Caplan syndrome is a rare type of lung disease in which individuals suffering from rheumatoid arthritis develop lung nodules in association with exposure to silica and coal dust. Patient history, imaging studies, and serology are necessary steps in order to confirm this clinical entity.
Having in mind the frequent asymptomatic nature of coal worker's pneumoconiosis (CWP) or silicosis, the principal occupational factors in the pathogenesis of Caplan syndrome, patients often present with little or no respiratory symptoms  . Mild dyspnea, most notably on exertion, was noted as the principal complaint in recent case reports  , while a cough and hemoptysis are absent. In fact, the disease is often discovered incidentally, while virtually all patients present with one or more manifestations of rheumatoid arthritis (RA)  :
Although seen in a very small number of patients, cardiac (ischemic heart disease, cardiomyopathy, pericarditis) and hematologic (anemia, neutropenia, splenomegaly) features may also be encountered in RA patients .
Because Caplan syndrome is strongly associated with occupational exposure to coal dust or silica, a detailed patient history with an emphasis on previous occupations may be one of the most important steps during workup. Similarly, assessment of signs and symptoms suggestive of RA (if the diagnosis is not already known) can only be made after a meticulous history taking, but the role of a thorough physical examination is equally important. The diagnosis of Caplan syndrome, however, relies on findings obtained from imaging studies - radiography and computed tomography (CT) of the thorax  . Well-defined lung nodules that range from 0.5-5 cm, predominantly located in the periphery, are typical radiographic lesions seen in these patients  . Coalescence of nodules and formation of a large confluent nodule, cavitation or calcification may also be observed . On the other hand, confirmation of RA is necessary by performing appropriate laboratory tests, in addition to clinical criteria. Evaluation of C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies are mandatory if clinical suspicion toward RA exists. The combination of radiographic findings, occupational risk factors, and laboratory results should be sufficient to make the diagnosis of Caplan syndrome.