- Email: [email protected]
Comparison of Ultrasound Measurements at the Heel Between Adults With Mental Retardation and Control Subjects
Bone Vol. 22, No. 6 June 1998:665– 668
Comparison of Ultrasound Measurements at the Heel Between Adults With Mental Retardation and Control Subjects T. J. ASPRAY,1 R. M. FRANCIS,1 A. THOMPSON,2 S. J. QUILLIAM,3 D. J. RAWLINGS,2 and S. P. TYRER4 1
Musculoskeletal Unit, Freeman Hospital, Newcastle upon Tyne, UK Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, UK 3 Castle Surgery, Prudhoe, Northumberland, UK 4 Prudhoe Hospital, Prudhoe, Northumberland, UK 2
Introduction Little is known about the prevalence of metabolic bone disease among adults with mental retardation (now known as learning disability), although they may be at increased risk of fractures. Broadband-ultrasound attenuation (BUA) and velocity-of-sound (VOS) measurements were performed on the left heel of 170 patients in a large hospital for adults with mental retardation. For 108 of these patients, age- and gender-matched control subjects were recruited from the local community, who also underwent BUA and VOS measurements. The mean age of matched pairs of patients and control subjects was 54 (range 32– 83) years for men and 53 (range 27– 82) years for women. Mean 6 SEM BUA for male patients was 52 6 4 dB/MHz and 89 6 2 for control subjects, whereas for female patients it was 34 6 3 dB/MHz and 68 6 2 for control subjects. VOS was 1603 6 7 m/sec for male patients and 1649 6 5 for control subjects, and 1573 6 7 m/sec for female patients and 1623 6 5 for control subjects. All differences between patients and control subjects were significant (p < 0.005). Dual-energy X-ray absorptiometry bone mineral density (BMD) measurements were also performed in seven patients with BUA less than 50 dB/MHz, four of whom were found to have a lumbar spine or femoral neck BMD more than 2.5 SD below the mean value for young adults. This study shows that patients with mental retardation have a marked reduction in BUA and VOS measurements at the heel, compared with age-matched control subjects. There is a need to identify the major causes of low bone mass in this group, as there may be potentially avoidable risk factors for osteoporosis, such as vitamin D deficiency and hypogonadism. (Bone 22:665– 668; 1998) © 1998 by Elsevier Science Inc. All rights reserved.
Little is known about the prevalence of metabolic bone disease among adults with mental retardation, now known as learning disability. However, there is some evidence to suggest a higher risk of fracture than in the community as a whole.12 Most people with mental retardation live in the community, but the hospitals that were built to supply residential care for these individuals still provide a service for a sizeable minority. Northgate and Prudhoe Hospital NHS Trust is the largest residential institution in the United Kingdom that looks after adults with mental retardation. Although the introduction of Community Care policies has led to the discharge of many residents,4 over 200 people still live in the hospital. In this group of patients with mental retardation and associated behavior problems, measurements of bone mass have not been attempted previously. Most techniques such as dual-energy X-ray absorptiometry (DXA) or quantitative computed tomography (qCT) are impractical, requiring transport of the individual to another hospital and accurate positioning of the subject, both of which prove difficult in this population. Alternative techniques are available, such as ultrasound measurements of the heel, which have been shown to correlate with risk of fracture, particularly at the hip.5,14,17 Ultrasound equipment is portable and measurements require a brief scan time with no exposure to ionizing radiation. Subjects and Methods All 205 patients living in Prudhoe Hospital were considered for the study. Broadband ultrasound attenuation (BUA) and velocity of sound (VOS) were measured at the left heel in 92 males and 78 females (82.9% of total population). Ultrasound measurements were not performed in five patients because of inability to obtain consent from the next of kin. Anatomical deformity at the heel prevented a satisfactory scan in 15 patients and behavioral problems precluded measurements in a further 15 cases. Ultrasound measurements were also performed in 50 male and 58 female control subjects, who were matched with hospital patients for age and gender. The control subjects were randomly selected and recruited from an age/gender register of a local general medical practice. Control subjects taking hormone re-
Key Words: Bone mineral density; Broadband ultrasound attenuation; Mental retardation; Osteoporosis; Ultrasound; Velocity of sound.
