Describe silicosis with its complications and prevention.

Silicosis

• The occupations at risk, which should be listed since the diagnosis depends on recognising them — stone quarrying, cutting and crushing; mining of all kinds; sandstone and slate work; agate grinding, notably in Khambhat in Gujarat; slate pencil manufacture in Mandsaur, Madhya Pradesh; GEM cutting and polishing; foundry work, particularly sand blasting and fettling; pottery and ceramics; glass manufacture; construction, tunnelling and stone crushing; and sand blasting, which is among the most intensely exposing of all processes
• The agate and slate pencil industries deserve naming because they are small-scale, unregulated, home-based and have produced entire villages of affected workers, illustrating the unorganised-sector problem in its clearest form
• The pathogenesis — respirable silica particles of 0.5 to 5 micrometres reach the alveoli, where they are engulfed by macrophages
• Silica is cytotoxic and kills the macrophage, which releases inflammatory mediators and fibrogenic factors, and the liberated silica particle is then taken up by another macrophage, repeating the cycle
• That self-perpetuating cycle explains the most important clinical fact about silicosis — the disease progresses even after exposure has ceased entirely, because the silica remains in the lung and continues to kill macrophages
• The result is the silicotic nodule, a whorled, concentric, hyalinised collagenous lesion, chiefly in the upper zones and in the hilar lymph nodes
• The clinical types:
• Chronic (classical) silicosis — after 10 to 20 years of moderate exposure, the commonest form
• Accelerated silicosis — after 5 to 10 years of heavier exposure
• Acute silicosis (silicoproteinosis) — after months to a few years of very intense exposure, as in sand blasting; it is rapidly progressive and frequently fatal
• The existence of an acute form matters practically, since a young worker with rapidly progressive breathlessness and a short employment history may still have silicosis, and the diagnosis is missed if a long latency is assumed
• Clinical features — insidious exertional dyspnoea; dry cough; chest tightness; and later respiratory failure and cor pulmonale
• The early stages are asymptomatic with a normal examination, which is why the diagnosis depends on radiography and on exposure history rather than on symptoms
• Radiology — small rounded opacities predominantly in the upper zones; egg-shell calcification of the hilar lymph nodes, which is characteristic though not universal; and, in advanced disease, progressive massive fibrosis with large conglomerate masses and distortion of the lung
• The complications:
• Tuberculosis (SILICO-tuberculosis) is by far the most important, since silica impairs macrophage function, which is precisely the cell that contains mycobacteria
• The risk of tuberculosis in a silicotic worker is many times that of an unexposed person, and remains elevated even after exposure ends
• The practical consequences are direct — screen every silicotic worker for tuberculosis regularly; consider TB preventive therapy; and suspect tuberculosis in any silicotic whose condition deteriorates or whose radiograph changes
• Radiological diagnosis of tuberculosis is difficult against a background of silicotic shadowing, so bacteriological confirmation matters more here than usual
• Other complications — progressive massive fibrosis; cor pulmonale; pneumothorax; increased risk of lung cancer, silica being classified as a human carcinogen; chronic bronchitis and emphysema; and autoimmune conditions including scleroderma and rheumatoid arthritis
• Management — there is NO specific treatment and NO measure that reverses the fibrosis
• It consists of — removal from further exposure; aggressive detection and treatment of tuberculosis; smoking cessation; vaccination; bronchodilators, oxygen and pulmonary rehabilitation; and compensation and rehabilitation to alternative work
• Prevention is therefore everything, and follows the hierarchy — substitution of silica-free abrasives for sand in blasting, which many countries have made compulsory; wet methods of drilling, cutting and grinding, which suppress dust at source; enclosure and local exhaust ventilation; dust monitoring; respirators as a supplement only; pre-placement and periodic radiography; and worker education and awareness
• Wet drilling is the single most effective and cheapest measure in Indian quarries, and its absence is usually a matter of cost and habit rather than of technical difficulty
• Silicosis progresses after exposure stops, since the released silica is engulfed again in a self-perpetuating cycle
• Silica disables the macrophage, which is exactly the cell that contains mycobacteria, hence the tuberculosis risk
• Screen every silicotic worker for tuberculosis, and suspect it whenever the condition or the film deteriorates
• Egg-shell hilar calcification is characteristic, alongside upper zone rounded opacities
• Acute silicosis follows months of intense exposure, so a young worker with a short history may still have it
• Wet drilling is the cheapest effective measure, and its absence is usually habit and cost rather than technical difficulty
• Substitute silica-free abrasives for sand in blasting, which several countries have made compulsory
• Agate and slate pencil work produced whole affected villages, which is the unorganised-sector problem in its clearest form
• Early disease is asymptomatic with a normal examination, so diagnosis rests on radiography and exposure history
• Confirm tuberculosis bacteriologically here, since radiology is unreliable against a silicotic background