RESUMEN
Arthritis is an unusual manifestation of paraneoplastic syndrome, appearing in a variety of cancers, including pulmonary and colorectal. It can often pose a diagnostic challenge to physicians, since it may be difficult to distinguish from more commonly encountered rheumatic illnesses. Moreover, synchronous cancers are rare and unexpected in patients with symmetrical polyarthritis. Hypertrophic pulmonary osteoarthropathy is to be considered in patients with polyarthritis and lung neoplasia. The aim of this report is to highlight the case of a patient presenting with paraneoplastic polyarthritis, which led to identifying the presence of underlying synchronous lung and colorectal malignancies. Lymph node biopsy was performed raising suspicion of Caplan's syndrome but lung lobectomy confirmed adenocarcinoma. Rheumatologists should be reacquainted with rheumatic manifestations in malignant diseases.