Objectives: To evaluate concurrent and construct validity for the Simplified Water Displacement Instrument (SWDI), an instrument for measuring arm volumes and arm lymphedema as a result of breast cancer surgery.
Design: Validity design.
Setting: Hospital setting.
Participants: Women (N=23; mean age, 64+/-11y) were examined 6 years after breast cancer surgery with axillary node dissection.
Interventions: Not applicable.
Main outcome measures: The SWDI was included for measuring arm volumes to estimate arm lymphedema as a result of breast cancer surgery. A computed tomography (CT) scan was included to examine the cross-sectional areas (CSAs) in square millimeters for the subcutaneous tissue, for the muscle tissue, and for measuring tissue density in Hounsfield units. Magnetic resonance imaging (MRI) with T2-weighted sequences was included to show increased signal intensity in subcutaneous and muscle tissue areas.
Results: The affected arm volume measured by the SWDI was significantly correlated to the total CSA of the affected upper limb (R=.904) and also to the CSA of the subcutaneous tissue and muscles tissue (R=.867 and R=.725), respectively (P<.001). The CSA of the subcutaneous tissue for the upper limb was significantly larger compared with the control limb (11%). Tissue density measured in Hounsfield units did not correlate significantly with arm volume (P>.05). The affected arm volume was significantly larger (5%) than the control arm volume (P<.05). Five (22%) women had arm lymphedema defined as a 10% increase in the affected arm volume compared with the control arm volume, and an increased signal intensity was identified in all 5 women on MRI (T2-weighted, kappa=.777, P<.001).
Conclusions: The SWDI showed high concurrent and construct validity as shown with significant correlations between the CSA (CT) of the subcutaneous and muscle areas of the affected limb and the affected arm volume (P>.001). There was a high agreement between those subjects who were diagnosed with arm lymphedema by using the SWDI and the increased signal intensity on MRI, with a kappa value of .777 (P<.001). High construct validity for the SWDI was confirmed for arm lymphedema as a volume increase, but it was not confirmed for lymphedema without an increase in arm volume (swelling). The SWDI is a simple and valid tool for estimating arm volume and arm lymphedema after breast cancer surgery.