Migratory Polyarthralgias and Skin Rash: Rat Bite Fever with a Positive Anti–Cyclic Citrullinated Peptide

Rat bite fever is a rare, underdiagnosed disease caused by Streptobacillus moniliformis in the United States, and is typically characterized by leukocytosis, elevated C-reactive protein, migratory polyarthralgias, and pustular skin rash. Rat bite fever is frequently misdiagnosed as either a viral illness or a rheumatologic disease and carries a high mortality risk if untreated. We report the first case of rat bite fever associated with positive anti–cyclic citrullinated peptide. The patient initially presented with low back pain and developed a pustular rash as well as severe asymmetric polyarthralgias. Blood cultures turned positive for S. moniliformis and the patient completed a 4-week course of antibiotics for presumed septic arthritis.