Hypertrophic osteoarthropathy mimicking a reactive arthritis: a case report and review of the literature

Background: Hypertrophic osteoarthropathy (HOA) is a syndrome characterized by abnormal proliferation of skin and periosteal tissues of the extremities. It can be a rare hereditary disease (pachydermoperiostosis) or can be secondary to various diseases, though mostly lung malignancies. Here, we report an unusual clinical presentation of HOA. Case presentation: A 77-year-old man presented with fever, diarrhea, and an oligoarthritis involving the left knee and the ankles. Since left knee synovial fluid aspiration revealed an aseptic synovitis and Clostridium Difficile toxin was detectable in stool samples, a reactive arthritis secondary to a Clostridium Difficile induced colitis was initially suspected. However, the presence of a worsened digital clubbing and the lack of a good clinical response to steroid therapy led us to perform a radionuclide bone scanning, which revealed HOA. This turned out to be associated with a lepidic predominant lung adenocarcinoma, which was clinically and radiologically difficult to distinguish from a relapse of pneumonia. Conclusion: Consistent with the literature, HOA tends to have a variable clinical presentation, mimicking that of various rheumatic diseases. This clinical case shows that HOA can present as a presumptive acute reactive arthritis, and it highlights the importance of patient's follow-up in the differential diagnosis of inflammatory arthritis, especially when a worsened digital clubbing is present.