Factor analysis identifies three separate symptom clusters in idiopathic pulmonary fibrosis

Background: Idiopathic pulmonary fibrosis (IPF) is a severe and progressive lung disease with a poor prognosis. Patients with IPF suffer from a high symptom burden, which impairs their health-related quality of life (HRQoL). Lack of research on IPF symptoms and their clustering, however, makes symptom-centred care challenging. Methods: We sent two questionnaires, RAND 36-Item Health Survey and Edmonton Symptom Assessment System, to 300 patients from the FinnishIPF registry. Of the 300 patients, 245 (82%) responded. We performed an exploratory factor analysis on the results to search for potential clustering of symptoms into factors. Results: We found three distinct symptom factors: the emotional factor (including depression, anxiety, insomnia, loss of appetite and nausea), the pain factor (pain at rest or in movement) and the respiratory symptoms factor (shortness of breath, cough, tiredness and loss of wellbeing). Correlation was strong within the factors (rho(tau) 0.78-0.85) and also evident between them. The factors correlated with the different dimensions of HRQoL: the emotional factor with mental health (correlation coefficient=-0.69) and vitality (-0.63), the pain factor with bodily pain (-0.72) and the respiratory symptoms factor with vitality (-0.69), general health (-0.64) and physical functioning (-0.62). Conclusion: We found three distinct symptom factors in IPF, of which respiratory and emotional factors showed the strongest association with decreasing HRQoL. Routine assessment of IPF patients' respiratory symptoms, mental health and pain are important as these may be linked with other symptoms and significantly impair the patient's HRQoL.