Address for correspondence and reprints: Dr. R. M. Francis, Musculoskeletal Unit, Freeman Hospital, Newcastle upon Tyne NE7 7DN, UK. E-mail: [email protected] © 1998 by Elsevier Science Inc. All rights reserved.
665
8756-3282/98/$19.00 PII S8756-3282(98)00054-4
666
T. J. Aspray et al. Heel ultrasound in adults with mental retardation
Bone Vol. 22, No. 6 June 1998:665– 668
Table 1. Mean 6 SEM BUA and VOS measurements in 108 patients with mental retardation and age- and gender-matched control subjectsa Both genders Patients BUA (dB MHz21) Mean [range] difference BUA z score VOS (m/sec) Mean [range] difference VOS z score
Controls
42 6 3
78 6 2 36 [233–125] 22.1 6 0.1 20.1 6 0.1 1587 6 5 1635 6 4 48 [2131–196] 0.24 6 0.07 0.73 6 0.05
Males Patients 52 6 4
Females Controls
89 6 2 38 [233–125] 22.1 6 0.2 0.0 6 0.1 1603 6 7 1649 6 5 46 [274–176] 0.58 6 0.07 1.06 6 0.05
Patients
Controls
34 6 3 68 6 2 34 [223–91] 22.2 6 0.2 20.2 6 0.1 1573 6 7 1623 6 5 50 [2131–196] 20.06 6 0.09 0.49 6 0.06
Differences between patients and control subjects are all statistically significant (p , 0.005).
a
placement therapy or other medications for osteoporosis prevention or treatment were excluded. BUA and VOS were measured at the left calcaneus using an ultrasound machine, the CubaClinical Mark 2 (McCue Ultrasonics, Winchester, UK). In seven patients with low BUA (all less than 50 dB/MHz), who were able to travel to another hospital and who were not behaviorally disturbed, DXA bone mineral density (BMD) measurements of the lumbar spine and femoral neck were performed using a Hologic-2000 QDR. The ultrasound machine was calibrated against the manufacturer’s phantom in the factory with no significant change in BUA or VOS during the study. The coefficient of variation (CV) for phantom measurements using the machine was 0.47% for BUA and 0.11% for VOS. CV for in vivo measurements on a single subject during the study was 2% for BUA and 0.3% for VOS. Ethical approval for the study was obtained from the Northumberland Ethical Committee. Written consent was obtained from control subjects, and consent was acquired from Prudhoe Hospital residents, their relatives, or a hospital advocate as appropriate. Results are presented for all patients with mental retardation and for the 108 matched pairs of patients and control subjects as summary statistics. In addition to the individual measurements of BUA and VOS, results are also expressed in standard deviation units from the mean for young men and women (t scores) and from the mean for age-matched individuals (z scores). The normative data for the CubaClinical Mark 2 were obtained from Sheffield, UK (unpublished data). Paired t-tests were performed on the difference between ultrasound measurements in residents and controls (DATA DESK, version 4.1, Ithaca, NY).
female patients and 28 of 50 male patients had BUA measurements at least 2 SD units below the expected mean value for the patient’s age (Figures 2 and 3). Of the seven patients with mental retardation and low BUA (less than 50 dB/MHz) who also underwent DXA bone density measurements, four had a lumbar spine or femoral neck BMD more than 2.5 SD units below the mean value for young adults of the same gender (Table 2). Discussion Our study clearly shows that hospital residents with mental retardation have a marked reduction in BUA and VOS measurements at the heel, compared with age-matched control subjects. Bone ultrasound measurements are thought to reflect both bone density and architecture.7 Heel ultrasound measurements correlate relatively poorly with DXA measurements at other sites, but the correlation with BMD at the calcaneus is good.15 Ultrasound measurements at the heel also predict mechanical properties of the calcaneus in vitro.10 Furthermore, prospective studies show that ultrasound measurements predict future hip fracture risk,5,14 independent of BMD.17 The low BUA and VOS values in the hospital patients with mental retardation therefore suggest that these individuals may be at increased risk of fracture. This is supported by low DXA measurements at the spine and hip in the small group of relatively compliant patients investigated with this technique. Studies of osteoporosis in patients with mental retardation are
Results The mean age of the patients with mental retardation living at Prudhoe Hospital was 54 years (range 27– 87), whereas that for the matched pairs of patients and control subjects was 54 years (32– 83) for men and 53 years (27– 82) for women. In the total group of 92 male hospital patients, mean 6 SEM BUA was 51 6 3 dB/MHz and VOS was 1603 6 5 m/sec. In 78 female hospital patients, BUA was 34 6 3 dB/MHz and VOS was 1574 6 6 m/sec. BUA and VOS measurements on the total group of 170 patients with mental retardation were not significantly different from the 108 patients who were matched with community controls (Table 1). The control subjects had mean BUA values similar to the normal ranges provided by the manufacturers, such that the mean z score in both males and females was close to zero (Table 1). The mean VOS was higher in the control subjects than expected from the normal ranges provided by the manufacturers, but the reason for this is unclear (Table 1). Both BUA and VOS measurements were significantly lower (p , 0.005) in patients of both genders with mental retardation than in control subjects (Table 1 and Figure 1). Thirty-two of 58
Figure 1. BUA measurements at the left heel in 108 patients with mental retardation and age- and gender-matched control subjects.
