Osteoporosis Risk Factors and Bone Mineral Density in Women With MS

Suzanne C. Smeltzer, RN, EdD, FAAN; Vanessa Zimmerman, RN, MSN; Theresa Capriotti, RN, MSN, DO; and Lilia Fernandes, BSN, MSN
Suzanne C. Smeltzer is an Associate Professor and Project Director with the Health Promotion for Women with Disabilities Project, Villanova University College of Nursing, Villanova, Pennsylvania. Vanessa Zimmerman is an Administrative Research Associate with the Health Promotion for Women with Disabilities Project, Villanova University College of Nursing. Theresa Capriotti is an Assistant Clinical Professor at Villanova University College of Nursing. Lilia Fernandes is a former graduate assistant at Villanova University College of Nursing.

Abstract

Purpose: To describe the results of bone mineral density (BMD) screening in women with multiple sclerosis (MS) and to identify risk factors for osteoporosis in women with MS and their use of preventive strategies.

Methods: BMD screening was performed at the os calcis. A self-administered survey, formatted as a checklist, asked women with MS about their risk factors for osteoporosis and their use of osteoporosis prevention strategies.

Findings: 142 women with MS completed the study. Using a modified classification system suggested for use with peripheral measurements of BMD, 44.4% of women in the sample were categorized as having normal BMD, 35.2% were osteopenic, and 20.4% were osteoporotic. The number of risk factors for osteoporosis reported by women with MS ranged from zero to 10 with a mean of 4.6 ± 1.8. Relatively few women were using strategies to minimize their risks for osteoporosis. Of those who did employ a risk-minimization strategy, the lowest number of women in the sample (4.3%) used raloxifene, and the highest number of women (38.6%) used calcium supplementation.

Conclusions: Low BMD is common in women with MS, increasing their risk for osteoporosis and osteoporotic fractures. Greater awareness is needed among health care providers regarding the increased risk and high incidence of osteoporosis in women with MS. Strategies to detect and prevent osteoporosis are warranted in women with MS in order to prevent further disability caused by osteoporosis-related fractures.

Suggested citation: Osteoporosis Risk Factors and Bone Mineral Density in Women With MS. Smeltzer, SC, et al. Int J MS Care [Serial on-line]. March 2002;4(1).

Osteoporosis is a skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture.¹ It has been referred to as a “silent” disease that is a major contributor to morbidity and mortality in the United States and around the world.^2,3 Osteoporosis is considered epidemic among women in the general population and is a major risk factor for fracture.¹ The costs of treating fractures secondary to osteoporosis are estimated to exceed $15 billion per year⁴; these costs are expected to rise exponentially and to triple by 2040.³

Osteoporosis contributes to 90% of hip fractures in women. Most hip fractures result from falls, which is an issue of heightened concern for patients who are at increased risk for falling, such as those with MS. Osteoporotic fractures have the potential for causing chronic pain, disability, and loss of function and independence. All patients who sustain hip fractures because of osteoporosis require hospitalization for treatment, and two thirds of them fail to return to their baseline level of functioning. Nearly one third of patients with osteoporosis-related hip fractures are discharged to nursing homes within a year; one in five patients die in the year following fracture.^1,4

Osteoporosis and osteoporosis-related fractures are likely to increase disability in women already disabled by the primary progressive neuronal degeneration of MS. Few studies have investigated the risk and incidence of osteoporosis in women with preexisting disability. As a result, little is known about the risk and incidence of osteoporosis in women with preexisting disabilities such as MS.

Inadequate physical activity, lack of weight bearing, sedentary lifestyle, and chronic use of steroids are known risk factors for osteoporosis. These factors are common among women affected by MS. Because of impaired balance, lack of coordination, and lower extremity weakness, falls in women with MS are more likely and increase the risk for fractures in the presence of low bone mineral density (BMD) and osteoporosis. Several investigators have found increased incidence of fractures in persons with MS.^5-7 Subjects in these studies have largely been patients with significant disability because of MS or patients who have been undergoing treatment with steroids for exacerbations or progression of MS. Risk factors associated with fractures in these studies have included low BMD, steroid use, and inadequate dietary intake of vitamin D. Incidence of osteoporosis in persons with MS has not been well described. Additionally, the relationship of osteoporosis to fracture in persons with MS has not been investigated.

The purposes of this study were to: 1) describe the results of BMD screening in women with MS, 2) identify risk factors for osteoporosis in women with MS, 3) describe their use of osteoporosis prevention strategies, and 4) examine the frequency of previous BMD testing in these women and their compliance with recommendations for testing.

