Longitudinal proxy measurements in multiple sclerosis: patient-proxy agreement on the impact of MS on daily life over a period of two years

Abstract

BackgroundThe use of self-report measurements in clinical settings is increasing. However, in patients with limitations that interfere with reliable self-assessment such as cognitive impairment or mood disturbances, as may be the case in multiple sclerosis (MS), data collection might be problematic. In these situations, information obtained from proxy respondents (e.g. partners) may replace self-ratings. The aim of this study was to examine the value of proxy ratings at separate points in time and to assess patient-proxy agreement on possible changes in disease impact of MS.MethodsFifty-six MS patients and their partners completed the Multiple Sclerosis Impact Scale (MSIS-29) at baseline and follow-up, two years later. Patient-proxy agreement was assessed at both time points by calculating intraclass correlation coefficients (ICCs), exact and global agreement and the mean directional differences between groups. Agreement of change over time was assessed by calculating ICCs between change scores. In parallel, global ratings of both patients and proxy respondents of the extent to which the patient had improved or deteriorated over the past two years were collected to validate possible changes on the MSIS-29.ResultsAt both time points, agreement on the physical scale was higher than agreement on the psychological scale (ICCs at baseline were 0.81 for the physical scale and 0.72 for the psychological scale; at follow-up, the ICC values were 0.86 and 0.65 respectively). At follow-up, statistically significant mean differences between patients and proxies were noted for the physical scale (-4.8 ± 12.7, p = 0.006) and the psychological scale (-8.9 ± 18.8, p = 0.001). Agreement between change scores on the MSIS-29 was fair (ICC < 0.60). Our analyses suggest that the validity of measuring changes over time might be better for proxy respondents compared to patients.ConclusionProxy respondents could act as a reliable source of information in cross-sectional studies. Moreover, results suggested that agreement on change over time might be better for proxy respondents compared to patients. Although this remarkable finding should be interpreted cautiously because of several limitations of the study, it does plead for further investigation of this important topic.

Agreement of patient and physician ratings on mobility and self-care in neurological diseases

“…In contrast to existing literature, which usually finds that external assessors tend to evaluate the patient's condition as more negative (e.g., [2,19]), we found only slight differences between patients and providers at the beginning of rehabilitation at the group level and a more negative assessment by the patients at the end of rehabilitation. The exception was for the scales ''Hands and arms'' and ''Household tasks'', for which the physician gave a more negative assessment at the end of rehabilitation.…”

“…At the group level, these differences generally indicate that the proxies give a more negative assessment of the patient's condition [2,[17][18][19]. The effect sizes of these differences are slight to moderate and often lie between 0.10 and 0.50 [15,16].…”

“…A great deal of inconsistency exists with respect to other factors affecting the extent of agreement. Usually no or only slight influence is found with respect to age and gender [4,15,19,21]. Hays et al [20] find that the level of education is a factor, with less agreement for a lower level of education, while the study by Chen et al [4] found that education had no effect.…”

“…Some studies (e.g., [2,26]) find a greater degree of agreement at the end of treatment, which can be explained for example by the fact that the providers are more familiar with the patient or that the patient's condition becomes more stable; other studies [16,19] find no change in agreement. The agreement between patient and proxy regarding change scores is low for van der Linden et al [19], with ICCs between 0.30 and 0.42.…”

“…The ICCs generally lie in the upper range for observable aspects of HRQOL such as mobility and self-care and are lower for unobservable or only partially observable psychologic dimensions, such as pain and depression [17][18][19]22]. A great deal of inconsistency exists with respect to other factors affecting the extent of agreement.…”