Bone Vol. 22, No. 6 June 1998:665– 668
T. J. Aspray et al. Heel ultrasound in adults with mental retardation
667
Figure 2. Cumulative frequency of BUA z score for females with mental retardation and control subjects.
few, although fractures have been reported to be more common in adults with the condition.12,13 Children with cerebral palsy and mental retardation have recently been shown to have low BUA at the heel and reduced spine BMD, as measured by qCT.18 Reduction in bone density has previously been reported in a number of psychiatric conditions, including depression, schizophrenia, and anorexia nervosa.11,16 The pathogenesis of osteoporosis in these conditions is varied, but may include estrogen deficiency and hypercortisolism.11,16 There are a number of other reasons why patients with mental retardation may be at risk of developing osteoporosis and fractures. Excessive trauma due to epileptic fits may be associated with increased fracture incidence.1,12 Vitamin D deficiency may predispose to both osteomalacia and osteoporosis and is prevalent among institutionalized communities.3 Drugs that affect vitamin D status, especially anticonvulsants,6 are commonly prescribed in patients with mental retardation. Physical inactivity may be associated with osteoporosis. Hypogonadism in men and women causes osteoporosis and may be more common in this population.8 We plan to evaluate these risk factors in the group of residents studied in due course. There were technical difficulties with ultrasound measurements in patients with mental retardation because of behavioral
problems and anatomical deformities at the foot. However, the magnitude of the difference in BUA and VOS between patients and controls is highly significant and unlikely to be explained by technique alone. Institutional lifestyle in the patients with mental retardation may explain some of the difference in ultrasound measurements, as the control group by definition included mainly active individuals. It is also possible that differences in nutrition and body size may contribute to differences in BUA and VOS. Previous large studies in elderly or institutionalized individuals have not demonstrated the low or negative BUA measurements seen in the present study.5,14 The earlier studies were performed using a water bath system, whereas we chose a system using ultrasound gel for acoustic coupling, as we felt this would be more acceptable in our group of potentially disturbed patients. Nevertheless, diffraction may theoretically occur around the edges of the ultrasound transducers, particularly if there is anatomical deformity of the calcaneus or movement of the foot. We also discussed our findings with one of the investigators who developed the technique of bone ultrasound measurement. He suggested that the negative values represented a low bone mass at the limits of detection for the machine, possibly compounded
Figure 3. Cumulative frequency of BUA z score for males with mental retardation and control subjects.
668
T. J. Aspray et al. Heel ultrasound in adults with mental retardation
Bone Vol. 22, No. 6 June 1998:665– 668
Table 2. DXA bone density measurements of the lumbar spine and femoral neck in seven patients with mental retardation who had low BUA results
Gender
Age
Mobile
BUA (dB/MHz)
t score (z score)
BMD spine (g/cm2)
t score (z score)
BMD femur (g/cm2)
t score (z score)
Female Female Female Male Male Male Male
43 50 74 41 45 45 55
No No Yes Yes Yes Yes Yes
5 21 210 210 47 49 47
25.2 (24.2) 25.5 (24.2) 26.1 (23.6) 26.8 (25.7) 23.9 (22.6) 23.5 (22.4) 23.7 (22.5)
1.016 0.945 0.724 0.999 0.699 0.856 0.488
20.28 (0.08) 20.31 (0.43) 22.93 (20.57) 20.84 (20.70) 23.56 (23.33) 22.14 (21.91) 25.48 (24.99)
0.778 0.776 0.571 0.554 NDa 0.592 0.547
21.24 (20.64) 21.19 (20.15) 23.23 (20.68) 22.32 (21.17) NDa 23.51 (22.53) 23.93 (22.57)
a
Not done.
