Caplan syndrome presents with cough, shortness of breath, along with symptoms of rheumatoid arthritis such as prolonged morning stiffness, with symmetric arthritis in a systemic fashion. Physical examination typically shows rheumatoid arthritis findings for joints which are swollen, tender metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints, along with possible pulmonary findings such as rales, wheezes, and crackles. It is defined as lung nodules in work-exposed personnel, with nodules varying in size from 0.5 to 5 centimeters. The nodules may grow, remain unchanged, disappear, and then reappear.

The findings of this syndrome consist of rheumatoid nodules in the lungs noted as rounded opacities 0.5 to 5 centimeters which may cavitate and resemble tuberculosis on chest radiology. The opacities can differ in size, varying from small opacities which appear as simple pneumoconiosis and very large opacities which can appear as progressive massive fibrosis. There may be accompanying pleural effusion. Usually, the opacities coincide with the onset of arthritis, but there are reported cases where arthritis developed about 6 to 10 years before the lung lesions. Lung function tests may reveal a mixed restrictive and obstructive picture with a total loss of lung volume along with the reduced diffusing capacity of the lungs for carbon monoxide. Complete serum studies for rheumatoid factor; antinuclear antibodies may be present. Silicosis, asbestosis, and tuberculosis should always be in the differential.[6][7][8][9]

Caplan syndrome does not require treatment, and management should be focused on treating the extrapulmonary manifestations of rheumatoid arthritis. Previous studies involving treatment of lung lesions from this condition were disappointing as the assumption was made that the tubercle bacillus was a possible etiological factor in the causation of the lung lesions, and anti-tuberculous medications were given. In such cases, there is no obvious benefit. Once tuberculosis is excluded, treatment with steroids can be started. Exposure to the coal dust must be stopped along with other lung toxin exposures such as smoking. The RA should be treated per guidelines with disease-modifying antirheumatic drugs.

Asbestosis is a form of pneumoconiosis that presents in patients with chronic inhalation of a cumulative dose of inhaled asbestos fibers. The asbestos fibers are fibrogenic to the lungs, causing lung nodules that may appear similar to the radiologic imaging for Caplan syndrome. The difference is these patients have known exposure to asbestos inhalation such as with products containing asbestos cement-like pipes, shingles, clapboard, sheets, vinyl-asbestos floor tiles, asbestos paper in filtering and insulating products, brake linings, clutch facings, textile products such as yarn, felt tape, cord, rope, and spray products used for acoustic, thermal, and fireproofing purposes. Silicosis is similar to the pathogenesis of asbestos and is usually associated with workers in the sandblasting industry. 

Other Differentials for Multiple Cavitary Pulmonary Nodules

1. Neoplasm 
2. Infection with bacterial granulomatous such as fungi, mycobacterial, Nocardia, parasitic
3. Inflammatory such as granulomatosis with polyangiitis, Langerhans cell histiocytosis, sarcoidosis
4. Vascular such as pulmonary embolism with infarction
5. Developmental such as congenital pulmonary airway malformation, pulmonary sequestration
6. Drug toxicities with amiodarone, infliximab, bleomycin, carbamazepine
7. Amyloidosis

The prognosis of this condition depends on risk exposure and is similar to rheumatoid arthritis, except when the lung disease has progressed to an irreversible fibrosis stage. For the most part, the prognosis rarely causes disability due to lung problems because of standardized guidelines and treatments available to rheumatoid arthritis patients.

In some severe cases, the condition can progress to a more severe stage involving irreversible fibrosis stage. The patients typically will present with restrictive lung disease and symptoms of chronic shortness of breath and cough. More intensive treatment options should be considered in such severe cases along with transplant options.

Practitioners are advised to consult pulmonology for further assistance in patient care. 

People should avoid exposure to inorganic dust, risk factors such as sandblasting, or exposure to asbestos. 

Several case reports for Caplan syndrome, pulmonary function tests typically have shown mild airway obstruction. Constantinides et al. had a retrospective study and compared 24 patients with Caplan syndrome and 36 patients with progressive massive fibrosis, suggesting an overlap in pulmonary function tests. Caplan syndrome had less airflow obstruction compared to progressive massive fibrosis patients, without differences with respect to lung volumes and diffusion capacity. This study was adjusted for age, mining exposure, and smoking.

The diagnosis and management of caplan syndrome is best done with an interprofessional team that includes the primary care physician, nurse practitioner, pulmonologist, radiologist and pathologist. The majority of patients first come to attention at outpatient clinics where they may complain of dyspnea and/or joint pain. The diagnosis can be difficult but the condition does not require any specific treatment. The treatment is focused on treating the extrapulmonary manifestations of rheumatoid arthritis.

Exposure to the coal dust must be stopped along with other lung toxin exposures such as smoking. The RA should be treated per guidelines with disease-modifying antirheumatic drugs.

The prognosis for patients with Caplan syndrome is guarded; those with mild disease do not have reduced life expectancy, but those with severe disease may develop lung fibrosis which can be debilitating.[10] (Level V)