The Rasch-transformed gastrointestinal symptoms rating scale in myotonic dystrophy type 1 (RT-GSRS-DM1)

Area of Science:

• Neurology
• Gastroenterology
• Medical Informatics

Background:

• Myotonic Dystrophy type 1 (DM1) is a multisystemic neuromuscular disorder with significant, yet under-assessed, gastrointestinal (GI) symptoms impacting patient quality of life.
• Currently, no disease-specific GI symptom questionnaire exists for DM1 patients.
• The established Gastrointestinal Symptoms Rating Scale (GSRS) lacks validation using modern clinimetric standards for DM1.

Purpose of the Study:

• To evaluate the suitability of the GSRS for DM1 patients using Rasch analysis.
• To develop a disease-specific, interval-level GI symptom measure for DM1.

Main Methods:

• Rasch analysis was employed to assess item fit, threshold ordering, differential item functioning (DIF), local dependency, and unidimensionality.
• Model fit was determined using chi-square statistics, item and person fit residuals, and the Person Separation Index (PSI).

Main Results:

• The initial GSRS data from 403 DM1 patients did not meet Rasch model expectations.
• Three items (hard stools, heartburn, diarrhea) were removed; nausea was split by age; constipation was retained despite misfit due to clinical relevance.
• The final model did not fully meet Rasch requirements, though an acceptable Person Separation Index (0.76) was achieved.

Conclusions:

• Measuring GI symptoms in DM1 presents significant challenges.
• This study represents a crucial initial step toward developing a more accurate and patient-centered GI symptom measure for DM1.
• Further research is necessary to create a validated questionnaire that accurately reflects the patient experience in DM1.