Osteoporosis is a common and serious complication of the autoimmune disorder systemic lupus erythematosus (SLE). Women with SLE are at a higher risk for reduced bone mineral density (BMD) and have a high prevalence of osteoporosis and osteoporotic fractures. However, not enough is known about osteoporosis prevalence and risk factors in Chinese patients with lupus nephritis (LN), a severe manifestation of SLE.
To address this knowledge gap, Dr. Yu Hong and colleagues conducted a single-center, cross-sectional study of patients with renal biopsy-proven LN at Tongji Hospital in Wuhan, China, from May 2011 to June 2018. The patients’ BMD was measured using dual x-ray absorptiometry at the lumbar spine, total hip, and femoral neck. Findings of the study appeared in BMC Nephrology.
Information collected included age at enrollment, ethnicity, menstrual status, age at menopause, personal history of fractures, alcohol consumption, and smoking status. Laboratory investigations, such as measurements of serum creatinine, uric acid, urea nitrogen, and serum ionized calcium, were also collected, and weight, height, and body mass index (BMI) were measured.
In addition, information about disease duration, calcium supplements, anti-osteoporotic therapy, and corticosteroid use were noted, along with the maximum and current dosages. The Systemic Lupus Erythematosus Disease Activity Index was used to score disease activity. Disease damage was evaluated based on criteria established by the Systemic Lupus International Collaborative Clinics/American College of Rheumatology.
There were 130 participants enrolled in the study, of whom 128 (98.5%) were female and two were male. Mean age (±SD) was 46.2±12.9. Of the female participants, 61 were premenopausal and 67 were postmenopausal. Postmenopausal participants were older, had been diagnosed with LN at a later age, and had higher weight, lower height, higher BMI, higher blood urea nitrogen level, and more frequent bisphosphonate use than the premenopausal participants (P<.05).
To compare values between the premenopausal and postmenopausal groups, the researchers used statistical tests, including two-tailed t test, Mann-Whitney U test, Fisher’s exact test, χ2 test with Yates correction, and χ2 test, based on the distribution of the data and the type of variables. They used univariate logistic regression analysis to identify factors that might be associated with osteoporosis. Variables that showed statistical significance in the univariate analysis, plus age, were then incorporated into a multivariate logistic regression model to determine the independent predictors of osteoporosis.
When compared with premenopausal participants, those who were postmenopausal had significantly reduced BMD in the lumbar spine (L1-L4) (0.802±0.165 vs 0.877±0.151 g/ cm2, P=.008) and total hip (0.760±0.143 vs 0.814±0.125 g/cm2, P=.027). Postmenopausal patients also had lower T scores at the lumbar spine (L1-L4) (–2.194±1.434 vs –1.372±1.403, P=.002), femoral neck (–1.576±1.240 vs –1.160±1.052, P=.047), and total hip (–1.491±1.167 vs –1.079±1.037, P=.041). In addition, postmenopausal participants demonstrated a significantly higher prevalence of osteoporosis at the spine (L1-L4) (50.7% vs 19.7%, P<.001), femoral neck (29.9% vs 4.9%, P<.001), total hip (25.4% vs 6.6%, P=.009), and at least one measured site (55.2% vs 24.6%, P<.001).
Age at menopause, weight, height, and BMI might positively correlate with BMD in the lumbar spine, total hip, and/or femoral neck. Meanwhile, age, age at diagnosis of LN, and menopause duration might negatively correlate with BMD in the same regions. Multivariable linear regression analysis showed that BMI was positively associated with BMD. Disease duration and menopause duration were negatively associated with BMD of the lumbar spine, total hip, and femoral neck.
Univariate logistic regression analysis for osteoporosis showed that older age, older age at diagnosis of LN, younger age at menopause, lower weight, shorter height, and absence of bisphosphonates were potential risk factors among patients with LN. In premenopausal participants, shorter height was a potential risk factor for osteoporosis. Among postmenopausal participants, younger age at menopause, lower weight, shorter height, lower BMI, and absence of bisphosphonates might be risk factors for osteoporosis.
Multivariate logistic regression analysis showed that older age, lower weight, and absence of bisphosphonates were independently associated with an increased risk of osteoporosis among participants with LN. Shorter height was independently associated with an increased risk of osteoporosis among premenopausal participants. Younger age at menopause, lower weight, and absence of bisphosphonates were independently associated with an increased risk of osteoporosis among postmenopausal participants.
The authors acknowledge certain limitations of their study. By including patients with LN at various disease durations for BMD measurements, potential variability of results may have been introduced. Differences in treatments that patients received may have introduced confounding factors that could influence the association between risk factors and osteoporosis. Some factors that could be associated with osteoporosis, such as serum vitamin D levels, were not assessed and adjusted. Lastly, participants were diagnosed by means of renal biopsy, and most had good renal function, which may not be representative of all patients with LN.
In summary, the authors wrote, “Our findings indicate that patients with LN are at significant risk of developing osteoporosis, particularly in the lumbar spine and among postmenopausal individuals. The risk factors associated with osteoporosis that were identified may include older age, lower weight, and the absence of bisphosphonate treatment.”
Source: BMC Nephrology
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