Place of Siderosis in Pneumoconioses
Siderosis is a classic representative of metalloconioses, a broad group of occupational pneumoconioses resulting from long-term inhalation of industrial metallic dust. Alongside siderosis, the most studied conditions in this category include aluminosis and berylliosis. Other entities in clinical practice and pathology include titanosis, baritosis, stannosis, and several other dust-induced disorders.
Etiology and Occupational Risk Groups
The direct cause of siderosis is the systematic exposure of the respiratory tract to iron-containing dust. The condition has a clearly defined occupational nature, with heavy industry and metalworking workers forming the primary risk group.
Professions most susceptible to this disease include:
- Miners specializing in the extraction of hematite (red iron ore, chemical formula $Fe_2O_3$).
- Foundry workers regularly exposed to metallic aerosols.
- Specialists engaged in polishing various metal products.
- Nail manufacturing workers.
- Metal engravers.
- Electric arc welders.
Pathogenesis
Historically, the pathogenesis of siderosis was interpreted differently. Previously, the scientific community believed that iron dust itself was inert, and that pulmonary fibrosis was caused by an inevitable admixture of silicon dioxide. This condition was even designated as silicosiderosis.
Today, this theory has been revised. It has been reliably proven that iron-containing dust can independently initiate pulmonary fibrosis, without the involvement of silicon compounds.
A key feature of siderosis is its prolonged and predominantly benign course. The proliferation of connective tissue (fibrosis) is significantly less pronounced than in silicosis or silicatoses. The reason for this benign nature lies in the properties of the dust itself: iron particles lack direct tissue toxicity, are readily phagocytosed by macrophages, and are efficiently cleared from the body via the bronchial tree.
Macroscopic Appearance
During autopsy, lung morphology directly depends on the chemical composition of the inhaled dust. Traditionally, two main types of siderosis are distinguished:
- Red Siderosis. This form is caused by the prolonged inhalation of dust containing iron oxides. Macroscopically, the lungs are noticeably increased in volume, and the tissue acquires a distinctive yellowish-brownish-red color.
- Black Siderosis. This develops upon contact with dust containing iron protoxide, iron carbonates, or iron phosphates. In this case, the lungs turn a deep black color, visually resembling anthracosis (coal worker's pneumoconiosis).
Microscopic Appearance and Lymph Node Changes
Histological examination of the lung tissue reveals mild interstitial sclerosis. The parenchyma contains characteristic submiliary and miliary nodules, which are dense accumulations of macrophages ("dust cells") whose cytoplasm is densely packed with fine iron dust particles.
Few collagen fibers are identified among the clusters of dust cells. To confirm the presence of iron in tissues, a special histochemical stain is used—the Perls reaction, which is always positive in siderosis.
The pathological process affects not only the lungs but also the regional lymph nodes. They accumulate large amounts of dust delivered by macrophages, accompanied by significant diffuse sclerosis of the lymphoid tissue.