Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic pain syndrome perceived to be related to the urinary bladder. However, it is associated with multifactorial etiology, including inflammatory processes, infections, autoimmunity, local neuronal dysfunction or mucosal abnormalities. IC/BPS is part of systemic disorders or a member of family of hypersensitivity disorders that affects the bladder and other somatic/visceral organs [1]. Our study aimed to test the hypothesis that IC/BPS patients are associated with subsequent increased risks of out-patient visits and hospitalizations, in addition to urology and gynecology.

Study design: We identified IC/BPS subjects from national health registry database, and 1 to 1 age-matched controls. Then, we followed and evaluate the subsequent risks of out-patient visits and hospitalizations, among IC/BPS subjects, as compared with non-IC/BPS controls, and the age effect on the risks. 

Materials and methods: This was a nationwide population-based cohort study from the national health registry database. The diagnostic code of IC/BPS used in the registry database are based on the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9 CM) codes (595.1) at least three out-patient service claims and pre-audit for hyaluronate irrigation during 2002-2008, (n=2,990). To restrict our study group in more well-defined subjects, we recruited only IC/BPS patients who received bladder instillation of sodium hyaluronate, in which, the prescription of sodium hyaluronate requires a strict pre-review. Its provision including: the presence of glomerulation or Hunner’s lesions under cystoscopy after hydrodistention test, voiding diary, negative urine cytology and urine analysis [2]. 
    All recruited cases were monitored for OPD visits and hospitalizations (excluding IC/BPS-related health-care services) for 2 years following the index date, except those who expired during the follow-up period. Subsequent health-care services, including all-cause and specialty-specific hospitalizations, were classified according to medical specialty and age group (<40, 40 - 60, ≥60 years of age).

IC/BPS patients have more overall OPD visits, overall adjusted incidence rate ratio (IRR) 1.64, (95%CI 1.62-1.66). As for specialty, IRRs were higher in psychiatry 2.75, Chinese medicine 2.01, and emergency medicine 2.00, besides urology and gynecology. The IRRs decreased as age advanced (2.01, 1.71, and 1.44, for <40, 40 - 60, ≥60 years of age, respectively), except for gynecology (2.42, 2.52, and 2.81). 
   A similar phenomenon happens in hospitalization with IRR 1.694, (95%CI 1.58-1.80). As for specialty, IRRs were higher in psychiatry 2.66, colorectal 1.90, and internal medicine 1.77, and neuro surgery 1.68, besides urology and gynecology. The IRRs decreased as age advanced (2.25, 1.68, and 1.59, <40, 40 - 60, ≥60 years of age respectively), except for gynecology (1.45, 2.29, and 4.70).

To our best knowledge, this is the first large-scale nationwide study to estimate the risk about outpatient visit and hospitalization risk between patients with and without IC/BPS. This population‐based matched‐cohort study using nationwide insurance database indicated IC/BPS individuals have more outpatient visit and hospitalization. The increasing risk not only showed in urology and gynecology department, but also all other clinical departments. Our study indicates the impacts of healthcare burden in broad spectrum about IC/PBS patients. 
Possible explanations were firstly, IC/BPS patients may have lower threshold of medical healthcare visits [3]. Secondly, IC/BPS patients may have some co-existing medical disease. Thirdly, IC/BPS may comprise multiple systemic dysregulation, instead of only local bladder-urethra disease only.

In this study, we found that patients with IC/PBS have significantly higher number of outpatient visits and hospitalizations, compared to non-IC/PBS controls, not only in urology and gynecology department, but also in nearly all specialties. This study also provides a broader understanding of IC/PBS within multiple and overlapping systems. These findings and explanations are emphasized that patient with IC/PBS should be paid more attention due to systemic complex disease and higher medical service. Thus, our findings broaden our understanding about IC/BPS, from organ-centered to multiple system concepts.

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