Parâmetros de exposição à sílica e critérios clínicos na indicação da tomografia computadorizada de alta resolução de tórax em casos borderline de silicose

Abstract

Silicosis is an occupational pulmonary disease. It continues to be a serious public health problem, especially in developing countries, because of its high incidence and prevalence. The disease has a strong dose response gradient in relation to silica exposure. Hence, its veryimportant to know the dose of exposure in the clinical evaluation of the exposed people. Details of exposure, such as whether the worker has remained exposed to silica after disease diagnosis and total duration of silica presence in the lungs, can interfere on the presentation and prognoses of silicosis. The other factors that influence the occurrence of the disease include individual susceptibility, genetic and immunologic factors. Because there is no cure for the disease and it can pose a serious threat to workers quality of health and life, the early diagnosis followed by interruption of exposure, are regarded fundamental to secondary prevention to avoid disease progression to more severe forms. For this reason, the use of chest high resolution computed tomography (HRCT) has been increased as a diagnostic tool, especially in cases where the chest X-ray is dubious. However, until now, there is no clear agreement regarding the role of the HRCT on the earlydiagnoses of the disease. Moreover, there is a lack of studies on criteria to improve its indication when x-rays are dubious. Consequently, the cost/benefit relationship of HRCT on silica surveillance programs is unknown. The present study analysed a casuistic of 140 former gold miners, who were being investigated for silicosis by clinical and occupational history, chest X-ray and spirometry. Among them,those with normal or borderline chest X-ray were submitted to HRCT.In order to assess occupational exposure, we developed a cumulative silica exposure index based on full occupational history and pre-existing environmental evaluations. The continuity of exposure after silicosis diagnosis was associated with more severe forms ofthe disease in the subgroup of 83 confirmed cases of silicosis. We also found more severe forms of the disease among black workers, suggesting that they were exposed to more dusty conditions.We used the subgroup composed by the 69 workers considered normal or borderline by chest Xray, to build a flow chart to explore possible criteria to HRCT indication. We used several cut off point of the vital forced capacity (FVC) based on spirometry and the exposure index todifferentiate groups of cases and non cases of borderline silicosis in relation to their HRCT results. This way, we were able to identify the individuals that could mostly benefit of HRCT exam. In Brazil, the HRCT is considered a high cost exam, justifying the search for criteria to improveits indication among workers exposed to silica with dubious chest X-ray. In this way, the present study can represent an initial proposal.