Progressive massive fibrosis (PMF) of silicosis is the most severe form of complicated silicosis (silicosis with PMF). It represents progression from simple nodular silicosis (small rounded opacities <1 cm) to large conglomerate fibrotic masses, typically >1 cm and often >10 cm, located bilaterally in the upper lung zones with cephalic retraction. PMF can develop in any worker chronically exposed to crystalline silica (quartz, cristobalite, tridymite), particularly in mining, quarrying, foundry work, sandblasting, granite/stone cutting, ceramic and glass manufacturing, and—most recently—artificial/engineered stone fabrication where high silica content (>90%) and intense exposure cause rapid disease.
Pathophysiology involves inhalation of respirable crystalline silica particles (1-5 μm) deposited in distal airways and alveoli, ingestion by alveolar macrophages with cytotoxic cell death, release of inflammatory cytokines (IL-1β via NLRP3 inflammasome, TNF-α, TGF-β), activation of fibroblasts, deposition of collagen, and formation of silicotic nodules with characteristic onion-skin lamellar pattern. Progression to PMF occurs through nodule coalescence and ongoing fibrogenic stimulation, even years after exposure ends. Recent epidemics in artificial stone (engineered quartz countertops) workers worldwide have shown accelerated and severe disease in young workers, often within 5-10 years of exposure.
Clinical course includes progressive exertional dyspnea, productive cough, fatigue, weight loss, and—as disease advances—hypoxemia, respiratory failure, and cor pulmonale. Imaging features include large conglomerate masses (often with central necrosis or cavitation in TB superinfection), upper lobe distortion with cephalic hilar retraction, eggshell calcified hilar/mediastinal lymphadenopathy. Complications include silico-tuberculosis (5-30x increased TB risk), lung cancer (silica is IARC Group 1 carcinogen), autoimmune diseases (systemic sclerosis, RA, SLE, ANCA vasculitis—Erasmus syndrome), pneumothorax (cavitating PMF), and chronic respiratory failure. Treatment: removal from further exposure, smoking cessation, supplemental oxygen, pulmonary rehabilitation, treatment of complications (anti-TB, anti-cancer), screening for autoimmune disease, and lung transplantation in selected end-stage cases. No proven antifibrotic therapy for PMF, though investigational agents are being studied. Prevention through enforced dust control, wet methods, ventilation, and respiratory protection is essential.