Caplans syndrome overview
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sharmi Biswas, M.B.B.S
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Overview
Caplan syndrome is known as Rheumatoid pneumoconiosis. This is a combination of Rheumatoid Arthritis and pneumoconiosis. It is a rare syndrome occurring mostly in miners exposed to silica, coal and asbestos. For the first time, Caplan, a British physician in 1953 first described this syndrome. It is hypothesized that silica get ingested by macrophages. Silica destroys the macrophages and again engulfed by another macrophage. This repeating process leads to chronic inflammation and fibrosis. Due to having the capability to move around, silica can travel to other organs away from lung and can induce autoantigens. Silica has an adjuvant effect on antibody production. In patients with silicosis , increased rheumatoid factor and antinuclear antibodies has been found. By producing TNF-α and Interleukin 1 , silica induces joint destruction. Silica also plays a role in inducing both innate and adaptive immunity. Patients with Caplan syndrome are mostly asymptomatic but in advanced stages dyspnea and cough might occur. In Caplan syndrome, increased inflammatory markers are found in serum study though there is no arthritis. Caplan syndrome with polyarthritis mostly positive for Anti citrullinated Peptide Antibodies (ACPA). Caplan nodules can appear with or before the onset of arthritis. In many cases miners have typical radiographic pictures of Caplan syndrome without any features of Rheumatoid Arthritis. Chest X ray findings of Caplan syndrome is characterized by well defined lung nodules of 0.5-5 cm throughout the lungs but predominantly in the peripheral areas. These nodules might appear as crops and later coalesce into a larger one. The onset of nodules are sudden, rapidly growing and can remain in the lungs for years longer. They might regress spontaneously unless get cavitated or calcified. Pleural effusion and pneumothorax are rare complications. CT scan findings are similar to chest x ray but provides more specific information such as mixed nodular infiltrative changes in lungs. But chest x ray or CT scan are not capable of differentiate between Caplan nodules and ordinary silicotic nodules. Biopsy is required to confirm the diagnosis. On histopathology, Caplan nodules show central necrosis similar to rheumatoid nodules except the presence of dust particles. Surrounding the dust ring there is a zone of inflammation consisting of granulocytes, macrophages and giant cells. This inflammatory zone is the distinguishable criteria of Caplan nodules from rheumatoid nodules. There is no definitive treatment for Caplan syndrome. Lung nodules in Caplan syndrome usually do not require any treatment until any complication develop. Disease modifying anti rheumatic drugs (DMARDs) can be used to treat Rheumatoid arthritis. But DMARDs have no role in treatment of pulmonary nodules. In some cases, corticosteroid found to be helpful to stop the progression of pulmonary nodules. Anti TNF therapy are commonly used in treatment of RA but recent study showed that Anti TNF therapy may induce pulmonary nodules. Anti TNF therapy play role in activating latent tuberculosis and silicosis increase the risk of tuberculosis infection . So, it is strongly recommended to screen for latent TB in the patients with Rheumatoid Pneumoconiosis. In irreversible pulmonary fibrosis lung transplant can be the ultimate choice.
Historical perspective
In 1953, the chest x ray findings of multiple pulmonary nodules, in the coal miners with Rheumatoid Arthritis(RA) of Welsh, was described by Caplan. In 1940 and 1955, rheumatoid nodules were described in autopsy study of heart and lungs. An epidemiological study was conducted by Miall and associates in 1955 to determine the validity of Caplan syndrome. J. Gough reported the histological diagnostic findings for Caplan Syndrome in 1958.
Pathophysiology
Caplan Syndrome is known as Rheumatoid pneumoconiosis. In patients with rheumatoid arthritis, lungs show increased immune response to the foreign materials. In coal miners with RA, exposure to silica causes the release of different cytokines as interleukin-1,granulocyte colony stimulating factor and tumor necrosis factor-alpha by monocytes and macrophages. Lymphocytes get activated by the cytokines and leading to hyperactive autoimmune response.