Historical Review and Clinical Uses of Skin Indentation to Assess Limb Lymphedema.

Limb lymphedema occurs when the drainage capacity of the limb's lymphatic system is less than needed to remove fluid filtered from the capillary network. This happens due to reduced lymphatic network function or increased resistance to lymph flow within the network. Upper extremity lymphedema may result from breast cancer treatment, and lower extremity lymphedema may occur after treatments for gynecological or prostate cancer. There are multiple other causes of limb lymphedema, with filariasis being the greatest cause worldwide. Over time, lymphedema causes changes in the skin and underlying tissue, which affect the tissue's mechanical properties. Consequently, measurements of changes in the skin's compressibility may help evaluate the magnitude of progressive increases in lymphedema or help evaluate treatment-related improvements. A noninvasive parameter to assess such changes is the skin's tissue indentation resistance (TIR), expressed as the tissue indentation force (TIF) divided by the tissue indentation distance (TID). The TIR increases as the tissue becomes more fibrotic and decreases with effective treatment. This review aims to describe the various indentation methods and their applications and report on the clinical findings and utility of such measurements related to limb lymphedema due to any cause. Fortuitously, the author has direct experimental experience in this area. Three databases (Web of Science, PubMed, and Embase) were searched for peer-reviewed, original study articles on skin indention in limb lymphedema written in English. After screening the initial 236 articles, 50 studies were retrieved and evaluated for relevancy. Of these, 27 met the inclusion criteria and were relevant. In 18 studies, indentation was used to evaluate lymphedema treatment, with 11 using a fixed TIF and 7 using a fixed TID device. The remaining nine studies used indentation to characterize aspects of established limb lymphedema were evaluated. The present review's findings and the images provided clarify the evolution of tissue indentometry as an adjunctive tool in assessing limb lymphedema over the past 38 years. Its uses range from evaluating naturally occurring changes in lymphedematous skin using shallow and deep indentations to using these measures to evaluate various lymphedema treatment modalities. In all cases investigated, whether indentometry was used alone or in combination with other lymphedema assessment tools, it proved helpful in characterizing the lymphedema state in its various stages and judging the efficacy of various treatment modalities. The choice of which type of device to use in a given setting mainly depends on the specific nature of the intended measurement purpose. The present review provides relevant information to help make such choices.