Among patients with rheumatoid arthritis (RA), there is a correlation between the cortical thickness relative to the transverse diameter of third metacarpal bone and bone mineral density (BMD), suggesting this can be a promising screening tool for osteoporosis in this population, according to study results published in Bone.

Patients with RA are at increased risk for osteoporosis and fragility fractures. While dual-energy X-ray absorptiometry (DXA) is the gold standard for the diagnosis of osteoporosis, it is not widely available in many countries worldwide. Here the researchers sought to determine whether a screening index for BMD loss can be used as a substitute to the DXA method.

The Sharp/van der Heijde Scores were calculated using X-ray pictures of both sides of the hand. All patients with RA treated at Yoshii Hospital, Kochi, Japan, between April 2014 and September 2019, were subjected to the routine administration of X-ray pictures of the bilateral hands and feet at the first consultation and thereafter in order to calculate Sharp/van der Heijde Scores. Cortical thickness and the transverse diameter of the mid-portion of the metacarpal bone of the right middle finger were calculated and researchers determined the Cortical Thickness Ratio (CTR) as the cortical diameter relative to the transverse diameter. At the same time, BMD of the lumbar spine and femoral neck was measured.


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Using the receiver operation characteristics (ROC) technique, the cut-off index of the CTR to the BMD was calculated. In addition, sensitivity, specificity, area under the curve, and the odds ratio for T-score < -2.5 were evaluated.

 The cross-sectional study included 300 patients with RA (87.4% women, mean age 73.9 years). The mean transverse width of the third metacarpal bone was 7.3 mm and the thickness of the cortex was 2.0 mm, thus the average ± SD CTR was 0.279±0.124.

There was a significant correlation between CTR and BMD in both the lumbar spine and femoral neck according to DXA testing.

In ROC analysis, the cut-off index of the CTR was 0.25 for the lumbar spine and femoral neck. For the lumbar spine, the sensitivity was 67.9% and the specificity was 83.0%, with an area under the curve of 0.78, and an odds ratio of 4.17 (95% CI, 2.51-6.92). For the femoral neck, sensitivity was 76.1%, specificity was 81.6%, the area under the curve was 0.81 with an odds ratio of 4.90 (95% CI, 2.75-8.73).

The index was examined in treatment naïve patients in order to eliminate confounding of drug interventions, and the data suggested the CTR is a potential useful tool for the initial screening of osteoporosis for patients who are naïve for osteoporosis and RA treatment.

“[T]he CTR may be a strong candidate marker for screening for osteoporosis in patients with RA with the index less than 0.25. These findings may provide physicians with the diagnosis of osteoporosis in patients with RA,” concluded the researchers.

Reference

Yoshii I, Akita K. Cortical thickness relative to the transverse diameter of third metacarpal bone reflects bone mineral density in patients with rheumatoid arthritis. Bone. 2020;137:115405. doi:10.1016/j.bone.2020.115405