Methods

The methods used in this study included BMD screening and a self-report questionnaire. The study was approved by the appropriate institutional review board prior to recruitment of subjects.

BMD screening was performed at the os calcis. A peripheral instantaneous x-ray imager (PIXI), manufactured by Lunar Corporation, was used to measure peripheral BMD. Measurements were obtained by a technician skilled with this method of screening. PIXI employs dual-energy x-ray absorptiometry (DEXA), considered the current gold standard and the most accurate method of measuring BMD presently available.⁴

BMD is reported as a T-score, which represents the patient’s bone mineral content in grams per square centimeter compared with the mean of a population of young adults. An individual’s T-score refers to the number of standard deviations (SD) above or below the mean BMD for young, healthy white women.^2,4

Validity of Peripheral DEXA as a Measure of BMD

Decreased BMD has been identified as the strongest predictor of osteoporosis-related fractures.^8-10 While DEXA measurements of the hip are the most sensitive predictors of hip fractures, BMD measurements obtained at the os calcis have also shown excellent predictability for assessing risk for hip fractures.¹¹

Sensitivity and specificity of peripheral DEXA at the os calcis for identifying osteoporosis and osteopenia when compared with measurements made at the femur have been reported to be 94% and 69%, respectively.¹² The os calcis has been reported to be the optimal single site to use for screening for potential fractures¹³; however, there are several limitations of peripheral DEXA at the os calcis. First, it provides measurement at a single site and does not directly assess risk for fractures of the hip and spine,⁴ and second, the method may not be sensitive in all situations. Thus, there may be false-negative results suggesting normal BMD when in fact the person has low BMD.¹¹

Despite these limitations, peripheral BMD screening can provide information about the need for more definitive diagnostic testing. Although there is less experience with measurement of peripheral bone sites such as the os calcis as a predictor of hip fracture, such measurements have been shown to be equivalent to more central sites, such as the hip and the spine.¹¹ The small size of the PIXI apparatus, its lack of movable parts, and its speed of operation make it ideal for BMD screening.¹² It is a portable and less expensive method of assessing BMD as compared with methods that assess hip and spine BMD. Thus, peripheral BMD measurement by PIXI is appropriate for BMD screening outside of imaging centers and is more accessible for screening of physically disabled persons who are confined to wheelchairs or have gait disturbances.

Self-Report Survey

A self-administered survey was formatted as a checklist requiring minimal effort to complete. It included questions about risk factors for osteoporosis, use of osteoporosis prevention strategies, previous BMD screening or testing, and recommendations for such testing by subjects’ health care providers. The risk factors listed were those widely recognized as associated with osteoporosis; they included age, sex, race, menopausal status, family history of osteoporosis, use of medications, use of caffeine and alcohol, inadequate calcium intake, history of smoking, thin frame, and lack of weight-bearing activity.^3,4 Other demographic data, including ambulatory status, educational level, and employment status, were also obtained by questionnaire.

Data Analysis

Descriptive statistics were used to report means; SDs; ranges of BMD T-scores; frequencies of BMD T-scores that were categorized as normal, osteopenic, and osteoporotic; osteoporosis risk factors; and preventive strategies used by women with MS. Unpaired t-tests were used to compare mean T-scores by nominal variables (menopausal status, history of BMD testing, previous recommendation for BMD testing) where appropriate.

Sample

To be eligible for the study, women had to report a diagnosis of MS, have no possibility of pregnancy, be willing and able to undergo BMD screening, and attend one of four health fairs for persons with MS, since these were the sites where bone density screening was provided without cost to the participants. Women also had to be able to understand the questions in the survey and give written informed consent. Consecutive subjects who approached the screening site at the health fair and met the eligibility criteria participated in the study; data were obtained from each subject one time only.

The sample included 142 women with a self-reported diagnosis of MS. The sample was largely composed of middle-aged women with a mean age of 49.3 years (SD = 9.6), with a range of 27 to 74 years. Nearly 90% of the sample members identified themselves as white. Approximately three fourths of the subjects reported having attained an educational level beyond high school. Almost half of the women in the sample reported that they were unable to work; 33.8% of them indicated that they received disability benefits.