by problems with diffraction associated with foot deformity (Dr. C. Langton, Hull University, personal communication). Impaired mobility associated with low BMD localized to the heel has also been previously suggested as a possible cause for particularly low BUA at the calcaneus.12 Our data on DXA scans in subjects with low BUA may support this finding. Although four of the seven patients had low BMD at the spine or femoral neck (t score , 22.5), the two women who were immobile had disproportionately low BUA and may have low bone mass confined to the calcaneus. The BUA measurements for control subjects were similar to the Sheffield reference database, effectively excluding operator-dependent problems as the explanation for the abnormally low values in patients with mental retardation. Although the VOS measurements in our control subjects were higher than the manufacturer’s normative data, they are comparable with recently published normal ranges for adults in the UK.9 Furthermore, patients with mental retardation had significantly lower VOS measurements than age-matched control subjects recruited from the local community. There is a need to identify the causes for low bone mass in this group of individuals with mental retardation. Some potential risk factors for reduced bone density and fracture may be avoidable or treatable, such as vitamin D deficiency and hypogonadism, in both genders. Hormone replacement therapy is not always considered in hypogonadal women with mental retardation, and testosterone treatment may be withheld in hypogonadal men because of concerns about behavioral problems.2 As the population ages and more people with mental retardation live in the community, fractures are likely to pose a significant problem, so strategies aimed at fracture prevention will need to be developed.
Acknowledgments: The authors thank Dr. T. P. Berney and Dr. M. S. Bhate for allowing us to study their patients and also for helpful advice, and J. Borland and all the staff of Prudhoe Hospital for their help in the study. Reverend M. Wheelwright acted as hospital advocate. We are grateful to the staff of Castle Surgery and all those who agreed to take part in the study. The study was supported by Eli Lilly Pharmaceuticals, the National Osteoporosis Society, the British Geriatrics Society, and Procter and Gamble Pharmaceuticals.
2. Aspray, T. J., Francis, R. M., Rutter, M., and Walker, M. Consequences of withholding testosterone treatment. Lancet 348:609; 1996. 3. Chapuy, M. C., Arlot, M. E., Duboeuf, F., Brun, J., Crouzet, B., Arnaud, S., Delmas, P. D., and Meunier, P. J. Vitamin D3 and calcium to prevent hip fractures in elderly women. N Engl J Med 327:1637–1642; 1992. 4. DHSS. Better Services for the Mentally Handicapped (Cmnd. 4683). London: HMSO; 1971. 5. Hans, D., Dargent-Molina, P., and Schott, A. M. Ultrasonographic heel measurements to predict hip fractures in elderly women: The EPIDOS prospective study. Lancet 348:511–514; 1996. 6. Harrington, M. G. and Hodkinson, H. M. Anticonvulsant drugs and bone disease in the elderly. J R Soc Med 80:425– 427; 1987. 7. Heaney, R. P. and Kanis, J. A. The interpretation and utility of ultrasound measurements of bone. Bone 18:491– 492; 1996. 8. Huovinen, K. J. Gynecological problems of mentally retarded women. A case-control study from southern Finland. Acta Obstet Gynecol Scand 72:475– 480; 1993. 9. Langton, C. M. and Langton, D. K. Male and female normative data for ultrasound measurement of the calcaneus within the UK adult population. Br J Radiol 70:580 –585; 1997. 10. Langton, C. M., Njeh, C. F., Hodgkinson, R., and Currey, J. D. Prediction of mechanical properties of the human calcaneus by broadband ultrasound attenuation. Bone 18:495–503; 1996. 