INTERSTITIAL cystitis/bladder pain syndrome (IC/BPS) predominantly affects women and presents with severe lower urinary tract symptoms and debilitating bladder pain, significantly impairing quality of life. Despite normal blood tests, urinalysis, and imaging findings, IC/BPS remains poorly understood due to its small patient population and unclear aetiology. Recent research has identified two distinct clinical subtypes: IC with Hunner lesions and BPS without these lesions. These classifications, advocated by recent guidelines, offer insight into differing clinical presentations.
IC, associated with Hunner lesions, shows signs of immunogenic inflammation, including lympho-plasma cell infiltration and epithelial damage. Genetic studies have linked IC to HLA-DQb1, supporting an autoimmune component. In contrast, BPS lacks inflammatory changes and is linked to urothelial dysfunction and neurophysiological abnormalities, often accompanied by somatic and psychological symptoms. These differences necessitate separate clinical analyses, which have been scarce due to the previous practice of grouping IC and BPS together in studies.
A comprehensive study in Japan, involving 529 patients, separated IC and BPS cases for analysis. It revealed that IC patients were older, predominantly female, and exhibited more severe symptoms, including higher pain levels, frequent urination, and reduced bladder capacity. Notably, the study identified a higher proportion of IC (66.5%) compared to reports from other countries, likely due to rigorous diagnostic practices, including cystoscopy, employed by the participating tertiary care hospitals.
The study also noted that IC patients had a higher prevalence of autoimmune diseases and more severe quality of life impairment. Nighttime urination frequency and reduced bladder capacity were significantly worse in IC, potentially due to bladder fibrosis and inflammation. Pain predictors in IC included reduced voiding volume and the extent of Hunner lesions, while pain in BPS may relate to nerve growth factor expression and systemic somatoform disorders.
Although limitations such as inconsistencies in diagnostic practices and retrospective data exist, this large-scale study underscores critical differences between IC and BPS, enhancing understanding of their distinct aetiologies and informing tailored management strategies.
Katie Wright, EMJ
Reference
Niimi A et al. Clinical manifestations of interstitial cystitis and bladder pain syndrome: Analysis of a patient registry in Japan. Int J Urol. 2025;32(1):103-9.
