Silicosis and Sarcoidosis: A Rare Association.

SESSION TITLE: Miscellaneous Global Case ReportsSESSION TYPE: Global Case ReportPRESENTED ON: Tuesday, October 28, 2014 at 01:30 PM - 02:30 PMINTRODUCTION: Silicosis is an occupational lung disease attributable to inhalation of silica dust.High-level exposure to respirable silica dust in the course of occupations such as quarrying,drilling,sandblasting and glass manufacturing can cause chronic inflammation and fibrosis in the lung.1 Sarcoidosis is a multisystem granulomatous disorder of unknown etiology with characteristic clinico-radiological findings and histopathological evidence of non-caseating granulomata.2 It occurs in genetically susceptible individuals through alterations in the immune response, following exposure to environmental, occupational or infectious agents2. Though individually not uncommon,the association of silicosis and sarcoidosis is rare.Weather the association is coincidental or both are triggered by a common factor, or there is a true-cause-effect relationship between the two conditions remains a controversy.Though the possibility of silica causing sarcoid in this case is more likely,due the effects of silica on the immune system.CASE PRESENTATION: A 45 year old man presented with a 3 year history of dry cough,breathlessness and wheeze. A smoker,worked in a metal-moulding company with significant silica dust exposure.Examination showed bilateral crackles and wheezes.Room air oxygen saturation was 95%.Chest radiography showed bilateral mid and lower zone reticulo-nodular shadows.Computed tomography of the chest revealed numerous, peri-bronchovascular nodular opacities.Lung function tests showed a restrictive pattern with a normal diffusion capacity.Serum angiotensin converting enzyme level was normal; Mantoux test was negative.Rheumatoid Factor and Anti-Nuclear Antibodies were negative.Open lung biopsy revealed numerous non-caseating granulomata composed of epitheloid cells and Langhans' type giant cells,some with asteroid bodies.Polarizing microscopy showed numerous refractile silica particles within nodules.The features suggested two co-existing pathological processes, silicosis and sarcoidosis. The patient was started on steroids,with symptomatic relief.

DISCUSSION: Silicosis results from high-level exposure to silica containing dusts. The basic pathology is fibrosis due to inflammation triggered by silica particles3. Silica can act as an adjuvant to enhance the immune response and trigger,promote or accelerate the development of the autoimmune diseases.3 Crystalline silica particles are extremely toxic to cells and cannot be broken down by lysozymal enzymes.Alveolar macrophages that ingest silica particles are damaged and get stimulated,resulting in inflammation and activation of fibroblasts3.The process repeats itself,resulting in spreading immune activity and fibrosis. Sarcoidosis sometimes co-exists with autoimmune diseases.Sarcoidosis involves oligoclonal T cell expansion driven by an antigenic stimulus.Granuloma formation in sarcoidosis requires an immunological trigger;silica being irritant may act as that trigger.In this case,histopathology showing the asteroid bodies together with the noncaseating granulomas and skin test for tuberculosis being negative,strongly suggested the diagnosis of sarcoidosis2.Though chronic exposure to low dose silica can cause granulomas,presence of inclusion bodies like the asteroid bodies in the silicotic granulomas is not a feature. The silicotic nodule,showing refractile particles is typical of silicosis.Hence these two different pathologies did co-exist in the same patient. While the literature linking silicosis and sarcoidosis is sparse,the association appears epidemiologically likely and biologically plausible.CONCLUSIONS: Silicosis and sarcoidosis can co-exist in the same patient and should be considered when the radiological features are not suggestive of a single pattern.The diagnosis must be confirmed by histopathology.While the mainstay of silicosis management is prevention of exposure,sarcoidosis is treatable.The impact of each disease on the other's progression,as well as the response to treatment is unclear and merits further study.Reference #1: Petsonk EL & Parker JE.Coal Workers' Lung Diseases and Silicosis.In AP Fishman & JA Elias editors. Fishman's Pulmonary Diseases and Disorders.New York: McGraw-Hill;2008.pp.974-976,1126,1129Reference #2: Leitch AG,Sarcoidosis.In A Seaton & D Seaton editors.Crofton and Douglas's Respiratory Diseases,5thed. : Wiley-Blackwell; 2000.pp.1035,1041-1042Reference #3: Parks CG, Conrad K,Cooper GS.Occupational exposure to crystalline silica and autoimmune disease.Environ Health Perspect.1999;107(Suppl 5):793-802DISCLOSURE: The following authors have nothing to disclose: Syed Tousheed, Tiyas Sen, Hemanth Kumar, Muralimohan BvNo Product/Research Disclosure Information.