11. Michelson, D., Stratakis, C., Hill, L., Reynolds, J., Galliven, E., Chrousos, G., and Gold, P. Bone mineral density in women with depression. N Engl J Med 335:1176 –1181; 1996. 12. Nakken, K. O. and Lossius, R. Seizure related injuries in multihandicapped patients with therapy-resistant epilepsy. Epilepsia 34:836 – 840; 1993. 13. Nilsson, O. S., Lindholm, T. S., Elmstead, E., Lindba¨ck, A., and Lindholm, T. C. Fracture incidence and bone disease in epileptics receiving long-term anticonvulsant drug treatment. Arch Orthopaed Trauma Surg 105:146 –149; 1986. 14. Porter, R. W., Miller, C. G., Grainger, D., and Palmer, S. B. Prediction of hip fracture in elderly women: A prospective study. Br Med J 301:638 – 641; 1990. 15. Ross, P., Huang, C., Davis, J., Imose, K., Yates, J., Vogel, J., and Wasnich R. Predicting vertebral deformity using bone densitometry at various skeletal sites and calcaneus ultrasound. Bone 16:325–332; 1995. 16. Salisbury, J. J. and Mitchell, J. E. Bone mineral density and anorexia nervosa in women. Am J Psychiatry 148:768 –774; 1991. 17. Turner, C. H. and Peacock, M. Calcaneal ultrasound measurements discriminate hip-fracture independently of bone mass. Osteopor Int 5:130 –135; 1995. 18. Wilmhurst, S., Ward, K., Adams, J. E., Langton, C. M., and Mughal, M. Z. Mobility status and bone density in cerebral palsy. Arch Dis Child 75:164 –165; 1996.
References 1. Annegers, J. F., Melton, L. J., III, Sun, C. A., and Hauser, W. A. Risk of age-related fractures in patients with unprovoked seizures. Epilepsia 30:348–355; 1989.
Date Received: July 9, 1997 Date Revised: January 21, 1998 Date Accepted: January 21, 1998
Comparison of Ultrasound Measurements at the Heel Between Adults With Mental Retardation and Control Subjects T. J. ASPRAY,1 R. M. FRANCIS,1 A. THOMPSON,2 S. J. QUILLIAM,3 D. J. RAWLINGS,2 and S. P. TYRER4 1
Musculoskeletal Unit, Freeman Hospital, Newcastle upon Tyne, UK Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, UK 3 Castle Surgery, Prudhoe, Northumberland, UK 4 Prudhoe Hospital, Prudhoe, Northumberland, UK 2
Introduction Little is known about the prevalence of metabolic bone disease among adults with mental retardation (now known as learning disability), although they may be at increased risk of fractures. Broadband-ultrasound attenuation (BUA) and velocity-of-sound (VOS) measurements were performed on the left heel of 170 patients in a large hospital for adults with mental retardation. For 108 of these patients, age- and gender-matched control subjects were recruited from the local community, who also underwent BUA and VOS measurements. The mean age of matched pairs of patients and control subjects was 54 (range 32– 83) years for men and 53 (range 27– 82) years for women. Mean 6 SEM BUA for male patients was 52 6 4 dB/MHz and 89 6 2 for control subjects, whereas for female patients it was 34 6 3 dB/MHz and 68 6 2 for control subjects. VOS was 1603 6 7 m/sec for male patients and 1649 6 5 for control subjects, and 1573 6 7 m/sec for female patients and 1623 6 5 for control subjects. All differences between patients and control subjects were significant (p < 0.005). Dual-energy X-ray absorptiometry bone mineral density (BMD) measurements were also performed in seven patients with BUA less than 50 dB/MHz, four of whom were found to have a lumbar spine or femoral neck BMD more than 2.5 SD below the mean value for young adults. This study shows that patients with mental retardation have a marked reduction in BUA and VOS measurements at the heel, compared with age-matched control subjects. There is a need to identify the major causes of low bone mass in this group, as there may be potentially avoidable risk factors for osteoporosis, such as vitamin D deficiency and hypogonadism. (Bone 22:665– 668; 1998) © 1998 by Elsevier Science Inc. All rights reserved.
