Abstract Introduction Caplan syndrome, also known as rheumatoid pneumoconiosis (RP), is defined by pulmonary nodules in patients with rheumatoid arthritis (RA) and inorganic dust exposure, classically coal or silica. U.S. prevalence is 1% among coal workers, while other non-coal exposures, such as marble, remain underdescribed. We report a granite, quartz and marble worker whose imaging mimicked miliary tuberculosis (TB). Case Presentation A 38-year-old man with RA and severe hand arthritis refractory to multiple biologic therapies presented with chronic dry cough. He had household exposure to active TB and over 10 years of occupational exposure to granite, quartz and marble dust through countertop fabrication and installation. Chest CT showed innumerable bilateral miliary-type nodules. Bronchoalveolar lavage (BAL) cytology was negative for malignancy; however, a positive AFB stain from sputum culture, despite three negative MTB PCRs, prompted empiric RIPE therapy for presumed miliary TB. He received two months of therapy without improvement. Repeat BAL and peribronchial biopsies revealed pigmented macrophages with amorphous and occasional-birefringent crystalline material. CT-guided biopsy of a new subpleural cavitary lesion showed necrotizing granulomatous inflammation with palisading histiocytes and surrounding fibrosis. The presence of dust-laden macrophages containing amorphous, refractile, and few birefringent crystals supported a mixed-dust (atypical) Caplan nodule. After discontinuing anti-TB therapy and resuming biologic treatment for RA, pulmonary and joint symptoms improved, with radiographic stabilization. Discussion While granite and quartz (both silica-containing) exposure is a recognized cause of RP, this case highlights a mixed-dust pattern with marble contribution (predominantly calcium carbonate). In macrophages, marble dust appears as finely granular, yellow-brown to gray cytoplasmic inclusions that are amorphous or refractile on light microscopy and typically non-polarizable or only faintly-birefringent on polarized light. Anthracotic/hemosiderin admixture, common in smokers, may yield iron-positive pigment and obscure optical properties. These deposits can provoke mild fibrohistiocytic reactions forming irregular fibrotic nodules rather than classic silicotic ones. In our patient, weak birefringence and absence of silicotic nodules favored mixed-particle exposure over pure silicosis. Diagnostic delay resulted from prior TB exposure, immunosuppression, and central sampling instead of peripheral biopsy, where Caplan nodules predominate. Detailed occupational history, serial imaging, and clinicopathologic correlation are essential to distinguish RP from infection or neoplasia. Conclusion RP should be considered in RA patients with diffuse nodules and any inorganic dust exposure, even beyond traditionally recognized dusts. Mixed-particle exposure may obscure characteristic histology and delay recognition. Awareness of these variants enables recognition and targeted management of the underlying condition. This abstract is funded by: None
Pozo et al. (Fri,) studied this question.
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