From a presentation at the 2000 Conference of the British Lymphology Society
Dr. Anthony Stanton
This is most important: ask the appropriate questions and then carefully examine the limb.
History of the presenting complaint.
Clinical examination of the limb (always compare with the opposite limb):
1. Inspection 2. Palpation
Consider size, distribution of swelling along the limb (any hand/finger involvement? any extension of swelling to the adjacent trunk?), shape (is the arm or leg still arm- or leg- shaped?), skin condition, and consistency of swelling (soft, firm, hard, fatty; 'brawny' strictly means muscular or fleshy but is used to mean firm or hard, and indicates a degree of fibrosis).
1. Water displacement
2. Tape measure
3. Volumeter (Perometer)
Unsatisfactory. It is time-consuming, messy, unsuitable with some skin problems, transmission of infection is possible, a high level of patient co-operation is required, and it is difficult to immerse the limb to precisely the desired level. It is the only method available to determine hand and foot volume accurately.
Limb circumference (and hence volume) is underestimated if the tape is pulled too tight - a standard weight can be applied to the end of the tape but, above all, consistency of technique is needed. Particular care is needed at elbow/knee region (i.e. concave rather than convex surfaces) and where there are loose skin folds. Circumferences may be measured at 4-cm intervals along the longitudinal axis (not along the surface) of the limb. This interval is a reasonable compromise but other spacings are possible. The formula for a truncated cone or a cylinder may be used, but be consistent! These formulae are discussed in Stanton et al. (1997) and Stanton et al. (2000).
The Perometer is easy and quick to operate, accurate, and reproducible. The limb is inserted into a vertically- or horizontally- orientated frame that emits two parallel arrays of infra-red light beams at right-angles to each other. The limb casts shadows that are sensed by receivers on the opposite two sides of the frame to the light emitters, and two transverse diameters of a 'slice' of the limb are measured. The frame is moved along the length of the limb, enabling similar measurements to be made every 3 mm. A circular or elliptical cross-section is assumed, and volume calculated accordingly. Limb volume, percentage difference between selected measurements, contour, and cross-sectional area can be displayed. It is difficult to measure the most proximal part of the upper arm or thigh, and the Perometer cannot measure the hand or foot accurately; further disadvantages are its large size and cost. The Perometer has been recently modified to enable detection of convex contours of the limb surface (the '3D-LED-scanner system'). Volume is calculated from a large number of diameter measurements instead of just two at right angles, but it is not necessarily more accurate than the earlier version.
Use of the tape measure (to some extent) and water displacement (in particular) are prone to error. The Perometer results in only very small errors and is becoming the new 'gold-standard'. Deviation of the limb from circular or elliptical cross-section can in theory result in errors with both the Perometer and tape measure. The area of a cross-section deviating from the circular is less than that of a truly circular cross-section of equal circumference. Measurement of circumference with a tape therefore tends to result in overestimation, but compression of soft tissues by pulling it too tight (greater for swollen limb than normal limb) will result in underestimation. The greater the deviation of the limb from the theoretical shape assumed in the formula for calculation of volume, the greater the potential for error.
With water-displacement, errors arise mainly from immersion of the limb to different levels with each measurement. The average of three measurements is more reliable than a single measurement. With the Perometer, errors are small and there is a tolerance of the limb being off-centre within the measuring frame. Longitudinal positioning is more important.
Digital (thumb) pressure is used to test for the presence of pitting oedema. This is a subjective test for increased interstitial fluid mobility. Tonometry placed this concept on a more objective basis and originally involved the use of a mechanical device to measure the depth of compression of the tissues by an applied mass; this was read from a scale after fixed time period. The electronic tonometer developed by Bates et al. (1994) records the initial rapid deformation and the subsequent slow indentation caused by an applied mass.
The initial deformation was found to be same in swollen arms as in the opposite normal arms, but the slow deformation was 4-fold greater and its time constant was 3-fold greater. Further approaches have been the measurement of the gradually decreasing resistive force of the tissue following quasi-instantaneous compression to 4 mm (fixed), measurement of mechanical pulse wave velocity, and measurement of stiffness and elasticity of skin (see Stanton et al. 2000). Modified Harpenden skinfold callipers Roberts et al. (1995) have been used to detect oedema at the posterior axillary fold in breast cancer treatment related arm lymphoedema. Displacement of interstitial (oedema) fluid occurs with continued application. This method is not useful at other anatomical sites.
CT can be used to give the cross-sectional area of the limb and compartments within it (skin, subcutis, muscle), together with density measurements. CT demonstrates the characteristic (but not pathognomonic) honeycomb pattern of the subcutis in lymphoedema (fibrosclerotic septa). The radiation dose is a drawback. Dual energy X-ray absorptiometry (DEXA) has been used to study soft-tissue composition and could have a role in lymphoedema. Magnetic resonance imaging has also been used in lymphoedema. It is expensive and the confined space inside the scanner may cause claustrophobia. US has been used to assess skin thickness in lymphoedema, and is probably superior and more versatile than skinfold callipers.
Measurement of the impedance spectrum to a small current passed at a single frequency or a range of frequencies through the body, or part of the body, provides information on total water content and extracellular water content. Most studies have analysed whole body composition, e.g. in renal patients. Multiple frequency bioelectrical impedance analysis has been applied in lymphoedematous limbs, but one drawback is that it cannot detect change in the non-fluid component of swelling (fibrous tissue) (Mikes et al., 1999).
Bates DO, Levick JR, Mortimer PS. Quantification of rate and depth of pitting in human edema using an electronic tonometer. Lymphology 1994; 27: 159-172. Mikes DM, Cha BA, Dym CL, Baumgaertner J, Hartzog AG, Tracey AD, Calabria MR. Bioelectrical impedance analysis revisited. Lymphology 1999; 32: 157-165. Roberts CC, Levick JR, Stanton AWB, Mortimer PS. Assessment of truncal edema following breast cancer treatment using modified Harpenden skinfold callipers. Lymphology 1995; 28: 78-88. Stanton AWB, Northfield JW, Holroyd B, Mortimer PS, Levick JR. Validation of an optoelectonic volumeter ( Perometer®). Lymphology 1997; 30: 77-97. Stanton AWB, Badger C, Sitzia J. Non-invasive assessment of the lymphedematous limb. Lymphology 2000; 33: 122-135.
Lymphology Conference 2000