Enigmatic Cases of Finger Proximal Interphalangeal Joint Swelling: Case Series and Focused Review of the Literature.

Objectives: This case series and focused literature review address the diagnostic challenges and management strategies for patients presenting with atraumatic, isolated swelling, and stiffness of a single finger's proximal interphalangeal (PIP) joint. The dual emphasis is on synthesizing the lessons learned from our case series and providing a structured framework for clinical reasoning, including imaging, biopsy, and laboratory assessment. Non-traumatic causes of finger swelling may include rheumatological disease, atypical infection, tumor, or metabolic conditions. Routine evaluation includes history, examination, and radiographs. Additional evaluation may include ultrasound, inflammatory screening labs, magnetic resonance imaging (MRI) and computed tomography (CT). Despite these efforts, a diagnosis may still be elusive. The objective of this study is to provide a useful clinical differential diagnosis and provide lessons learned from this unique group of patients. Methods: Starting in February 2017, patients with isolated unilateral PIP swelling were followed. Clinical information was collected, including history, examination, and laboratory and imaging studies. Patients were followed until a specific diagnosis was obtained. In addition to the series of patients, a focused literature review is given to present additional unusual causes of atraumatic isolated PIP swelling that were not found in this series. Results: There were five cases that met the criteria. This includes two cases ultimately diagnosed with psoriatic arthritis, and one case each of osteoid osteoma, gout and palindromic rheumatoid arthritis. Conclusions: The single most effective test that helped to reach the final diagnosis in this series was the CT scan.