Chest ImagingGiant cell interstitial pneumonia
hypersensitivity reaction to inhalation of particles of hard metal. Hard metal is a material composed predominantly of tungsten carbide (WC) and cobalt (Co). Hard-metal lung disease occurs mainly in workers engaged in the manufacture of hard metal, but also in workers engaged in resharpening hard metal tools (saws, drilling tips, etc.). Hard metal lung is sometimes labelled as cobalt lung, because cobalt is probably the critical offending agent in hard metal and because the same disease has also been described in diamond polishers who use polishing disks made of diamond cobalt (i.e. not really hard metal).
Unlike most other mineral pneumoconioses, hard-metal lung does not appear to be caused principally by the reaction of excessive dust accumulation in the lungs, but it presents many features of a hypersensitivity reaction. Consequently, hard-metal lung may occur in young subjects with relatively short exposure histories. It may present (sub)acutely, with work-related clinical and radiological features similar to those of hypersensitivity pneumonitis (extrinsic allergic alveolitis). However, hard metal lung differs from hypersensitivity pneumonitis in its pathology, which is characterized by the presence in the lung interstitium and the alveolar spaces (and hence in the bronchoalveolar lavage) of 'bizarre' multinucleated giant cells with 'cannibalistic' features. The finding of such cells leads to a diagnosis of giant cell interstitial pneumonia, which is considered pathognomonic for hard-metal lung. However, the absence of giant cell interstitial pneumonia does not rule out hard metal lung. A more insidious progression may also lead to more chronic presentations with interstitial pulmonary fibrosis, resembling, in some cases, that of mixed dust pneumoconiosis.
The radiological features of hard-metal lung are nonspecific. In its subacute stages, there may be bilateral micronodular, reticular or nodular opacities, as well as ground-glass appearances. In the chronic stage, fibrosis with honeycombing may be found.
JV