Clinically important change in quality of life in epilepsy

Health related quality of life (HRQOL) is recognised as an important outcome in epilepsy treatment, and various instruments have been developed to assess it in epilepsy. Typically, studies exploring the impact of epilepsy treatments on HRQOL compare the mean score of instruments among various treatment groups and assess whether the differences are statistically significant. However, it is difficult to interpret the importance of mean changes in HRQOL, regardless of their statistical significance. This is because aggregate data (group means) convey no information about the number of individuals in a group who experience clinically important change. For example, when the mean change for the group is not statistically significant or when it is lower than a prespecified minimum threshold, clinicians may erroneously conclude that the treatment has no important effects. As shown by Guyatt et al , small mean changes can conceal clinically important treatment effects in a substantial number of patients. ¹ Conversely, large mean changes can be accounted for by a small number of individuals experiencing large changes, while the majority of the group remains unchanged. ¹ Clinical interpretation of HRQOL requires a notion of what constitute clinically important, small, medium, and large changes in instrument scores in individual patients.

We quantified the amount of change in commonly used epilepsy specific and generic HRQOL instruments that patients consider as important-that is, the minimum clinically important change (MIC)-and we also obtained estimates of small, medium, and large changes in these instruments.

METHODS

Patients

We prospectively assessed 136 consecutive adults with medically refractory focal epilepsy with or without secondary generalisation who were investigated for epilepsy surgery. Patients aged 16 years or older were eligible if they could complete self administered HRQOL questionnaires. They were excluded if they had non-epileptic seizures, learning disability, progressive central nervous system disorders, or medical conditions precluding epilepsy surgery. We aimed to enrol a broad clinical spectrum of patients representative of adults with medically refractory focal epilepsy. Patients gave informed consent and the institutional ethics review board approved the study.

Health related quality of life instruments

We conceptualised HRQOL as the patients' own experience of health, and assessed by the patients' perception of change in their own health status. ² We quantified change in four HRQOL instruments. Two are epilepsy specific-the...