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Keywords:

  • bladder;
  • epidemiology;
  • incidence;
  • interstitial cystitis;
  • Japan

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. Conflict of interest
  9. References

We estimated the incidence of admissions related to interstitial cystitis in Japan using a national administrative claims database, the Diagnosis Procedure Combination database, which included information for 53.6% of urological training hospitals certified by the Japanese Urological Association. “Admissions related to interstitial cystitis” was defined as those cases whose ICD-10 code for the main reason for admission was N301 (interstitial cystitis) between 2007 and 2009. Among 8.42 million inpatient cases, 784 female and 212 male patients with interstitial cystitis were identified. The ratio of females to males was 3.69 and the median age was 67 years (range 5–92 years). The admission incidence (per 100 000 person-years) in females and males was estimated to be 1.35 (95% confidence interval 1.25–1.46) and 0.37 (0.31–0.42), respectively. This incidence is low compared with other reports. Possible reasons for this finding include racial difference, clinical examination methods, lack of outpatient data and poor health-care coverage of interstitial cystitis.


Abbreviations & Acronyms
IC =

Interstitial cystitis

DPC =

Diagnosis Procedure Combination

JUA =

Japanese Urological Association

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. Conflict of interest
  9. References

Interstitial cystitis (IC) is a chronic disease of the urinary bladder characterized by lower urinary tract symptoms, such as urinary frequency, bladder hypersensitivity and/or bladder pain and resultant serious impairment of quality of life.1

Although the National Institute of Arthritis, Diabetes, Digestive and Kidney Disease proposed the diagnostic criteria of IC for research use in 1988,2 it has not been widely used in the clinical setting because of its strictness and complicacy. To promote research activity and medical care of IC in Japan and East Asia, the Clinical Guidelines for IC were established by the Society of Interstitial Cystitis of Japan in 2007.1

Estimation of the incidence or prevalence of IC in the general population is difficult because of its rarity. Although several articles estimating the incidence or prevalence of IC have been published,3–10 many of them were based on restricted sample populations (i.e. office visitors and nurses’ cohort) or scoring questionnaire research and few focused on male patients. To our knowledge, just three articles from the USA have been published to estimate the male and female incidence or prevalence of IC in the general population based on clinical diagnosis.5,9,10

The present study evaluated the incidence of admissions related to IC in both the male and female general population in Japan, using the Diagnosis Procedure Combination (DPC) database, which is a nationwide administrative database.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. Conflict of interest
  9. References

The DPC database

The DPC database is a case-mix inpatient claims database.11–14 During our study period of 2007–2009, the database contains annually approximately 2.6 million inpatient cases from approximately 850 hospitals from July to December (6 months per each year), which represents approximately 44% of all acute care inpatient hospitalizations in Japan. Given the anonymous nature of the data collection process, informed consent was not required. Study approval was obtained from the Institutional Review Board in the University of Occupational and Environmental Health.

Japanese Urological Association-certified hospitals

The Japanese Urological Association (JUA) is the professional urological association in Japan. The JUA certifies urological specialists and hospitals where the teaching system is ensured (JUA-certified hospitals).

Study samples

In the DPC database, one disease should be assigned to “the main reason for admission” category. We defined “admissions related to IC” as those cases whose ICD-10 code for the main reason for admission was N301 (IC), and we identified them from the DPC database in 2007–2009.

Estimation of prevalence of IC

We estimated the incidence of admissions related to IC based on stratified hospital bed volume. First, we collected the number of beds in all JUA-certified hospitals and hospitals that had joined the DPC database. Hospitals were stratified with bed volume categories. The estimated annual number of IC cases (Yi) and the 95% confidence intervals (CI) were calculated with the following equation using Wald confidence intervals for the population proportion:13

  • image

where Ni is the number of beds in all JUA-certified hospitals, ni is the number of beds in JUA-certified hospitals that joined the DPC database, pi =Xi/(ni × 1.5) (Xi is the observed number of IC cases in JUA-certified hospitals that joined the DPC database between July and December, 2007–2009), and Z = 1.96.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. Conflict of interest
  9. References

Among 8.42 million inpatients in the study population, we identified 996 admissions related to IC (Table 1). The ratio of females to males was 3.69 and the median age was 67 years (range 5–92 years). Almost all patients (95.3%) were hospitalized in JUA-certified hospitals. A vast majority of patients underwent cystoscopic intervention. Although they were minor, cystectomies and augmentation cystoplasties were also selected for therapy.

