OBJECTIVES:

Off-episodes (OEs) occur in Parkinson’s Disease (PD) when levodopa stops working and symptoms worsen. Currently available patient-reported outcome measure may not adequately capture the impact of OEs on health-related quality of life (HRQL) and daily functioning. This study summarizes the development of a measure of OE impact on HRQL and daily functioning in patients with PD, the OFF Episode Quality of Life Impact Scale (OFFELIA).

METHODS:

Participants completed cross-sectional health and disease questionnaire “Impact and Communication on OFF Periods” as part of standard schedule of activities at Fox Insight, an online data platform for people with PD developed by the MJ Fox Foundation. Psychometric properties were examined, including distribution, dimensionality (using exploratory factor analysis (EFA) and known-group comparison. Poorly fitting items were identified using information functions and category characteristic curves from an item response theory (IRT) model. Differential item functioning (DIF) was tested across key subgroups (i.e. sex and US vs non-US respondents).

RESULTS:

569 individuals with PD completed the questionnaire. The distribution of responses of 18 candidate items did not suggest floor or ceiling effects. EFA identified two factors: first factor (13 items) represented functioning and the second factor (5 items) represented psychological well-being. IRT indicated that the response levels of most of the items were ordered, but there was some evidence of DIF by sex. Overall, 15 items worked well, 2 items had mixed evidence, and 1 item performed poorly (employment). Known groups comparisons based on hours of off-time indicated that OFFELIA subscales were more sensitive than existing generic and condition-specific measures.

CONCLUSIONS:

Initial evidence supports the validity and reliability of OFFELIA, a new instrument for evaluating the impact of OEs on HRQL and functioning in PD patients, and demonstrates its potential to better capture impact of OEs and clinical benefits of new and existing therapeutic strategies.