Little is known about the prevalence of metabolic bone disease among adults with mental retardation, now known as learning disability. However, there is some evidence to suggest a higher risk of fracture than in the community as a whole.12 Most people with mental retardation live in the community, but the hospitals that were built to supply residential care for these individuals still provide a service for a sizeable minority. Northgate and Prudhoe Hospital NHS Trust is the largest residential institution in the United Kingdom that looks after adults with mental retardation. Although the introduction of Community Care policies has led to the discharge of many residents,4 over 200 people still live in the hospital. In this group of patients with mental retardation and associated behavior problems, measurements of bone mass have not been attempted previously. Most techniques such as dual-energy X-ray absorptiometry (DXA) or quantitative computed tomography (qCT) are impractical, requiring transport of the individual to another hospital and accurate positioning of the subject, both of which prove difficult in this population. Alternative techniques are available, such as ultrasound measurements of the heel, which have been shown to correlate with risk of fracture, particularly at the hip.5,14,17 Ultrasound equipment is portable and measurements require a brief scan time with no exposure to ionizing radiation. Subjects and Methods All 205 patients living in Prudhoe Hospital were considered for the study. Broadband ultrasound attenuation (BUA) and velocity of sound (VOS) were measured at the left heel in 92 males and 78 females (82.9% of total population). Ultrasound measurements were not performed in five patients because of inability to obtain consent from the next of kin. Anatomical deformity at the heel prevented a satisfactory scan in 15 patients and behavioral problems precluded measurements in a further 15 cases. Ultrasound measurements were also performed in 50 male and 58 female control subjects, who were matched with hospital patients for age and gender. The control subjects were randomly selected and recruited from an age/gender register of a local general medical practice. Control subjects taking hormone re-
Key Words: Bone mineral density; Broadband ultrasound attenuation; Mental retardation; Osteoporosis; Ultrasound; Velocity of sound.
Address for correspondence and reprints: Dr. R. M. Francis, Musculoskeletal Unit, Freeman Hospital, Newcastle upon Tyne NE7 7DN, UK. E-mail: [email protected] © 1998 by Elsevier Science Inc. All rights reserved.
665
8756-3282/98/$19.00 PII S8756-3282(98)00054-4
666
T. J. Aspray et al. Heel ultrasound in adults with mental retardation
Bone Vol. 22, No. 6 June 1998:665– 668
Table 1. Mean 6 SEM BUA and VOS measurements in 108 patients with mental retardation and age- and gender-matched control subjectsa Both genders Patients BUA (dB MHz21) Mean [range] difference BUA z score VOS (m/sec) Mean [range] difference VOS z score
Controls
42 6 3
78 6 2 36 [233–125] 22.1 6 0.1 20.1 6 0.1 1587 6 5 1635 6 4 48 [2131–196] 0.24 6 0.07 0.73 6 0.05
Males Patients 52 6 4
Females Controls
89 6 2 38 [233–125] 22.1 6 0.2 0.0 6 0.1 1603 6 7 1649 6 5 46 [274–176] 0.58 6 0.07 1.06 6 0.05
Patients
Controls
34 6 3 68 6 2 34 [223–91] 22.2 6 0.2 20.2 6 0.1 1573 6 7 1623 6 5 50 [2131–196] 20.06 6 0.09 0.49 6 0.06
Differences between patients and control subjects are all statistically significant (p , 0.005).
a
placement therapy or other medications for osteoporosis prevention or treatment were excluded. BUA and VOS were measured at the left calcaneus using an ultrasound machine, the CubaClinical Mark 2 (McCue Ultrasonics, Winchester, UK). In seven patients with low BUA (all less than 50 dB/MHz), who were able to travel to another hospital and who were not behaviorally disturbed, DXA bone mineral density (BMD) measurements of the lumbar spine and femoral neck were performed using a Hologic-2000 QDR. The ultrasound machine was calibrated against the manufacturer’s phantom in the factory with no significant change in BUA or VOS during the study. The coefficient of variation (CV) for phantom measurements using the machine was 0.47% for BUA and 0.11% for VOS. CV for in vivo measurements on a single subject during the study was 2% for BUA and 0.3% for VOS. Ethical approval for the study was obtained from the Northumberland Ethical Committee. Written consent was obtained from control subjects, and consent was acquired from Prudhoe Hospital residents, their relatives, or a hospital advocate as appropriate. Results are presented for all patients with mental retardation and for the 108 matched pairs of patients and control subjects as summary statistics. In addition to the individual measurements of BUA and VOS, results are also expressed in standard deviation units from the mean for young men and women (t scores) and from the mean for age-matched individuals (z scores). The normative data for the CubaClinical Mark 2 were obtained from Sheffield, UK (unpublished data). Paired t-tests were performed on the difference between ultrasound measurements in residents and controls (DATA DESK, version 4.1, Ithaca, NY).
