Silicosis

M. Lingat, M.D., K.J. Malik, M.D., S. Raab, M.D., P.D. Kaplan, M.D.--Allegheny General Hospital, Pittsburgh, PA

Introduction: Silicosis is a fibrotic disease of the lung caused by pulmonary reaction to free crystalline silica. Radiographically it is manifested by small rounded opacities and occasionally by eggshell calcification of hilar nodes. It is predominantly a parenchymal disease. We report a case of endobronchial silicosis leading to broncholithiasis in the absence of other radiographic features typical of silica exposure.

Case Presentation: A 64-year-old retired coal miner was referred to the Pulmonary Clinic for evaluation of a 10 year history of recurrent pneumonias. He was a non smoker and had a benign past medical history. On physical exam, he was not dyspneic at rest. The breath sounds were normal with no adventitous sounds heard. Cardiac exam was normal. There was no clubbing, cyanosis, or peripheral edema. Chest roentogram demonstrated atelectasis. No rounded opacities were seen. CT scan revealed patchy infiltrates in both lower lung fields, associated with atelectasis. Spirometry was normal with an FVC of 4.78 (87%) and an [FEV.sub.l] of 3.81 (70%). The flow volume loop was normal. Flexible bronchoscopic examination revealed an exophytic endobronchial mass obstructing the right middle lobe bronchus. Biopsies of the lesion revealed fibrohistiocytic proliferation. On polatization, numerous small particles consistent with endobronchial silicotic nodules were found.

Discussion: The chronic fibrosing disease of the lungs caused by prolonged and extensive exposure to free silica has been recognized for centuries. Workers exposed to free silica may develop nodular lesions within the lungs that may coalesce into conglomerate or confluent lesions called massive fibrosis. This is defined as complicated silicosis, which may be associated with impaired lung function or even premature death. It is known that granulomatous infections such as Mycobacterium tuberculosis, Histoplasmosis and Coccidioidomycosis may cause broncholithiasis. Cahill, et al reported a case of broncholithiasis with silica exposure. Broncholiths can be deeply embedded into the wall of bronchus and erode into the lumen to cause symptoms such as cough, hemoptysis, lithotripsis, airway obstruction, pneumonia, and fistula formation. Radiographic manifestations include development of airway obstruction resulting in lobar or segmental atelectasis, mucosal impaction or air-trapping. Our patient had symptoms of cough and was treated for recurrent pneumonia twice in the year of diagnosis. Initially, his chest x-ray showed parenchymal densities without any nodules. A followup chest x-ray six months later showed atelectasis and consolidation of the right middle lobe. This was confirmed on CT scan. Bronchoscopy at the time showed an exophytic mass obstructing the right middle lobe. Upon biopsy, the histopathology was consistent with silicotic nodules reflecting his silica exposure. He developed endobronchial silicosis, which manifested as an exuberant growth of granulation tissue obstructing his airway causing atelectasis. Although Mycobacterial infection is often associated with patients, with silicosis, all his cultures were negative. Broncholithiasis may be ablated using YAG laser, and, at times, surgical resection may be necessary. Unfortunately, to-date, there is no specific treatment for silicosis. Current therapeutic measures include treatment of air flow obstruction or bronchodilators, treatment of respiratory tract infections with antibiotics, and the use of supplemental oxygen to prevent complications of chronic hypoxemia.

Conclusion: Endobronchial silicosis may present with radiographic features atypical of silicosis.

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