and genetic forms of edema. In children being evaluated for lymphedema, other vascular and imaging studies are necessary because primary lymphedema can occur in combination with many vascular abnormalities and other organ defects. The specific tests needed should be determined by a specialist in lymphedema. A new technique for imaging lymph vessels is Near Infra-Red Florescence Imaging (NIR) using a substance known as indocyanine green (ICG).82,171-175 The ICG is injected into the skin and immediately imaged with a dynamic (real time) infrared florescence camera. With NIR-ICG, even very small lymphatic vessels can be seen. The study is dynamic which means that the actual function of the lymphatic vessels can be analyzed. Diseased lymphatics that do not contract (or pulse) normally can be seen with NIR-ICG. ICG is a green dye that has been used safely in other areas of the body such as the liver and eyes. It can be used in very small amounts to image the lymphatics. NIR-ICG can diagnose lymphedema and find abnormalities at an early stage, possibly before swelling is obvious. Although this technique shows promise for the diagnosis of lymphedema, it is currently available at very few centers, most of which are involved in research. Measures of Volume Measures of limb (arm and leg) volume have been the standard way of detecting lymphedema for years and have been shown to be accurate when properly done.156,157,161,170 Enlargement of the limb (increase in volume) is the end result of fluid building up in the tissues. Therefore, volume measurements are used to quantify the presence and severity of lymphedema and follow the response to treatment. Volume is measured by 3 main methods: tape measurements, perometry, and water displacement.170 Tape measurements are taken at defined intervals, using geometric formulas to calculate the total volume. This technique can be accurate if it is done in precisely the same way each time, and is most accurate when the same person takes the measurements each time. Perometry uses an infra-red optical electronic scanner and computer to calculate the volume of the body part. Perometry is accurate if the body part is positioned exactly the same way each time and the machine has been calibrated for accuracy. Perometry has been used for a decade in research on lymphedema and has been accurate when compared to the long used ‘gold standard’ of water displacement.149 Perometry has been demonstrated to detect as little as a 3% change in limb volume in breast cancer survivors followed over time.207 Water displacement, the bench ‘gold standard’ for assessing volume, is rarely used these days due to its inconvenience. The body part to be measured is immersed in a large cylinder and the water that is pushed out (displaced) is measured. All of these volume methods are effective and accurate when done properly.170 They are most accurate on arms and legs. Measures of volume cannot differentiate lymphedema from other types of edema and do not determine when temporary post-operative arm edema becomes chronic lymphedema. Although tape measurements have been developed for head and neck,78 they are not true volume measurements, nor have they been standardized. They are best used for following the effects of treatment rather than making a diagnosis. Electrical Conductance Testing (BIS) Bioimpedance Spectroscopy (BIS) is a method for measuring water content in tissues. It has been used for many years to assess the total water content of the body and body composition for fitness and weight loss purposes. BIS is now available to measure interstitial fluid as a component of assessment leading to the diagnosis of lymphedema.144,148,149 BIS has been shown to provide reliable data to be used in the diagnosis of breast cancer-related lymphedema.150 BIS can detect early changes associated with lymphedema.162,164 BIS is done by passing a small, painless, electrical current through the limb and measuring the resistance to current (impedance). The machine uses certain electrical current frequencies to determine if more fluid exists as compared to the contralateral limb. It does this by comparing the difference in resistance to electricity passed through interstitial fluid compared to intracellular fluid. BIS currently is done on the whole limb since the resistance to current flow for standard technique is calculated to the length of the body part. The higher the water content in the interstitial tissue, the lower the resistance (impedance). BIS may show promise for detecting smaller areas of localized lymphedema, but this application has not been subjected to adequate study to recommend it.206 BIS is not as accurate in advanced, fibrotic edema. As in measures of volume, BIS cannot differentiate lymphedema from other types of edema and does not determine when temporary post-operative arm edema becomes chronic lymphedema.145,170,191
Posted on: Tue, 23 Jul 2013 14:13:37 +0000
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