Author's reply

Author's reply I am pleased to note that my old friends Gee and Morgan accept that coalminers have an excess of emphysema over the general population, although I would remind them that this was not measured and related to measured dust exposure until the work of Ruckley and colleagues.' It was, however, the early work in Morgan's laboratory which first excited my personal interest in this confusing subject. Gee and Morgan misquote Ruckley et al when they say that they showed a relation between extent (or category) of pneumoconiosis and emphysema. What was reported in that paper and confirmed in recent work was a relation between prevalence of pathological centriacinar emphysema in the lungs of a large group of coalminers and their lifetime dust exposure. This has now been confirmed in non-smoking miners.2 It is essential to my argument that this central fact is understood. This being apparently the case, there should be no difficulty in appreciating that if also decrement in FEV, is related to lifetime dust exposure and, from several unconnected studies, there is a general inverse relation between extent of centriacinar emphysema and FEV,, then it is plausible to suggest that decline in FEV, may be due to emphysema caused (at least in part) by exposure to dust. One purpose ofmy article was to give the evidence for this and to quote some supportive work on mechanisms. I am disappointed that Gee and Morgan are unimpressed with my hypothesis that injury to the lung commonly causes fibrosis and emphysema simultaneously. Certainly, many conditions present to the clinician as primarily one of these, but pathologically there is usually a minor component of the other. In silicosis of the accelerated type or silicotic progressive massive fibrosis, of which I have recently seen a surprising number of cases, emphysema is often a major component. Incidentally, the Institute of Occupational Medicine has never suggested that exposure to silica does not cause emphysema, rather that quartz in coal dust appears to reduce the strength of the relation between exposure to dust and prevalence of emphysema. This is consistent with the hypothesis that quartz is less liable to cause emphysema and more liable to cause fibrosis than coal. But the general hypothesis I have proposed is one that should be tested experimentally by those interested in the mechanisms of lung disease who, at present, seem to be divided into those studying fibrosis and those studying emphysema. My other main point related to the award of Industrial Injuries Benefit in the British context, a system ofno fault compensation very different from making a claim of injury due to an employer's negligence. In this British system, it is necessary for an employed person to show he has a prescribed disease, and my argument was concerned with a fair system for coalminers in the light of current knowledge. It was not concerned with people with disabilities due to other causes, matters open for the Industrial Injuries Advisory Council to review as and when they feel the evidence is worth considering. My suggestion is relatively simple, and recognises (as do Gee and Morgan) that coalminers are at increased risk ofemphysema. I have expressed the opinion that in the presence of radiological evidence of exposure to coalmine dust (pneumoconiosis), a reduced FEV, should be attributed to that man's dust exposure and benefit paid accordingly. This, like every other system of dividing a continuum into two, is not absolutely fair, but is the fairesi way I can think of, taking account of the scientific evidence and the law and regulations as they stand. In civil litigation such matters have to be solved by courts on the balance of probabilities, and I can see that some may argue that all airflow obstruction in miners is due to dust as others would argue that it is all due to smoking. The truth, as ever, lies somewhere between and in the case ofcoalminers I believe we have sufficient evidence to have a stab at finding a just settlement. Finally, Gee and Morgan might perhaps agree that before swallowing anything, they should look at it carefully. Some things are best swalled whole. Try crunching your antibiotics -they often taste quite bitter.