Age-related differences in collagen-induced arthritis: clinical and imaging correlations.

Arthritis is among the most common chronic diseases in both children and adults. Although intraarticular inflammation is the feature common among all patients with chronic arthritis there are, in addition to age at onset, clinical characteristics that further distinguish the disease in pediatric and adult populations. In this study, we aimed to demonstrate the utility of microCT (μCT) and ultrasonography in characterizing pathologic age-related differences in a collagen-induced arthritis (CIA) rat model. Juvenile (35 d old) and young adult (91 d old) male Wistar rats were immunized with bovine type II collagen and incomplete Freund adjuvant to induce polyarthritis. Naïve male Wistar rats served as controls. All paws were scored on a scale of 0 (normal paw) to 4 (disuse of paw). Rats were euthanized at 14 d after the onset of arthritis and the hindpaws imaged by μCT and ultrasonography. Young adult rats had more severe signs of arthritis than did their juvenile counterparts. Imaging demonstrated that young adult CIA rats exhibited more widespread and severe skeletal lesions of the phalanges, metatarsals, and tarsal bones, whereas juvenile CIA rats had more localized and less proliferative and osteolytic damage that was confined predominantly to the phalanges and metatarsals. This report demonstrates the utility of imaging modalities to compare juvenile and young adult rats with CIA and provides evidence that disease characteristics and progression differ between the 2 age groups. Our observations indicate that the CIA model could help discern age-related pathologic processes in inflammatory joint diseases.