female patients and 28 of 50 male patients had BUA measurements at least 2 SD units below the expected mean value for the patient’s age (Figures 2 and 3). Of the seven patients with mental retardation and low BUA (less than 50 dB/MHz) who also underwent DXA bone density measurements, four had a lumbar spine or femoral neck BMD more than 2.5 SD units below the mean value for young adults of the same gender (Table 2). Discussion Our study clearly shows that hospital residents with mental retardation have a marked reduction in BUA and VOS measurements at the heel, compared with age-matched control subjects. Bone ultrasound measurements are thought to reflect both bone density and architecture.7 Heel ultrasound measurements correlate relatively poorly with DXA measurements at other sites, but the correlation with BMD at the calcaneus is good.15 Ultrasound measurements at the heel also predict mechanical properties of the calcaneus in vitro.10 Furthermore, prospective studies show that ultrasound measurements predict future hip fracture risk,5,14 independent of BMD.17 The low BUA and VOS values in the hospital patients with mental retardation therefore suggest that these individuals may be at increased risk of fracture. This is supported by low DXA measurements at the spine and hip in the small group of relatively compliant patients investigated with this technique. Studies of osteoporosis in patients with mental retardation are
Results The mean age of the patients with mental retardation living at Prudhoe Hospital was 54 years (range 27– 87), whereas that for the matched pairs of patients and control subjects was 54 years (32– 83) for men and 53 years (27– 82) for women. In the total group of 92 male hospital patients, mean 6 SEM BUA was 51 6 3 dB/MHz and VOS was 1603 6 5 m/sec. In 78 female hospital patients, BUA was 34 6 3 dB/MHz and VOS was 1574 6 6 m/sec. BUA and VOS measurements on the total group of 170 patients with mental retardation were not significantly different from the 108 patients who were matched with community controls (Table 1). The control subjects had mean BUA values similar to the normal ranges provided by the manufacturers, such that the mean z score in both males and females was close to zero (Table 1). The mean VOS was higher in the control subjects than expected from the normal ranges provided by the manufacturers, but the reason for this is unclear (Table 1). Both BUA and VOS measurements were significantly lower (p , 0.005) in patients of both genders with mental retardation than in control subjects (Table 1 and Figure 1). Thirty-two of 58
Figure 1. BUA measurements at the left heel in 108 patients with mental retardation and age- and gender-matched control subjects.
Bone Vol. 22, No. 6 June 1998:665– 668
T. J. Aspray et al. Heel ultrasound in adults with mental retardation
667
Figure 2. Cumulative frequency of BUA z score for females with mental retardation and control subjects.
few, although fractures have been reported to be more common in adults with the condition.12,13 Children with cerebral palsy and mental retardation have recently been shown to have low BUA at the heel and reduced spine BMD, as measured by qCT.18 Reduction in bone density has previously been reported in a number of psychiatric conditions, including depression, schizophrenia, and anorexia nervosa.11,16 The pathogenesis of osteoporosis in these conditions is varied, but may include estrogen deficiency and hypercortisolism.11,16 There are a number of other reasons why patients with mental retardation may be at risk of developing osteoporosis and fractures. Excessive trauma due to epileptic fits may be associated with increased fracture incidence.1,12 Vitamin D deficiency may predispose to both osteomalacia and osteoporosis and is prevalent among institutionalized communities.3 Drugs that affect vitamin D status, especially anticonvulsants,6 are commonly prescribed in patients with mental retardation. Physical inactivity may be associated with osteoporosis. Hypogonadism in men and women causes osteoporosis and may be more common in this population.8 We plan to evaluate these risk factors in the group of residents studied in due course. There were technical difficulties with ultrasound measurements in patients with mental retardation because of behavioral
problems and anatomical deformities at the foot. However, the magnitude of the difference in BUA and VOS between patients and controls is highly significant and unlikely to be explained by technique alone. Institutional lifestyle in the patients with mental retardation may explain some of the difference in ultrasound measurements, as the control group by definition included mainly active individuals. It is also possible that differences in nutrition and body size may contribute to differences in BUA and VOS. Previous large studies in elderly or institutionalized individuals have not demonstrated the low or negative BUA measurements seen in the present study.5,14 The earlier studies were performed using a water bath system, whereas we chose a system using ultrasound gel for acoustic coupling, as we felt this would be more acceptable in our group of potentially disturbed patients. Nevertheless, diffraction may theoretically occur around the edges of the ultrasound transducers, particularly if there is anatomical deformity of the calcaneus or movement of the foot. We also discussed our findings with one of the investigators who developed the technique of bone ultrasound measurement. He suggested that the negative values represented a low bone mass at the limits of detection for the machine, possibly compounded
Figure 3. Cumulative frequency of BUA z score for males with mental retardation and control subjects.
