Introduction

Diffuse lung disease (DLD) is a term that embraces a wide variety of disorders characterized by inflammation, damage and fibrosis in the acinar regions of the lungs. Formerly known as interstitial lung disease, the new term more properly embraces the concept that the pathological process can involve the air space as well as the interstitium. Strategies to improve understanding and treatment of these diseases have become clearer over recent years because of a better understanding of their molecular basis and clinicopathophysiological definition. Two areas in which significant advances have been made are molecular genetics (that will inform molecular epidemiological approaches – genotype) and the effects of new imaging and other technologies in diagnostic protocols (that have improved disease pattern recognition – phenotype).

Genotype

There are over 200 specific diffuse lung diseases including those characterized by granulomatous and fibrosing histopathology. The aetiology of some of these diseases is known, whereas for others it is not. For example, occupational exposure to beryllium can cause a chronic granulomatous disease that is clinically and histologically indistinguishable from sarcoidosis. A disease resembling cryptogenic fibrosing alveolitis (CFA) can be caused by exposure to asbestos, and exposure to cobalt may cause interstitial pneumonia and fibrosis. Other agents that are known to produce diffuse lung disease include some therapeutic drugs and radiation. General environmental risk factors for diseases of unknown aetiology have been identified, including exposure to dusts, cigarette smoking, sex, age and race [1, 2]. For example, systemic sclerosis occurs predominantly in females (9:1; female:male) whereas sarcoidosis occurs predominantly in the 30–40 year age range and is more aggressive in patients of Afro-Caribbean descent than in Caucasians.