Kaolinosis

Kaolinosis is the pneumoconiosis caused by inhalation of kaolin (china clay), a hydrated aluminium silicate, Al2Si2O5(OH)4. Exposure occurs in kaolin mining, drying, and milling, and in the use of kaolin in ceramics, paper coating, paint, rubber, cosmetics and pharmaceuticals. Free silica content (usually 2 to 10 percent, and sometimes more) and the proportion of respirable particles determine the severity.

The pathological picture is a mixed dust reaction: macrophage collections, diffuse interstitial fibrosis, and in some cases nodular silicotic lesions. Simple kaolinosis rarely produces impairment. Progressive massive fibrosis can develop after 20 to 30 years of heavy exposure, and ILO profusion category 2 or higher carries a significant risk of impaired function. Mortality from non-malignant respiratory disease is increased, and tuberculosis occurs with higher frequency when silica is also present.

• Asymptomatic in simple disease with abnormal radiograph.
• Cough, sputum and exertional dyspnoea develop with progression.
• Fine basal crackles, occasionally clubbing in advanced cases.
• Large opacities (progressive massive fibrosis) cause severe breathlessness, black or grey sputum, and cor pulmonale.
• Red flags: haemoptysis, fever, night sweats and weight loss (tuberculosis), pneumothorax, rapidly progressive dyspnoea.
• Associated: chronic bronchitis, emphysema, rheumatoid pneumoconiosis (Caplan nodules), autoimmune disease.

• Occupational history including duration of clay exposure and silica content of the deposit.
• Chest radiograph: small rounded or irregular opacities (ILO category 1 to 3), mid and upper zones; progressive massive fibrosis as upper zone conglomerates over 1 cm.
• High resolution CT: centrilobular nodules, subpleural nodules, fibrosis, conglomerate masses; hilar node enlargement with eggshell calcification occasionally.
• Spirometry: normal early, mixed or restrictive later, with reduced DLCO.
• Sputum for acid fast bacilli and GeneXpert MTB/RIF when radiographic change is progressive or symptoms are systemic; HIV test.
• Lavage or biopsy showing birefringent particles, aluminium and silicon on microanalysis, when diagnosis is uncertain.
• Exclude silicosis from other sources, asbestosis, sarcoidosis, tuberculosis, and lung cancer.

• Remove from exposure when profusion category is 2 or higher, or when function declines; reduce exposure in those with minimal change. No drug removes retained dust.
• Dust control: wet processing, enclosure, local exhaust, and P3 respirators.
• Tuberculosis: treat active disease with rifampicin 150 mg, isoniazid 75 mg, pyrazinamide 400 mg and ethambutol 275 mg fixed dose combination (adult 50 to 70 kg: 4 tablets orally once daily) for 2 months, then rifampicin 150 mg and isoniazid 75 mg (4 tablets daily) for 4 months; extend to 9 months in silicotuberculosis. Pyridoxine 25 mg daily.
• Latent tuberculosis: isoniazid 300 mg and pyridoxine 25 mg orally once daily for 6 months.
• Airway obstruction: salbutamol 200 micrograms inhaled as needed; tiotropium 18 micrograms inhaled once daily.
• Respiratory failure: long term oxygen for resting PaO2 below 7.3 kPa; consider transplant referral.
• Follow up: chest radiograph and spirometry every 3 years in exposed workers, annually in those with category 1 or higher.
• Counselling: stop smoking, vaccinations (annual influenza, pneumococcal), compensation notification.