668
T. J. Aspray et al. Heel ultrasound in adults with mental retardation
Bone Vol. 22, No. 6 June 1998:665– 668
Table 2. DXA bone density measurements of the lumbar spine and femoral neck in seven patients with mental retardation who had low BUA results
Gender
Age
Mobile
BUA (dB/MHz)
t score (z score)
BMD spine (g/cm2)
t score (z score)
BMD femur (g/cm2)
t score (z score)
Female Female Female Male Male Male Male
43 50 74 41 45 45 55
No No Yes Yes Yes Yes Yes
5 21 210 210 47 49 47
25.2 (24.2) 25.5 (24.2) 26.1 (23.6) 26.8 (25.7) 23.9 (22.6) 23.5 (22.4) 23.7 (22.5)
1.016 0.945 0.724 0.999 0.699 0.856 0.488
20.28 (0.08) 20.31 (0.43) 22.93 (20.57) 20.84 (20.70) 23.56 (23.33) 22.14 (21.91) 25.48 (24.99)
0.778 0.776 0.571 0.554 NDa 0.592 0.547
21.24 (20.64) 21.19 (20.15) 23.23 (20.68) 22.32 (21.17) NDa 23.51 (22.53) 23.93 (22.57)
a
Not done.
by problems with diffraction associated with foot deformity (Dr. C. Langton, Hull University, personal communication). Impaired mobility associated with low BMD localized to the heel has also been previously suggested as a possible cause for particularly low BUA at the calcaneus.12 Our data on DXA scans in subjects with low BUA may support this finding. Although four of the seven patients had low BMD at the spine or femoral neck (t score , 22.5), the two women who were immobile had disproportionately low BUA and may have low bone mass confined to the calcaneus. The BUA measurements for control subjects were similar to the Sheffield reference database, effectively excluding operator-dependent problems as the explanation for the abnormally low values in patients with mental retardation. Although the VOS measurements in our control subjects were higher than the manufacturer’s normative data, they are comparable with recently published normal ranges for adults in the UK.9 Furthermore, patients with mental retardation had significantly lower VOS measurements than age-matched control subjects recruited from the local community. There is a need to identify the causes for low bone mass in this group of individuals with mental retardation. Some potential risk factors for reduced bone density and fracture may be avoidable or treatable, such as vitamin D deficiency and hypogonadism, in both genders. Hormone replacement therapy is not always considered in hypogonadal women with mental retardation, and testosterone treatment may be withheld in hypogonadal men because of concerns about behavioral problems.2 As the population ages and more people with mental retardation live in the community, fractures are likely to pose a significant problem, so strategies aimed at fracture prevention will need to be developed.
Acknowledgments: The authors thank Dr. T. P. Berney and Dr. M. S. Bhate for allowing us to study their patients and also for helpful advice, and J. Borland and all the staff of Prudhoe Hospital for their help in the study. Reverend M. Wheelwright acted as hospital advocate. We are grateful to the staff of Castle Surgery and all those who agreed to take part in the study. The study was supported by Eli Lilly Pharmaceuticals, the National Osteoporosis Society, the British Geriatrics Society, and Procter and Gamble Pharmaceuticals.
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Date Received: July 9, 1997 Date Revised: January 21, 1998 Date Accepted: January 21, 1998