Original ArticleRepeatability of Volume and Regional Body Composition Measurements of the Lower Limb Using Dual-energy X-ray Absorptiometry
Introduction
Lower limb lymphedema (LLL) refers to swelling of the leg due to failure of the lymphatic system to support lymphatic circulation and the drainage of lymphatic fluid. It can be caused by lymphatic interruption due to, for instance, cancer treatment. LLL is associated with high levels of physical and psychosocial distress (1). No cure exists, but LLL can be managed with early diagnosis, treatment, and diligent care of the affected limb. There is no universally accepted standard definition of LLL (2). The diagnosis of LLL is typically made after a thorough history and physical examination. Widely used noninvasive measurement techniques of lymphedema include assessing volume differences between the affected and contralateral limb with water displacement (also known as water plethysmography), indirectly with circumferential measurement, a perometer (infrared measuring device), and bioimpedance spectroscopy (BIS). However, previous studies have shown poor repeatability of volume measurements with water displacement and indirectly with circumferential measurements (3). Perometers are widely used for volume measurements of lymphedema. However, perometers and BIS analysis are not widely available, which DXA scanners on the contrary are. This is due to the widespread use of DXA for measuring bone mineral density in assessing osteoporosis and other conditions that cause bone loss or affect bone composition. Our previous study showed that dual-energy X-ray absorptiometry (DXA) assessing volumes of breast cancer-related arm lymphedema and the contralateral arm had excellent repeatability and the method was superior to water displacement and circumference measurements (3). DXA scan is clinically convenient, with low cost and low radiation exposure corresponding to 4–8 µSv. For comparison, the worldwide average effective dose from natural background radiation is 7 µSv/day 4, 5.
The initial swelling and volume change of the region with lymphedema are associated with inflammation caused by protein-filled fluid in the subcutaneous tissue. This inflammation may partially explain the tissue composition changes of the affected limb over time with increasing fat deposition, and these changes can be demonstrated with DXA, which provides quantitative measurements of bone mineral content (BMC), fat mass, and lean mass; the latter encompasses the remaining tissue after BMC and fat mass have been subtracted. Swelling of an extremity due to lymphedema will primarily result in increase in lean mass, and later in fat mass (6). Other techniques of assessing tissue composition include computed tomography, magnetic resonance imaging, and BIS. However, routine clinical volume and tissue composition measurements with computed tomography, magnetic resonance imaging, and BIS are not feasible due to costs, radiation exposure, time-consuming examinations and interpretations, which all can be overcome using DXA.
The aim of this study was therefore to assess the repeatability of DXA scans for volume and regional body composition measurement of the lower limb as part of a larger investigative study. To our knowledge, the repeatability of DXA for volume and regional body composition of the lower extremities has not been reported previously.
Section snippets
Participants
The first 27 participants in a larger investigative study, in which DXA scans were performed on all 4 limbs, were included in this study: 14 women and 13 men aged 33–71 years. Inclusion criteria were weight < 136 kg (weight limit of the DXA table) and disease-free melanoma survivors with no radioisotope scan within 3 days. The patients had been treated for stage IB-III primary cutaneous melanoma with wide local excision and unilateral sentinel lymph node biopsy and/or complete lymph node
Results
The participants' characteristics are shown in Table 1. Data from 54 lower extremities were included in the study. No participants or limbs were excluded from the study. Summary statistics of mean and differences in total volume, regional BMC and fat and lean masses of the lower limb are shown in Table 2, Table 3.
Discussion
In this study, the repeatability of measuring tissue composition (measured as BMC and fat and lean masses) and total volume of the lower limb was investigated. The repeatability was excellent, and the examination was able to show physiological changes in the lean mass between the first and the second scan of 1% whereas the fat and bone mass remained unchanged as illustrated on the Bland–Altman plots (Fig. 8, Fig. 9).
The present study showed that the volume of the lower limb can be determined
Acknowledgments
Funding was received from the Department of Plastic Surgery and The Research Council at Herlev and Gentofte Hospital, and The Danish Cancer Society.
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