Hypertrophic Osteoarthropathy: A Case of an Undifferentiated Polyarthritis.

Hypertrophic osteoarthropathy is a paraneoplastic syndrome and is considered an important secondary cause of rheumatic disease. It typically manifests as tibial and femoral bone pain, with arthralgia or synovitis of adjacent joints also being common findings. Usually, musculoskeletal symptoms accompany the course of the disease, disappearing with treatment of the neoplasm and recurring coincidentally with the tumor relapse. The authors report a case of a patient with hypertrophic osteoarthropathy, whose etiological study allowed the diagnosis of a lung adenocarcinoma, particularly challenging due to the patient's young age and the absence of associated symptoms.