Problems in measuring lymphedema:
(1) With lymphedema the extracellular fluid increases. This is distributed throughout the arm and hand. It may not be clinically evident until considerable fluid has accumulated.
(2) Body water volumes in limbs or individual body segments cannot be determined by isotope dilution techniques.
(3) The volume of the arm can be measured by recording the circumference over the entire length of the arm, but this is relatively insensitive and time consuming, as well as subject to measurement errors. It is also affected by differences due to other causes, such as muscle size differences associated with hand sidedness.
(4) Imaging studies can be done, but can be expensive for monitoring over time, and usually requires multiple visits to an imaging center.
(5) Fluid displacement for measuring volume tends to be inconvenient and have poor patient compliance.
Method for Multiple frequency bioelectrical impedance analysis (MFBIA): A very low AC current is passed through the arm, with the impedance to its flow over the frequencies from 4 kHz to 1 MHz recorded. From the graphical plot the resistance at 0 frequency (R0) and the impedance at the characteristic frequency (Zc) can be estimated. The resistance is lower if the extracellular fluid is greater.
ratio of the extracellular water in the affected limb to that of the unaffected limb =
= ratio of the resistance at 0 frequency for the unaffected limb to that of the affected limb
Interpretation:
• In Figure 1 (Cornish et al, 1996) the ratio for normal controls is from 0.95 to 1.10. For women with lymphedema, the ratio was > 1.15 (up to 2.0).
• In practice the ratio is compared to ratios from a normal control population corrected for limb dominance. A ratio > (mean + 3 SD) indicates lymphedema.
