Abstract
Paraneoplastic rheumatologic syndromes encompass a range of clinical conditions that mimic primary rheumatic diseases and occur in the context of malignancy. Hypertrophic osteoarthropathy (HOA) is a notable example of such a syndrome, which is frequently associated with intrathoracic malignancies, including primary lung tumors and metastases. This report presents a case of a patient diagnosed with HOA secondary to lung adenocarcinoma, who was admitted with symmetric polyarthritis that resembled elderly-onset rheumatoid arthritis. Anti-cyclic citrullinated peptide (anti-CCP) antibodies are primarily associated with rheumatoid arthritis, but their levels can be falsely elevated in various other conditions. In clinical practice, it's essential to interpret anti-CCP antibody results in conjunction with other clinical findings and laboratory tests to arrive at an accurate diagnosis. This case underscores the importance of considering HOA in the differential diagnosis of inflammatory arthritis, particularly in patients with a known or suspected malignancy, especially in the presence of positive rheumatoid arthritis-specific antibodies. Also, recognition and treatment of the underlying condition can lead to substantial improvements in both rheumatologic and oncologic aspects.