Spanish adaptation and validation of Mishel’s Uncertainty in Illness Scale (MUIS-A) in cancer patients

PURPOSE: Uncertainty is a major factor affecting cancer patients throughout all stages of the disease. Given its impact, this study aimed to adapt Mishel's Uncertainty in Illness Scale (MUIS-A) into Spanish for cancer patients in Spain and to analyze the relationship between uncertainty and selected clinical and psychosocial variables. METHODS: A descriptive cross-sectional transcultural adaptation and psychometric validation study was conducted using a prospective convenience sample of 174 cancer patients undergoing chemotherapy and/or immunotherapy. Uncertainty, socio-family support, dependence in activities of daily living, and functional status were assessed using validated questionnaires. Principal Component Analysis (PCA) and correlational analyses were performed to examine the factorial structure and associations among variables. RESULTS: Principal Component Analysis (PCA) supported the presence of the four dimensions of the original scale in the Spanish version. The 33-item scale showed good internal consistency (Cronbach's alpha = 0.794) and an initial explained variance of 39.26%. After an iterative item reduction process to improve factor loadings, a 26-item version was obtained, maintaining the four-factor structure, acceptable reliability (Cronbach's alpha = 0.787), and increasing the total explained variance to 44.6%. The mean uncertainty score was 73.15 ± 14.41. Most patients reported adequate social support and were independent in basic activities of daily living. A significant negative association was found between social support and uncertainty (r = - 0.315, p < 0.001). Additionally, a significant negative association was observed between uncertainty and the number of disease-related hospital admissions (Z = - 2.775, p < 0.005). CONCLUSIONS: The Spanish transcultural adaptation of Mishel's Uncertainty in Illness Scale is a reliable and valid tool for assessing uncertainty in cancer patients in Spain. Uncertainty was present in all participants and was significantly associated with socio-family support and disease-related hospital admissions. Its clinical application provides a practical resource for oncology nurses to facilitate psychosocial screening and tailor specific communication strategies.