MRI, CT more sensitive than radiography for detecting bone erosions in patients with RA

Using CT as the reference, MRI showed moderate sensitivity and good specificity for detecting erosions; radiography showed low sensitivity.

Both magnetic resonance imaging and computed tomography are more sensitive than standard radiography for detecting bone erosions in patients who have rheumatoid arthritis of the wrist, according to a new study published in the journal Arthritis Research & Therapy.

Uffe Møller Døhn, MD, and colleagues at the Copenhagen University Hospital at Hvidovre, Denmark, evaluated the performance of MRI and radiography for detecting bone erosions, using multidetector CT as the reference. They also investigated whether measuring erosion volumes on CT and MRI is reproducible and correlated to semiquantitative erosion assessments on CT, MRI and radiography, according to the study.

Investigators performed all three imaging studies on one wrist joint of 17 rheumatoid arthritis (RA) patients and four healthy controls. All imaging studies were completed on the same day and scored separately according to the Outcome Measures in Rheumatology Rheumatoid Arthritis MRI Scoring System (for CT and MRI) or the Sharp/van der Heijde scoring method (radiographs).

Erosion volume measurements were performed twice, with a 1-week interval between assessments, according to the study.

Overall, researchers assessed 315 wrist bones for erosions. Of these, CT detected 166 erosions in 151 bones, MRI detected 119 erosions in 104 bones and radiography detected 43 erosions in 38 bones.

"With CT as the reference method, the overall sensitivity, specificity and accuracy (concordance) of MRI for detecting erosions were 61%, 93% and 77%, respectively, while the respective values were 24%, 99% and 63% for radiography," the authors reported. "Of the 119 MRI erosions, 92 (77%) could be confirmed with CT, whereas 36 (84%) of the 43 radiographic erosions were confirmed with CT."

When measuring erosion volumes, both CT and MRI showed high intramodality agreements, with a Spearman correlation coefficient of 0.92 for CT and 0.9 for MRI (P < .01).

For individual erosions, the correlation between volumes and scores was 0.96 for CT and 0.99 for MRI, and 0.83 for CT and 0.8 for MRI for subjects' total erosion volumes and total scores (P < .01), according to the study.

"With CT as the reference method, MRI showed moderate sensitivity and good specificity and accuracy for detection of erosions in rheumatoid arthritis and healthy wrist bones, while radiography showed very low sensitivity. The tested volumetric method was highly reproducible and correlated to scores of erosions," the authors wrote.

"The number of erosions detected on CT, as compared with MRI and radiography, indicate that CT is a very sensitive method for detecting bone erosions in RA wrist bones, and possibly even more sensitive than MRI. CT may therefore be of value for detecting and monitoring bone erosions in RA," they wrote.

"The sensitivity to change is not yet established, however, and CT is disfavored by using ionizing radiation and by the inability to visualize soft tissue changes," they noted.

"Owing to the high reproducibility, this quantitative method for assessing bone erosions in RA patients could be a useful tool in longitudinal studies, including randomized controlled trials, but further studies, including studies of sensitivity to change, are needed to clarify this issue," they wrote.

For more information:
Døhn UM, Ejbjerg BJ, Hasselquist M, et al. Detection of bone erosions in rheumatoid arthritis wrist joints with magnetic resonance imaging, computed tomography and radiography. Arthritis Res Ther. 2008;10:R25.