MEASUREMENT OF LIMB CIRCUMFERENCE

Limb circumference is measured from a fixed point such as the tip of the long finger or from anatomic landmarks such as the patella or the olecranon (Fig. 24-1). Identification of local landmarks can be problematic in lymphedematous patients, because they may not be readily palpable. Furthermore, landmark descriptions may have various interpretations, which can lead to confusion and inaccuracy. For example, the patella can be measured from the proximal end, the distal end, or the middle. This can make a significant difference, particularly when measurements are repeated and compared at different time points. Limb circumference as a means of measurement has been criticized because of inconsistencies in tape measure tension and placement from one measurement to the next. Although measurements at specified intervals from a fixed point may seem to be a more accurate technique, Taylor et al ⁷ found excellent correlation between measurements taken in reference to fixed anatomic landmarks and plethysmography.

MEASUREMENT OF LIMB VOLUME

The most widely accepted measure of lymphedema is limb volume. The affected limb can be compared with the unaffected limb, or measurements of the affected limb can be compared before and after interventions or events that led to the lymphedema. Volumes are most accurately measured by plethysmography or water displacement ⁸ – ¹⁰ (Fig. 24-2). However, defining and replicating the upper level for immersion can be difficult, and water displacement is not convenient for routine clinical use.

Brorson and Höijer ¹¹ followed 10 women with unilateral upper extremity lymphedema after breast cancer treatment. They calculated volume indirectly by circumference measurements (CM), using the formula for a truncated cone. The authors developed two Excel-based formulas of the truncated cone: one for fixed 4 cm intervals, leading to 10 volume segments (VS) (CM-10-VS), and one for varying intervals, leading to four volume segments (CM-4-VS). Plethysmography yielded greater volumes, because the hand was included, but excellent correlation was observed between volumes measured by plethysmography and volumes measured by limb circumference from a fixed point. No difference was noted between CM-10-VS and CM-4-VS. In my practice I have adopted the CM-10-VS method, because in my experience, it is simple, reproducible, and repeatable, regardless of who obtains the measurements. For the upper limb, circumference is measured at 4 cm intervals from the tip of the long finger, and for the lower limb, similar measurements are taken at 4 cm intervals from the tip of the second toe.

A Perometer (Pero-System) is an optoelectronic imaging device designed to measure the volume of an object. It is ideally suited for measuring limb volume. It consists of a square measuring frame that contains rows of infrared light–emitting diodes on two adjacent sides and rows of corresponding sensors on the other two sides ¹² (Fig. 24-3). Two rows of measurement arrays are placed at a 90-degree angle to each other. Each of them determines an object diameter and its position inside the frame. The patient sits at one end of the Perometer, with the hand or foot resting centrally on an adjustable support or footplate. The frame is then moved along the length of the arm or leg, from the wrist to the axilla or from the ankle to the thigh. When the frame is moved manually, the diameters and positions are determined in short distances along the object. The collected data are not influenced by the position of the measured object within the frame. A computer produces a volume picture of the entire limb by using the cross-sectional information obtained from the biplanar shadow of the limb in the device. The collected data can be saved and analyzed. Data generated by a Perometer can be exported into other programs such as word processing programs, spreadsheets, or other standard software.

Perometry has been rigorously assessed by comparison with other methods and is considered more accurate than tape measurements. ¹² , ¹³ In various studies it has proved highly reproducible, accurate, and reliable. ¹⁴ This technology is safe and fulfills many of the criteria for an ideal measurement tool. However, it is not inexpensive or easily accessible.

NUANCES OF CIRCUMFERENCE AND VOLUME MEASUREMENTS

One of the biggest confounders of circumference and volume measurements is that causes of increased volume other than lymphedema are not taken into account. For example, breast cancer patients tend to gain weight after having chemotherapy. ¹⁵ Measurement of changes in limb circumference or limb volume measurements alone is not helpful in distinguishing between increases from lymphedema and other causes. This confounder can be somewhat controlled in patients with unilateral lymphedema by comparing the affected side with the contralateral, normal limb. In patients with bilateral lymphedema, however, this method is not as useful.