Women reported their ambulatory status as fully ambulatory, ambulatory with problems or requiring assistance, or wheelchair bound. More than 82% of the sample members reported that they were able to ambulate, although more than half of this group reported that they had difficulty walking. Sixty-five percent of the ambulatory subjects reported use of some assistive device (ie, canes or crutches), and 38.1% of those who described themselves as able to walk reported use of a wheelchair part of the time. Approximately 17% of the sample reported that they required a wheelchair at all times. The demographic characteristics of the sample are summarized in Table 1.

Results

Results of BMD testing are reported as T-scores, which reflect the number of SDs of subjects’ values from the population mean of young, healthy white women.⁴ The World Health Organization (WHO) defines normal BMD as a T-score greater than –1.0, osteopenia as a T-score between –1.0 and –2.5, and osteoporosis as a T-score of –2.5 or less. Severe osteoporosis is defined as more than 2.5 SD below the mean with fragility fractures.²

The mean T-score of the sample of 142 women was –.69 ± 1.5; T-scores ranged from a high of 2.9 to a low of –4.6. Using the WHO criteria for normal BMD, osteopenia, and osteoporosis, 56.3% of the subjects had T-scores indicating normal BMD, 33.1% had osteopenia, and 10.6% were categorized as osteoporotic. Thus, 43.7% of the sample had BMD values indicating either osteopenia or osteoporosis.

Alternate Method of Reporting BMD Results

Because of concern that the WHO categorization may not be sensitive enough when applied to peripheral measurement of BMD and therefore may yield false-negative results, another classification scheme has been suggested.¹⁴ In this modified classification system, normal BMD is indicated by a T-score greater than 0.6; osteopenia, by a score between –0.6 and –1.6; and osteoporosis, by a score lower than –1.6. When this modified classification system was used, 44.4% of the women in the sample were categorized as having normal BMD, 35.2% demonstrated osteopenia, and 20.4% had frank osteoporosis. Thus, 55.6% of the women had T-scores indicative of osteopenia or osteoporosis. These results are summarized in Table 2.

Self-Reported Osteoporosis Risk Factors Among Women With MS

The number of risk factors reported by the sample ranged from zero to 10 with a mean of 4.6 ± 1.8. Table 3 identifies the percentage of women reporting the presence of each risk factor. Menopausal status contributed to the osteoporosis risk of women in this sample. Unpaired t-tests demonstrated that there were significant differences (t = 2.4, df = 140, P = .02) in the mean BMD T-score of the 62 women in the menopausal group (M = –1.04, SD = 1.6) and the mean BMD T-score of the 80 women in the premenopausal or the perimenopausal group (–.42, SD = 1.4). By WHO criteria, 54.8% of menopausal women and 35% of premenopausal or perimenopausal women were identified as having low BMD. By the alternate classification scheme, 66.1% of menopausal and 47.5% of premenopausal or perimenopausal women had low BMD values.

Use of Osteoporosis Prevention Strategies by Women With MS

Table 4 summarizes the subjects’ reported use of strategies considered useful for reducing the risk for low BMD and osteoporosis. The percentages of women reporting use of each of the preventive strategies range from a low of 4.3% (for raloxifene use) to a high of 38.6% (for calcium supplementation). Less than one quarter of the sample used hormone replacement therapy (HRT) or participated in weight-bearing exercise. Less than one tenth of the sample took raloxifene or alendronate, a bisphosphonate used to prevent or treat osteoporosis.

Self-Reported Previous BMD Screening or Testing

When asked if they had undergone previous BMD testing or screening, 23.2% of the sample (n = 33) reported that they had. The percentage of women who reported having had testing recommended to them by a health care provider was 31.2% (n = 44). Twenty-seven (61.4%) of those who had received such recommendations had undergone BMD testing prior to participating in this study. Significantly, 68.8% (n = 97) reported that BMD testing had never been recommended by a health care provider. Of those 109 women who had not undergone previous testing, 37.6% had T-scores equal to or less than –1.0, and 9.2% had T-scores of less than –2.5, indicating osteopenia and osteoporosis, respectively.

