OBJECTIVES: Idiopathic multicentric Castleman’s disease (iMCD) is a rare lymphoproliferative disorder driven by proinflammatory hypercytokinemia. Patient perspective of the burden and associated symptoms of iMCD on their daily life have not been previously studied. We developed a bespoke international survey to elicit the burden of iMCD and explored its psychometric properties in relation to construct validity.

METHODS: We generated hypotheses based on expert opinion (one clinician, one patient, and one caregiver) via interviews to understand whether specific questions and response options within the survey could be: grouped together as the same; related to one another; if items are related, the expected strength of the relationship and, for the clinical expert only, the potential direction of relationship. We used Spearman’s rank absolute correlation strength and associated p-value, and Cohen’s d standardized effect size methods.

RESULTS: Overall, 57 patients with iMCD completed the survey between April–November 2021. Patients had a mean number of 7 symptoms (range: 0 to 22 symptoms). Three a priori hypothesis sets were generated: 1. How specific symptoms relate to each other; 2. Number of symptoms and their relationship with aspects of daily life; and 3. Receiving treatment or not, and the overall relationship with aspects of daily life. Although the results did not enable support or refutation of all a priori hypotheses, we found a strong significant correlation between having a higher number of symptoms and greater adverse impact on daily life.

CONCLUSIONS: This exploratory analysis provides confidence in the internal construct validity of the survey. It supports use of this disease burden questionnaire as a tool for assessing disease severity, aiding treatment decision, and evaluating responses in daily practice and clinical research.