Table 1.  Distribution of male and female interstitial cystitis patients from the Diagnosis Procedure Combination database
TotalMalesFemales
212 (100.0%)784 (100.0%)
  1. IQR, interquartile range; JUA, Japanese Urological Association.

Age (years)  
 ≤194 (1.9%)9 (1.1%)
 20–295 (2.4%)29 (3.7%)
 30–397 (3.3%)42 (5.4%)
 40–499 (4.2%)47 (6.0%)
 50–5926 (12.3%)95 (12.1%)
 60–6965 (30.7%)215 (27.4%)
 70–7975 (35.4%)268 (34.2%)
 80–8920 (9.4%)76 (9.7%)
 ≥901 (0.5%)3 (0.4%)
 Median (IQR)67 (59–76)67 (57–74)
Year  
 200780 (37.7%)263 (33.5%)
 200858 (27.4%)242 (30.9%)
 200974 (34.9%)279 (35.6%)
JUA hospital200 (94.3%)750 (95.7%)
Intervention  
 Cystoscopic interventions including hydrodistension176 (83.0%)706 (90.1%)
 Augmentation cystoplasty2 (0.9%)2 (0.3%)
 Simple cystectomy1 (0.5%)2 (0.3%)
 Implantation of spinal cord stimulation apparatus3 (1.4%)1 (0.1%)
 Missing or others30 (14.2%)73 (9.2%)

Table 2 shows the distribution of hospitals and IC cases stratified with bed volume categories. Overall, the DPC database covered 53.6% of JUA-certified hospitals and 63.4% of those beds. The estimated annual number of IC cases per year was 886 in females and 231 in males. According to the Population Census Data, the population of Japan in 2008 was approximately 65.44 million females and 62.25 million males; therefore, the incidence of admission related to IC (per 100 000 person-years) in females and males was estimated as 1.35 (95% CI 1.25–1.46) and 0.37 (0.31–0.42), respectively.

Table 2.  Estimated incidence of admissions related to interstitial cystitis in Japan
Bed volumeJUA-certified hospitals (2007–2009)JUA-certified hospitals that joined the DPC database (2007–2009)No. IC patients in the DPC database for 1.5 years [Xi]Estimated annual no. IC patients (95% confidence interval) [Yi]
nNo. of beds [Ni]nNo. of beds [ni]MalesFemalesMalesFemales
  • Data were collected from six months (July to December) of each 3 years (2007–2009).

  • Yi/Ni = pi ± 1.96 × σi, where pi = Xi/(ni × 1.5), σi2 = pi (1 – pi)/(ni × 1.5).

  • ΣYi = Σ (Ni × pi) ± 1.96 × (ΣNi × σi2)0.5. DPC, Diagnosis Procedure Combination; IC, interstitial cystitis; JUA, Japanese Urological Association.

≥8006260 7685080.6%50 27882.7%4218334 (24–44)147 (126–169)
600–79910772 4378074.8%54 39475.1%3111528 (18–37)102 (83–121)
400–599336161 95122466.7%109 83467.8%4116540 (28–53)162 (137–187)
200–399512153 26526952.5%81 48053.2%94273118 (94–142)342 (302–383)
≤19923130 4864619.9%740624.3%44811 (0–22)132 (95–169)
Total1248478 90766953.6%303 39263.4%212784231 (198–263)886 (819–952)
Total population in 2008 (100 000 persons)622.5654.4
Incidence (per 100 000 person-years)0.37 (0.31–0.42)1.35 (1.25–1.46)

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. Conflict of interest
  9. References

In the present study, we used a large administrative database and identified IC with a registered ICD-10 code. A similar method was used in two previous studies using Kaiser Permanente Northwest, a health maintenance organization in Portland, Oregon, USA. Clemens et al.9 reported that “the prevalence” of IC during 1998–2002 was 197 and 41 per 100 000 in females and males, respectively, when IC was defined as the ICD-9 code 595.1, and Patel et al.5 reported that “the incidence” of IC during 2002–2005 was 15 per 100 000 in females (no male patients were identified). Therefore, there is a 10-fold discrepancy between our results and those of Patel et al.