Discussion

The findings of this study demonstrate that low BMD is common in women with MS; this was true whether the WHO criteria or the modified criteria was used to categorize subjects’ T-scores. While the mean T-score of –.69 would be indicative of normal BMD by WHO standards, according to the modified classification system, this score would be indicative of osteopenia. Diagnosis of osteopenia is important because it identifies women at risk for osteoporosis and fractures if bone loss continues.¹⁵

While 44.4% of the sample in this study had normal BMD values using the modified classification system, T-scores as low as –4.9 were obtained. Each SD decrease in BMD is thought to represent a 12% decrease in bone¹⁵; the risk for fractures increases approximately 1.5 to three times for every decrease of 1 SD in BMD below the mean.¹⁰ A reduction of the T-score to –2.0 has been used to define fracture threshold, the value below which non-traumatic fractures begin to occur.³ Therefore, a T-score of –4.9 indicates very severe osteoporosis even in the absence of non-traumatic fractures and represents almost a tenfold increase in risk for fractures. In a recent two-year study in which persons with MS and age- and sex-matched healthy control subjects were compared, MS patients were found to have significantly more non-traumatic fractures than were subjects in the control group.⁷ Fractures occurred in 2% of control subjects and in 22% of MS patients over two years (P < 0.002).

Risk for fractures is of particular concern because of the increased risk for falls in patients with MS, because of impaired coordination, ataxia, balance problems, and muscle weakness associated with the disease. The cognitive impairment that occurs in some persons with MS has also been suggested as a cause of falls.⁵ Therefore, women with MS and low bone density have an increased susceptibility to falls and to bone fractures.

While others have reported a high prevalence of low bone density or a high rate of fracture in persons with MS,^5-7,16 previous research has largely targeted persons with more advanced MS rather than the type of women included in this study. Lack of regular physical activity has been identified as a factor in bone loss and the progression of osteoporosis.^3,4,17,18 While inability to ambulate has been identified as a risk factor in general and in persons with MS,¹⁶ in this study, ambulatory status alone was not a predictor of decreased bone mass. In the present study, 17.3% of the subjects reported requiring a wheelchair at all times. Although 82.7% were ambulatory with or without assistive devices, only 18.7% of women reported participating in any weight-bearing exercise. Their lack of participation in exercise despite physical status that would permit some exercise may be due in part to fear of falling, to fatigue, or to lack of awareness that exercise or activity is needed to reduce the risk for osteoporosis. While the need for assuring safety during exercise is essential, given the risk for falls and fractures, the need for women with MS to participate in exercise within their physical limitations needs to be addressed.

Other osteoporosis risk factors that have been identified for women with MS include corticosteroid use, white race, inadequate calcium and vitamin D intake, the absence of exposure to sunlight, and accelerated bone loss.^7,16,19,20 Menopause without use of HRT increases the risks further, as is demonstrated by lower T-scores and higher incidence of osteopenia and osteoporosis in study participants who are menopausal.

Because of recent emphasis on the use of medications (eg, alendronate, raloxifene, estrogen, calcium supplements) to prevent and reverse bone loss, osteoporosis is no longer a disease that is inevitable and untreatable.^3,4,21 The National Osteoporosis Foundation and National Institutes of Health Consensus Conference have recommended that treatment be initiated when the patient’s T-score is lower than –2.0 if no other risk factors are present and less than –1.5 if the patient has other risk factors.^3,4 Although therapy is now available to treat low bone mass,²² few women in this study reported use of medications or other strategies to prevent or slow the loss of bone mass. Because not all women are eligible, able, or willing to take medications with demonstrated effectiveness in treatment or prevention of osteoporosis, other prevention strategies are of interest. Not all women in the sample, notably those who are premenopausal, are candidates for medications such as HRT; nevertheless, few of them use other prevention or treatment strategies such as calcium supplementation.

The findings of this study strongly suggest that additional strategies to prevent osteoporosis or reduce its severity are warranted in women with MS. This includes educating women who have MS about the importance of adequate calcium intake, weight-bearing exercise within their physical limitations, consideration of appropriate medications, and avoidance of smoking, caffeine, and alcohol. Although only 29.5% of women in the sample reported consumption of a diet low in calcium, it is likely that the incidence of low calcium intake is far greater than reported, since the calcium intake of most people in this country is far below the recommended amount.¹

Although the decreased bone mineral screening values reported in this study are a measure of peripheral BMD rather than a measurement of BMD of the hip and spine, the values do suggest the need for diagnostic testing using DEXA or quantitative computerized tomography. Such testing of these more crucial central sites is needed to determine if treatment is warranted. Despite the high incidence of low BMD and the presence of a number of osteoporosis risk factors in this sample, few women (23.2%) reported having undergone BMD screening or testing prior to this study, and only 31.2% reported having received a recommendation for testing from their health care provider. While one might argue that there is inadequate justification for BMD testing, the mean number of osteoporosis risk factors identified by the women in this sample (4.6 ± 1.8) and the number of women with low BMD upon screening suggest that risk factors were not assessed or recognized in these women by their health care providers or by the women themselves. More women with low BMD reported that they had undergone previous BMD testing or had had it recommended than did those with normal BMD. However, of the 79 who had T-scores indicative of low bone mass, 64.6% reported no previous BMD testing and 58.2% had received no recommendations for testing. While the value of universal screening, especially in premenopausal women, has not been established, the findings of this study suggest that there is adequate justification for considering screening in women who have MS with several osteoporosis risk factors.

