Assessing the validity and responsiveness of disease-specific quality of life instruments in intermittent claudication.

PURPOSE: To recommend a suitable disease-specific quality of life (QOL) instrument for use in intermittent claudication (IC) based on validity and responsiveness.
METHODS: Seventy claudicants completed two generic (SF36 and EUROQOL) and three disease-specific (CLAUS, VASCUQOL and SIP(IC)) QOL instruments prior to and 6 months after treatment (angioplasty or conservative therapy). Ankle brachial pressure indices and treadmill walking distances were measured at each assessment and International Society of Cardiovascular Surgery (ISCVS) recommended outcome measures were used to stratify the results. Construct and convergent-divergent validity was assessed for the three disease-specific QOL instruments. Responsiveness was assessed using effect sizes (effect size >0.5 is clinically significant).
RESULTS: All clinical indicators improved significantly following treatment. All five domains of CLAUS, the VASCUQOL and SIP(IC) showed highly significant spearman correlation with intermittent claudication distance (ICD) and maximum walking distance (MWD) (0.267-0.697, p=0.01), suggesting good construct validity. There was greater correlation between like domains of CLAUS and SF36 than non-like domains suggesting good convergent-divergent validity. Pain domain of CLAUS and VASCUQOL could detect mild clinical improvement significantly (effect sizes 0.55 and 0.67). Pain and everyday life domain of CLAUS and the VASCUQOL could detect moderate clinical improvement significantly (effect sizes 0.7, 0.74 and 0.56, respectively).
CONCLUSION: The three disease-specific QOL instruments (CLAUS, VASCUQOL, SIP(IC)) showed a high degree of construct and convergent-divergent validity. Amongst the three disease-specific QOL instruments, the VASCUQOL was most responsive and we would recommend its use in clinical practice.