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Determining the minimal important difference of EQ-5D-5 L utility values in CIDP patients using data from a large
Febe Brackx1, Clémence Arvin-Berod2, Glenn Phillips3
1Services in Health Economics, Brussels, Belgium.
Purpose:
Chronic Inflammatory Demyelinating Polyradiculoneuropathy (CIDP) is a rare autoimmune disorder characterized by limb weakness and sensory disturbances. This study aimed to estimate the minimal important difference (MID) of EQ-5D-5 L utility values in CIDP patients.
Methods:
ADHERE, the largest CIDP trial to date, demonstrated the efficacy of efgartigimod. In Stage A (open-label; n = 322), patients received efgartigimod for up to 12 weeks or until evidence of clinical improvement (ECI). Patients with ECI entered Stage B, receiving efgartigimod (n = 111) or placebo (n = 110) for up to 48 weeks. An open-label extension (OLE) included 229 patients treated for up to 48 weeks. Disability was assessed using the adjusted INCAT (aINCAT) score (0-10). EQ-5D-5 L and aINCAT were recorded at baseline and end of Stage A. Perceived improvement was captured using the Patient Global Impression of Change (PGIC). Anchor-based methods were applied to estimate the MID: mean utility change for patients reporting "a little better" on PGIC; mean utility change in patients with a 1-point aINCAT decrease; regression of utility change versus aINCAT change; receiver-operating characteristic (ROC) curve. A distribution-based estimate was also derived (0.5x baseline SD).
Results:
MID estimates were 0.11 (PGIC), 0.14 (1-point aINCAT decrease), 0.10 (regression), 0.10 (ROC), and 0.14 (distribution-based). In the OLE, 66.5% of patients achieved the MID by week 12 (n = 188).
Conclusion:
The PGIC-based MID (0.11) aligns with estimates in other conditions and supports interpretation of utility changes in future evaluations. Most patients in the OLE achieved this threshold, indicating sustained quality-of-life improvement with efgartigimod.