Thirty-one percent of the sample members reported that they had received recommendations from their health care providers for BMD testing; however, 38.6% of these women had failed to comply with the recommendations. Clearly, recommending testing once without following up is inadequate to convince many women to undergo testing or to persuade them of its importance. Their failure to follow through with recommendations for testing may be due in part to lack of understanding of the significance of their osteoporosis risks and to limited access for testing. Following up recommendations for testing is needed, given the concomitant health problems and barriers to access encountered by women with MS and other disabilities that may keep them from complying with these recommendations. It is more likely than not that follow-up on recommendations by their health care providers will increase women’s understanding of the importance of testing. Access to screening and reimbursement for BMD testing may be an issue for some women with MS because of their disability and should be addressed with them.

Many women in this study were unaware of their risks for osteoporosis or their low BMD and, consequently, few were implementing strategies to reduce their risks for osteoporosis. Though one potential limitation of this study rests in the fact that it employed only self-reported data, its findings are consistent with the results of other studies.²³ A recent report revealed that only 7% of women with osteoporosis were aware of their condition.²⁴ If women with MS and their health care providers were aware of the women’s BMD value and their osteoporosis risk profile, there is a greater likelihood that strategies to prevent and treat osteoporosis would be implemented.

While there has been a growing recognition of the importance of prevention, detection, and treatment of osteoporosis in otherwise healthy men and women, the matter has greater urgency for women with MS. However, Shabas and Weinreb report that osteoporosis in women with MS is rarely if ever addressed by their health care providers.²³ Fifty percent of the 200 women with MS who participated in their study of the adequacy of preventive health care services reported that they did not have regular medical checkups; they reported seeing a primary care or family health care provider only when a problem occurred. Yet, in their visits with neurologists, women with MS reported that their MS-related issues—such as progression of MS and disability, treatment of MS, and management of MS-related signs and symptoms—often take precedence; as a result, little attention is given to health promotion issues, including risk for osteoporosis.²³ As a consequence, the risk for osteoporosis in MS is often not addressed. Because many women with MS have a normal or near-normal life span, it is incumbent on health care providers to assist them in prevention of osteoporosis and osteoporotic fractures that may lead to secondary disabilities. The findings of this study strongly suggest the need for considerably greater attention to osteoporosis risk and BMD testing in women with MS. The consequences of secondary disabilities related to fracture, in addition to preexisting disability as a result of MS, mandate further attention to these issues.

Summary

For women with MS, the need to prevent additional disability caused by low BMD is a high priority. Because of the increased risk for fractures and the potentially devastating consequences of fractures in patients with MS, greater attention should be given to reducing risks for osteoporosis in women with MS, particularly in those with impaired balance, impaired coordination, and lower-extremity weakness. The women who participated in this study were active enough to attend a health fair. Thus, their BMD values are likely to be higher than those of women with more severe disability due to MS who are less active and unable to participate in such events.

Health care providers need to become more aware of the increased risk of osteoporosis in women with MS, and they need to implement proactive strategies, including pharmacologic treatment, to prevent osteoporosis in this population. BMD testing is critical in women with MS, regardless of their menopausal status, because of their increased risk for low bone mass. Osteoporosis-related fractures would increase the severity of disability in women with MS. Interventions to prevent bone loss and osteoporosis-related fracture in women with MS are needed. Currently, there is a lack of adequate BMD testing of women with MS. BMD testing followed by treatment, if warranted, is a simple health promotion strategy to prevent further disability in women with MS. Health care providers of women with MS need to be aware of these clients’ increased risk of osteoporosis and their critical need for BMD testing.

Acknowledgments/Funding

This study was carried out as part of the Health Promotion for Women with Disabilities Project at Villanova University College of Nursing, and was funded by the Bristol-Myers Squibb Foundation. The authors also thank John Demas of UltraMed Imaging Services, Inc. for his assistance with this study and his commitment to women with disabilities.

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