Siderosis

Siderosis is the benign pneumoconiosis caused by inhaled iron oxide dust without significant fibrogenic co-exposure. Sources include iron ore mining, iron and steel foundry work, haematite mining and polishing, and silver finishing (silver finisher's lung). Iron oxide particles are engulfed by alveolar macrophages and accumulate around bronchioles and in the interstitium. Uncomplicated siderosis produces striking radiographic change but little or no functional impairment and is reversible: opacities regress over years after exposure ceases.

Haematite miners exposed to silica as well develop siderosilicosis, which is a progressive fibrotic disease. Pulmonary siderosis must also be separated from pulmonary haemosiderosis caused by repeated alveolar bleeding, which has a very different mechanism. Excess lung cancer in haematite miners is attributed to radon and silica rather than iron.

• Usually asymptomatic and detected on a screening chest radiograph.
• Mild cough or sputum in smokers.
• Normal chest examination.
• Dyspnoea, crackles and restrictive changes suggest silica co-exposure or another diagnosis.
• Red flags: haemoptysis, progressive dyspnoea, weight loss, night sweats.

• Occupational history of iron oxide exposure.
• Chest radiograph: diffuse, fine, dense, nodular opacities of 1 to 3 mm, symmetrical, mainly mid and lower zones, typically more radio opaque than silicosis nodules, with no hilar node enlargement.
• High resolution CT: poorly defined centrilobular nodules, ground glass density, minimal fibrosis.
• Spirometry and DLCO: normal in uncomplicated disease.
• Bronchoalveolar lavage with iron laden macrophages (Perls Prussian blue stain) and mineral analysis.
• Serum ferritin is normal; the process is local.
• Exclude silicosis, sarcoidosis, miliary tuberculosis, metastases, haemosiderosis (anaemia, haemoptysis, history of cardiac or autoimmune disease), and hereditary haemochromatosis.

• No drug treatment is required in uncomplicated disease. Counselling about exposure reduction is the core of management.
• Reduce exposure: wet drilling, dust suppression, ventilation, and P2 or P3 respirators.
• Stop smoking: varenicline 0.5 mg orally once daily for days 1 to 3, 0.5 mg twice daily for days 4 to 7, then 1 mg twice daily for 12 weeks; or nicotine patch 21 mg per 24 hours for 6 weeks, 14 mg for 2 weeks, then 7 mg for 2 weeks.
• Mixed dust disease with silica (siderosilicosis): radiograph and spirometry yearly, tuberculosis screening annually, HIV testing, and isoniazid 300 mg with pyridoxine 25 mg once daily for 6 months for latent infection when diagnosed.
• Follow up: chest radiograph every 3 years in uncomplicated cases; sooner if symptoms change.
• Radiographic regression usually occurs within 2 to 5 years of leaving exposure; failure to regress should prompt further investigation.
• Compensation and workplace notification.