Abstract
Changes in Quality of Life After Epilepsy Surgery: The Role of Reprioritization Response Shift.
Sajobi TT, Fiest KM, Wiebe S. Epilepsia 2014;55:1331–1338.
OBJECTIVES: Health-related quality of life (HRQOL) is an important indicator of well-being in patients with epilepsy. When assessing changes in HRQOL over time, some of the changes observed may be due to the patients’ change in the internal standards, value, or meaning that they attribute to the HRQOL domain being measured, rather than actual change, a phenomenon known as response shift. Response shifts are increasingly recognized as an important explanation for the seemingly paradoxical or counterintuitive HRQOL results often observed in chronic conditions. We investigated the presence of changing values (reprioritization response shift) in data from a surgical randomized controlled trial of patients with temporal lobe epilepsy (TLE). METHODS: Eighty patients with TLE, who were randomized to surgical and medical treatment, provided data on the epilepsy-specific 31-item Quality of Life in Epilepsy (QOLIE-31) questionnaire at baseline and 1 year after randomization. Reprioritization response shift among the seven QOLIE-31 domains was assessed using changes in the relative importance weights derived from logistic regression and discriminant analysis. RESULTS: The relative importance analysis showed a statistically significant increase over time in the importance of social function, but a significant decrease in the relative importance of seizure worry. There were no significant changes in the relative importance of the remaining five domains in distinguishing between surgical and medical group over time. SIGNIFICANCE: Patients that receive surgical treatment are more likely to experience a decrease in the valuation of seizure worry and an increase in the value of social function as compared to patients who are medically treated. Changes in expectation about seizure freedom and social function may confound the assessment of longitudinal change on these outcomes, and highlight the importance of assessing response shift and the limitations of assessing HRQOL at a single point in time or without a control group.
Commentary
Studies evaluating epilepsy therapy outcomes have traditionally focused on seizure reduction and freedom as well as number of antiepileptic drugs. Clinicians and researchers are increasingly recognizing the importance of looking beyond the seizures themselves. As the recent IOM report states, “Living with epilepsy is about much more than just seizures; the disorder is often defined in practical terms, such as challenges in school, uncertainties about social situations and employment, limitations on driving, and questions about independent living” (1). Commensurate with this idea, health-related quality of life (HRQOL) outcomes are often assessed in relation to the epilepsies and their treatments. These outcomes are typically subjective and are measured using standardized questionnaires. An epilepsy specific inventory is available and incorporates factors unique to epilepsy, such as seizure worry, memory, and medication effect (31-item Quality of Life in Epilepsy [QOLIE-31]). Given the qualitative and subjective nature of this instrument and other HRQOL measures, it is important to recognize potential biases and factors that may influence the findings. Indeed, social scientists have dedicated significant research efforts to better understanding these factors as well as developing statistical methods to control for them.
The reprioritization response shift is a well studied and published effect on the results of HRQOL research. When asked about HRQOL measures, one is influenced by phenomena that may change the perception of one's health and quality of life. This concept is broadly termed “response shift.” Response shift refers to a change in an individual's self-evaluation as a result of a change in respondent's internal standards, values or priorities, and conceptualization of quality of life (2). Simplistically, one may view HRQOL measures differently, depending on their current health, treatment, social situations (such as support, ability to drive, ability to work), and priorities that may have changed (e.g., family may be more important if one's health has changed). These changes can be particularly evident when looking at longitudinal HRQOL data. Social scientists have defined three forms of response shift (2): The first is a reconceptualization or redefinition of the target construct over time. The second is a recalibration or change in an individual's internal standards of specific measures, which often results in an underestimation of the change in studied measures. The third form is a reprioritization or change in an individual's values, which may affect the importance of a specific measure, particularly in relation to other measures.
Response shift has been studied in multiple chronic health conditions, including cancer, stroke, multiple sclerosis, diabetes, palliative care, inflammatory bowel disease, orthopedics, and chronic disability. Despite the increasing number of publications on HRQOL outcomes in patients with epilepsy, however, no study has previously assessed the impact of response shift. Understanding its effect may explain unexpected findings and should be considered.
In the landmark randomized controlled trial (RCT) evaluating medical versus surgical therapy, clinically significant changes in HRQOL were associated with treatment type and not seizure status (3). This association contradicts our understanding of the relationship between seizure frequency and QOL and may be influenced by response shift. Sajabi and colleagues are to be commended for further investigating whether response shift was present among the QOL measures studied in the previously published RCT.
In the RCT of surgery for temporal lobe epilepsy, 80 subjects with antiepileptic drug (AED) resistant temporal lobe epilepsy were randomized to either medical or surgical therapy (1:1) at a single center. HRQOL data was gathered using self-administered generic instruments and the QOLIE-31 given at baseline, 3, 6, 9, and 12 months. A relative importance analysis method was done using logistical regression and discriminant analysis to assess reprioritization response shift between baseline and one year. As discussed earlier, the prioritization response shift refers to a change in how one views a specific HRQOL measure. The relative importance analysis uses group data and is based on the statistical significance of changes in the relative importance of specific HRQOL domains over time. In this specific case, was there a change in the studied HRQOL measures before and after the RCT, that is, baseline compared to one year? Seven domains derived from the QOLIE-31 and not the generic instruments were studied: overall quality of life, social function, energy, emotional well-being, seizure worry, memory, and medication effect. The authors found that when comparing the medical and surgical groups, those treated with surgery had a significant increase over the year of study in the relative importance of social function and a decrease in the relative importance of seizure worry. In other words, the surgical group experienced a response shift in social function and seizure worry during the study. There was no change or reprioritization response shift on the other domains.
In the RCT of surgery for temporal lobe epilepsy, the surgical group was more likely to be seizure free. Fifty-eight percent compared to 8% were free of seizures impairing awareness (p < 0.001). Thirty-eight percent compared to 3% were free of all seizure types (p < 0.001). Both were intention-to-treat analyses. The difference in seizure control likely contributed to the described reprioritization response shift as well as the originally reported findings that HRQOL changes were independent of seizure status.
The results of this study highlight the need for rigor when analyzing QOL data. In addition, the findings emphasize that QOL measures at a single point in time do not provide a full assessment of the tested measures. QOL data can be subject to many influences that may change secondary to variable perceptions of disease state and treatment.
This analysis reveals that patients with refractory temporal lobe epilepsy placed more importance on social function than on seizure worry 1 year after surgery. This change was not seen in the medical group. These findings explain why in the previously published analysis (3), QOL did not correlate with seizure status. QOL studies in patients with epilepsy are important, as they provide a more global picture regarding how the patient is doing. It is, however, necessary that all potential confounding factors and biases are assessed. The response shift is one such factor.