The American Neurogastroenterology and Motility Society Gastroparesis Cardinal Symptom Index-Daily Diary (ANMS GCSI-DD): Psychometric Validation and Meaningful Change Threshold in Patients with Idiopathic or Diabetic Gastroparesis

Introduction: The American Neurogastroenterology and Motility Society Gastroparesis Cardinal Symptom Index-Daily Diary (ANMS GCSI-DD) is a patient-reported outcome (PRO) instrument for gastroparesis. This study evaluated the psychometric properties of the ANMS GCSI-DD and determined a meaningful change threshold using the data from a phase 2b trial in adults with moderate-to-severe idiopathic or diabetic gastroparesis (DG).

Methods: The psychometric properties of ANMS GCSI-DD were analyzed using other clinician- and patient-reported outcomes from 242 patients during the 12-week trial. Trial exit interviews were conducted in a cohort of 32 patients to capture their perspectives on meaningful change from the trial.

Results: ANMS GCSI-DD demonstrated good performance: unidimensionality scores exhibited good fit; internal consistency reliability was >0.70; test-retest reliability was above 0.90, and convergent validity showed strong correlations (0.70-0.90) with overall severity rating and moderate correlations (0.30-0.70) with other outcomes. ANMS GCSI-DD scores discriminated among groups with varying severity of gastroparesis symptoms in known-groups validity (p < 0.001) and were responsive to symptom improvement. Triangulation of the quantitative anchor-based estimates of 0.9-1.4 category points as a meaningful change in the ANMS GCSI-DD composite score, and the qualitative exit interview findings of 0.5-1.5 as meaningful change, supports a one-point change on a five-point scale (0-4) as the meaningful change threshold.

Conclusion: The ANMS GCSI-DD is a reliable and valid PRO instrument to employ in clinical development for patients with moderate-to-severe idiopathic or DG, and a one-point score change in the ANMS GCSI-DD composite score is recommended as a meaningful change threshold of symptom change.