PB2708: SYMPTOM BURDEN AND ITS IMPACT ON DAILY LIFE IN PATIENTS WITH IDIOPATHIC MULTICENTRIC CASTLEMAN’S DISEASE (IMCD): AN EXPLORATORY ANALYSIS OF THE SURVEY’S INTERNAL CONSTRUCT VALIDITY

Topic: 36. Ethics and health economics Background: Idiopathic multicentric Castleman disease (iMCD) is a rare, life-threatening lymphoproliferative disorder characterized by systemic inflammatory symptoms, generalized lymphadenopathy, polyclonal lymphoproliferation, and multiple organ system dysfunction caused by a hyperinflammatory state. Patients experience high symptom burden and the mainstay of iMCD management is symptom control and preventing severe complications. Consequently, the quantification of symptoms and their impact on the daily lives could be a valuable clinical tool to monitor disease status, functional state, and response to treatment. Aims: Efforts to catalogue and understand how iMCD symptoms impact daily living from an international survey have been reported elsewhere. We conduct an exploratory analysis of the survey’s psychometric properties in terms of internal construct validity (i.e., assessing against factors in the same questionnaire with a similar construct) to assess its suitability for the generation of a Symptom Burden Scale. Methods: An online symptom burden survey specifically tailored to iMCD, was developed, based on literature and clinical expert advice. This survey was distributed within iMCD communities in Australia, Canada, the UK, and the US through the Castleman Disease Collaborative Network (CDCN). Ethics approval and patient consent were obtained. Following analysis of the responses relating to symptom burden, their severity (measured on a Likert scale: range 0-4), and the impact on their daily lives, exploratory analyses regarding the strength of the relationship between symptoms and their impact on daily activities were undertaken. Firstly, interviews with clinicians, patients and caregivers were conducted to understand whether response could be grouped as the same or related to one another. If items were related, the expected strength of the relationship and, for the clinical expert interviews only, the potential direction of relationship, were further explored. Secondly, hypotheses were generated a priori from these interviews and tested to establish the construct, convergent and discriminant validity of the survey. Spearman’s rank absolute correlation strength associated p-value, and Cohen’s d standardized effect size methods were utilized. Results: The survey was implemented from April–November 2020, with 51 respondents reporting confirmed iMCD diagnosis from a healthcare practitioner. Patients were predominantly female (56.9%), of mean age of 47.4 years (SD 11.9) and white (74.5%). The mean number of symptoms reported was 6.7 (SD: 5.2, Range: 0-22). 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 and the overall relationship with aspects of daily life. Although the results did support or negate all a priori hypotheses, a strong significant correlation between having a higher number of symptoms and greater adverse impact on daily life was identified. Summary/Conclusion: Despite sample size limitations for complex statistical analyses, 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 the assessment of patients’ symptom state and evaluation of response in daily practice or clinical research. Keywords: Castleman’s disease, Patient