AIMS: To assess the distinct histopathological characteristics and their clinical significance between non-Hunner-type and Hunner-type interstitial cystitis (IC)/bladder pain syndrome (BPS). METHODS AND RESULTS: We prospectively enrolled and classified IC/BPS patients, on the basis of cystoscopic findings, as having non-Hunner-type IC and Hunner-type IC. Specimens obtained from the posterior wall in non-Hunner-type IC cases during hydrodistension or from Hunner/non-Hunner lesions in Hunner-type IC cases during transurethral resection were evaluated. Stress urinary incontinence patients with microscopic haematuria were selected as controls. Biopsy specimens were obtained from 15 non-Hunner-type IC, 15 Hunner-type IC and 5 non-IC patients. Severe and moderate fibrosis was more frequently observed in non-Hunner-type IC than in Hunner-type IC and non-IC cases. However, severe and moderate inflammation was more frequently observed in Hunner-type IC than in non-Hunner-type IC cases. The remnant urothelium was significantly decreased in Hunner-type IC cases as compared with non-Hunner-type IC and non-IC cases (P < 0.05), and non-Hunner-type IC cases showed a higher number of mast cells than Hunner-type IC and non-IC cases (P = 0.035). Accordingly, several fibrosis-promoting genes were highly expressed in bladder tissues of non-Hunner-type IC, as compared with Hunner-type IC. Patients with severe fibrosis showed significantly higher urinary frequency and smaller bladder capacity than those with moderate and mild fibrosis (all P < 0.05). CONCLUSIONS: Non-Hunner-type IC is characterized by severe fibrosis and increased mast cell infiltration, whereas Hunner-type IC is characterized by severe inflammation and urothelial denudation in the entire bladder. Fibrosis in the bladder of IC/BPS patients was correlated with increased urinary frequency and decreased bladder capacity.
