Osteoporosis may develop in three distinct patterns as periarticular, marginal erosions and widespread in patients with RA. Generalized bone loss is an early feature of RA and its prevalence is estimated approximately two fold higher than the healthy population
11, 16. This early bone loss is more pronounced in hands than in hip and lumbar spine
17-19.
Periarticular bone loss has been demonstrated in certain body areas using different methods 21-22. Hand joints are the target joints in RA and assessment using radiographic or other imaging techniques gives detailed information about disease status and outcome. It is clear that hand BMD measurement using DEXA is a precise, repeatable and reliable method. The hand BMD has been shown to correlate with BMD at other parts of the body 23. Different radiographic scoring methods have been developed to evaluate the disease progression in RA however they had restricted ability to evaluate bone mineralization 23.
Many studies 18, 20, 24-26 have been published about the assessment of BMD in hand and forearm of RA patients. However to our knowledge, there is no study assessing periarticular and/or total foot BMD in RA using the DEXA method. Foot joints are weight bearing joints and also target for inflammation in RA. BMD measurements of calcaneus by DEXA have been considered to have low long-term consistency 27. However, it was noted that heel DEXA can be used to scan OP in risk groups 28.
Peel et al. 20 reported that the hand BMD was lower with respect to other areas in the postmenopausal patients with RA. Devlin et al. 24 showed correlation between CRP levels, an activity marker, and hand BMD. In our study, there was a negative correlation between right and left foot BMD and ESR.
Shibuya et al. 21 reported that BMD measurements on mid radius and calcaneus were significantly lower in postmenopausal patients with RA than patients with osteoarthritis except BMD at lumbar spine. These authors also showed close correlation between BMD in all areas and severity markers for the disease and body mass.
Shenstone et al. 29 reported correlation between BMD and HAQ score, and also showed relationship between lumbar BMD and baseline Stoke Index. The BMD loss was found to be higher in femur neck in early stages of the RA regardless of disease activity and functional loss. But, in our study, there was no relation between BMD with Stoke Index.
We found that FFI was positively related to disease duration, ESR, VAS pain, morning stiffness, RAI and HAQ. The femur trochanter BMD and FFI were negatively correlated. It is considered that hip BMD is more related to disability, pain and functional limitation in patients with RA in accordance with above mentioned studies.
Ozgocmen et al. 30 compared HAQ and Larsen scores with BMD measurements from axial, total hand and 2.metacarpal middle shaft in 30 RA patients and 29 healthy females, no correlation was found between HAQ and other parameters. They reported that Larsen score had slightly negative correlation with BMD of second.metacarpal middle shaft and the total hand BMD had positive correlation with lomber spine and femur neck BMD. In accordance with the previous studies, we found a negative correlation between foot BMD and SJSN and SES but not with Larsen score.
Plain radiographs are routine methods to evaluate joint damage and disease progression in RA. They are beneficial in pursuing natural continuity of disease and detecting treatment. Radiographic evaluation has many advantages. It reflects time of joint pathology and allows repeated evaluations. Also it has advantages like repeatability, highly assessed validity and sensitivity to change 10. Many scoring methods only include hand radiographs; but it was reported that erosions may develop earlier on the foot region of patients with RA 31. Paimela et al. 31 suggested that radiographic modifications of feet are more sensitive than modifications of hand in early RA and for this reason radiographic evaluations should be included in the RA classification criteria. Particularly, diagnostic sensitivity increases when hand and foot radiographs were evaluated together in early disease 2, 26, 31-36. Foot joints are frequently involved in RA and results in functional limitations. Bone loss in the feet results from combined effects of localized and generalized inflammation. We also consider other concomitant effects like menopausal status and glucocorticoid use. It was noted in most publications that in order to increase sensitivity of radiological criteria, feet should be analyzed along with hands 33. In addition to this, radiological modifications occur in time 34, 35.
In our previously published study 10, we measured hand, spine and femur BMD by DEXA in patients with RA and healthy controls. We found a moderate relationship between radiographic scores and hand BMD with Larsen, Sharp/van der Heijde and SENS (simple erosion narrowing score). While the hand BMD was found to be lower in the RA patients, there was no difference between the axial BMD. As the hand BMD correlated significantly with disease duration and CRP levels, we suggested that radiographic scores were beneficial in estimating hand BMD 10.
Our results reveal that foot BMD measurement using DEXA is a practical, repeatable and easy method. Foot BMD measurement may reflect both localized and generalized bone loss and may be a potential outcome measure particularly in patients with marked foot involvement.
Conflict of Interest
No conflict of interest is declared by the authors.
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