)
• Arsenic Metal smelting, pesticides
• Chloromethyl ethers Chemical production workers
• Chromium Chromate production, pigment manufacture
• Ionising radiation, radon Uranium mining, other mining
• Mustard gas Manufacture
• Nickel Nickel mining, refining, plating
• Polycyclic aromatic Coke oven workers, rubber workers, aluminium hydrocarbons, smelters

Suspected causes

• Acrylonitrile Plastics, petrochemicals, textile production
• Beryllium Beryllium extraction, production and processing
• Cadmium Smelting, battery production
• Formaldehyde Formaldehyde production and use (preservatives, resins)
• Silica Mining
• Synthetic mineral fibre Manufacture and use as insulation
• Vinyl chloride monomer PVC and plastic production

Practical points

• Occupational asthma, asbestos-related diseases and pneumoconioses are the most common occupational lung diseases.
• Occupational lung disease presents with similar symptoms and signs to its nonoccupational counterpart. Mesothelioma is a little different and commonly presents with chest pain, with or without a pleural effusion
• Many occupational lung diseases have a prolonged latent period - mesothelioma commonly occurs 40 years after exposure to asbestos.
• In allergic alveolitis, asthma and reactive airway dysfunction syndrome symptoms may occur within a few minutes of exposure and this helps in identifying work as the cause.
• A chest x-ray is the definitive investigation for diagnosing pneumonocioses.
• Specific bronchial challenge tests are the gold standard for diagnosing occupational asthma.
• Occupational lung diseases are managed in a similar fashion to their nonoccupational counterparts.
• The doctor diagnosing a work-related disease is responsible for informing the patient's employer.

References

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