Abstract

Summary Background: Bioimpedance spectroscopy (BIS) is used to assess lymphedema by measuring limb fluid content as an electric current passes through cell membranes and tissues. There are two primary device modalities, through which BIS is used clinically: single-segment bioimpedance (SSB) and multi-segment bioimpedance (MSB), which differ in their mechanisms of gathering measurements. In this cross-sectional study, we study the difference between SSB and MSB in evaluating lymphedema by referencing the results with indocyanine Green (ICG) lymphography.

Methods: Patients with unilateral and bilateral lymphedema, presented to our department, were assessed with both SSB and MSB as part of a pre-lymphatic surgery evaluation between May 1, 2017, and November 31, 2017. Patients were imaged with ICG lymphography to con- firm lymphedema presence. Standardized device measurement outputs from SSB and MSB were recorded and statistically analyzed.

Results: SSB was more sensitive (0.9) than MSB (0.75) for unilateral lymphedema. However, MSB had the added ability to assess patients with bilateral lymphedema with a sensitivity of 0.56 and specificity of 0.60. Furthermore, MSB had a stronger correlation with relative disease severity compared to SSB and quantified the differential extents of edema. In comparison, SSB provided a manipulated number, which was derived from a comparison of the abnormal to the normal limb. Medical staff reported MSB being easier to perform, and all patients reported the MSB measurement experience being more favorable.

Main findings

• This study compared single segment bioimpedance (SSB) using the Impedimed U400 with multi-segment bioimpedance (MSB) via the InBody 770. This was benchmarked against ICG lymphography.
• Thirty-five patients presented with the possible unilateral limb or bilateral lymphedema.
• The diagnostic performance of both SSB and MSB was examined.
• This study compared the ability of two bioimpedance devices (MSB and SSB) to assess lymphedema, using ICG lymphography as a reference standard. SSB was more sensitive (0.9) than MSB (0.75) for unilateral lymphedema. However, MSB was able to assess patients with bilateral lymphedema with a sensitivity of 0.56 and specificity of 0.60. These results imply that SSB has a higher ability to rule out unilateral lymphedema than MSB, but MSB can assess patients with bilateral lymphedema. No clinically significant differences were seen among the cases with unilateral versus bilateral disease, indicating the difference in sensitivity to be related to the bioimpedance devices themselves and that bioimpedance technology may not be suitable to rule in or rule out lymphedema on its own.
• There was also a high rate of false negatives (0.67 for SSB and 0.83% for MSB). The authors hypothesize this is because the fluid in the limbs can be manipulated through physical maneuvers (e.g., manual lymphatic drainage and external compression), in therapeutic efforts to reduce edema. Limb fluid content can also vary throughout the day. In order for bioimpedance to detect lymphedema, the patient’s limb must be edematous when measured. In early disease, edema is highly manipulatable and fluctuates with activity. Therefore, patients with early or subclinical disease may not be edematous in the clinic, resulting in false negatives, even though there is underlying lymphatic damage. As disease severity increases, bioimpedance results may be more reliable and reflect the changes in the lymphatic system. The findings in this study and recent studies demonstrate the high false-negative rate of bioimpedance technology and contradict the ability of bioimpedance technology to detect early (Campisi stage I) and subclinical (stage 0) disease.
• When comparing the results of the two technologies against each other, a strong correlation between SSB and MSB was not seen.
• The authors conclude in this study, both SSB and MSB had high false-negative rates for lymphedema diagnosis. However, MSB is notably easier to perform, can detect bilateral disease, and objectively quantifies limb fluid volume, allowing for disease tracking and assessment of surgical and rehabilitative treatment efficacy. Therefore, clinical management of lymphedema with MSB may be preferred over SSB, especially in patients with bilateral lymphedema, and should always be considered with clinical context and other diagnostic tools. These findings are irrelevant with the availability of Impedimeds SOZO device.