Recurrently Infected Rheumatoid Nodule Causing Posterior Interosseous Nerve Palsy: A Report of a Rare Case.

Rheumatoid nodules are typically benign and asymptomatic, requiring no specific treatment. However, we encountered a diagnostically challenging case involving a painful elbow mass that rapidly enlarged. The lesion eventually caused posterior interosseous nerve (PIN) palsy. Surgical excision revealed histological features of a rheumatoid nodule with marked neutrophilic infiltration, raising suspicion of superimposed infection. Despite initial negative cultures, the lesion recurred aggressively, and infection was later confirmed by pathogen isolation. After adjusting immunosuppressive therapy and administering antibiotics, the patient achieved long-term remission with functional recovery. This case underscores the importance of distinguishing infection from rheumatoid activity in atypical nodular presentations.