Assessing the Relationship of Patient Reported Outcome Measures With Functional Status in Dysferlinopathy: A Rasch Analysis Approach

Abstract

Dysferlinopathy is a muscular dystrophy with a highly variable functional disease progression in which the relationship of function to some patient reported outcome measures (PROMs) has not been previously reported. This analysis aims to identify the suitability of PROMs and their association with motor performance.Two-hundred and four patients with dysferlinopathy were identified in the Jain Foundation's Clinical Outcome Study in Dysferlinopathy from 14 sites in 8 countries. All patients completed the following PROMs: Individualized Neuromuscular Quality of Life Questionnaire (INQoL), International Physical Activity Questionnaire (IPAQ), and activity limitations for patients with upper and/or lower limb impairments (ACTIVLIMs). In addition, nonambulant patients completed the Egen Klassifikation Scale (EK). Assessments were conducted annually at baseline, years 1, 2, 3, and 4. Data were also collected on the North Star Assessment for Limb Girdle Type Muscular Dystrophies (NSAD) and Performance of Upper Limb (PUL) at these time points from year 2. Data were analyzed using descriptive statistics and Rasch analysis was conducted on ACTIVLIM, EK, INQoL. For associations, graphs (NSAD with ACTIVLIM, IPAQ and INQoL and EK with PUL) were generated from generalized estimating equations (GEE). The ACTIVLIM appeared robust psychometrically and was strongly associated with the NSAD total score (Pseudo R ² 0.68). The INQoL performed less well and was poorly associated with the NSAD total score (Pseudo R ² 0.18). EK scores were strongly associated with PUL (Pseudo R ² 0.69). IPAQ was poorly associated with NSAD scores (Pseudo R ² 0.09). This study showed that several of the chosen PROMs demonstrated change over time and a good association with functional outcomes. An alternative quality of life measure and method of collecting data on physical activity may need to be selected for assessing dysferlinopathy.

Keywords: PROMs; clinical outcome assessments; dysferlinopathy; limb girdle muscular dystrophy; quality of life.

Figure 1

Threshold map showing all items ordered in the ACTIVLIM Scale in order of difficulty. Threshold map for items in ranked order of difficulty according to Rasch analysis. “Impossible” labeled 1; “With difficulty” labeled 2; “Easy” labeled 3. There were no reversed thresholds. This is why the figure legend suggested that disordered thresholds will be labeled with a double asterisk but none are disordered. The implication of this is that as a person's functional ability increases (move left to right) they would be more likely to score higher in a consistent and hierarchical way for all questions.

Figure 2

Person–item location distribution for the EK scale. Targeting of the patient sample (top) to the EK items (bottom). The figure shows the adequate targeting between the distribution of person measurements (upper histogram) and the distribution of item locations (lower histogram). There are no ceiling/floor effects indicated by the range of the person measurements (upper histogram “blocks”) falling within the item locations (lower histogram “blocks”).

Figure 3

Association between Total NSAD score and ACTIVLIM. NSAD, North Star Assessment for Limb Girdle Type Muscular Dystrophies; ACTIVLIM, Measure of Activity Limitations in Daily Living.

Figure 4

Association between total NSAD score and IPAQ. NSAD, North Star Assessment for Limb Girdle Type Muscular Dystrophies; IPAQ, International Physical Activity Questionnaire.

Figure 5

Association between total NSAD score and INQoL. NSAD, North Star Assessment for Limb Girdle Type Muscular Dystrophies; INQoL, Individualized Neuromuscular Quality of Life Questionnaire.

Figure 6

Association between total PUL score and EK scale. EK, Egen Klassification questionnaire; PUL, Performance of Upper Limb Scale.