Investigating instruments for evaluation of gastrointestinal burdens in patients with systemic mastocytosis: an exploratory multimethod study

OBJECTIVES: Systemic mastocytosis (SM) is a rare hematopoietic disease, in which gastrointestinal (GI) problems are common. There are no valid instruments for assessing GI problems in patients with SM. As the symptoms often mimic irritable bowel syndrome (IBS), the objective was to assess the validity of instruments designed to measure IBS related GI problems in this group of patients. METHODS: The study was performed as an exploratory multimethod study. The Gastrointestinal Symptom Rating Scale (GSRS) and the Visceral Sensitivity Index (VSI) were found to be the most appropriate and were administered to 393 adults with SM. The response rate was 78%. Of these, 147 (48%) reported having GI-problems due to SM and were thus included in this study. Reliability was assessed using Cronbach's alpha, whereas construct validity was examined through exploratory factor analysis. RESULTS: Internal consistency measured with Cronbach's alpha coefficient was overall good/excellent for the GSRS total scale (α = 0.88) and subscales (α = 0.72-0.84) and for the VSI (α = 0.93). The exploratory factor analysis revealed four factors for the GSRS (indigestion, diarrhea, constipation, pain/reflux) and two factors for the VSI (worries related to internal GI symptoms, external factors related to GI problems). CONCLUSIONS: Based on our results, we propose using the GSRS for measuring physical GI problems and the VSI for measuring psychosocial consequences and/or worries related to GI problems in the SM population. The instruments could be used to highlight GI problems in both clinical care and research. CLINICAL TRIAL.GOV REGISTRATION: Trial registration number: NCT06065007.