The incidence of IC varies widely, even though IC is diagnosed by clinical examination. Robert et al. analyzed Olmsted Country cohort data (1976–1996) and reported that the incidence of IC diagnosed through cystoscopic intervention was 1.6 and 0.6 per 100 000 in females and males, respectively.10 Leppilahti et al. carried out a clinical examination in Finnish people who scored high points in the O’Leary-Sant IC symptom and problem index (OLS) questionnaire, and concluded that the prevalence of probable IC in women was 230 per 100 000 and that of possible/probable IC was 530 per 100 000.8

Recently, several questionnaires measuring the severity of IC, such as the OLS, have been developed. According to some OLS-based surveys, the prevalence of possible IC or painful bladder syndrome (per 100 000 females) is estimated to be 575 in the USA,7 306 in Austria,6 265 in Japan4 and 261 in Korea.3 These data suggest that there is some racial discrepancy between Asia, European countries and the USA, but the differences seem not so largely radical to solely explain the 10-fold gap. This implies that several IC patients remain undiagnosed and untreated in Japan.

Although the Clinical Guidelines for IC were released in January 2007 in Japan to promote research and clinical activity for IC,1 the number of patients did not increase (Table 1). We consider there to be two possible reasons for this finding. First, racial variants and differences in database background could be attributed to our low IC incidence. In particular, the DPC database did not contain outpatient cases and our result of “incidence of admission related to IC” did not directly represent overall IC incidence. A previous report described that hydrodistension can be safely carried out under local anesthesia without hospitalization.15 Second, Japanese national health-care insurance does not currently cover hydrodistension. Special approval from authorities is required to carry out hydrodistension (this restriction was lifted in April 2010).

Finally, we showed that the DPC database is highly represented in the urological field. The database coverage rate is approximately 35% of whole acute care beds,13 but by restriction to JUA-certified hospitals, it increased to 53.6%. This high coverage enables accurate clinical assessment.

There are several limitations in the present study. First, the definition of IC was only based on an ICD-10 code in the administrative database. Neither chart reviews nor scoring questionnaires were available in the database. Second, because the present study was based on administrative claims data, the validity and reliability of the written diagnoses were limited, resulting in underestimation.

The incidence of admission related to IC from the DPC database (per 100 000 person-years) is estimated as 1.35 in females and 0.37 in males. Possible reasons for this low incidence include racial difference, clinical examination methods, lack of outpatient data and poor health-care coverage for IC.

Acknowledgment

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. Conflict of interest
  9. References

The present study was funded by a Grant-in-Aid for Research on Policy Planning and Evaluation from the Ministry of Health, Labour and Welfare, Japan (Grant number: H19-Policy-001).

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. Conflict of interest
  9. References
  • 1
    Homma Y, Ueda T, Tomoe H et al. Clinical guidelines for interstitial cystitis and hypersensitive bladder syndrome. Int. J. Urol. 2009; 16: 597615.
  • 2
    Hanno PM, Landis JR, Matthews-Cook Y, Kusek J, Nyberg L Jr. The diagnosis of interstitial cystitis revisited: lessons learned from the National Institutes of Health Interstitial Cystitis Database study. J. Urol. 1999; 161: 5537.
  • 3
    Choe JH, Son H, Song YS, Kim JC, Lee JZ, Lee KS. Prevalence of painful bladder syndrome/interstitial cystitis-like symptoms in women: a population-based study in Korea. World J. Urol. 2011; 29: 1038.
  • 4
    Inoue Y, Mita K, Kakehashi M, Kato M, Usui T. Prevalence of painful bladder syndrome (PBS) symptoms in adult women in the general population in Japan. Neurourol. Urodyn. 2009; 28: 21418.
  • 5
    Patel R, Calhoun EA, Meenan RT, O’Keeffe Rosetti MC, Kimes T, Clemens JQ. Incidence and clinical characteristics of interstitial cystitis in the community. Int. Urogynecol. J. Pelvic Floor Dysfunct. 2008; 19: 10936.
  • 6
    Temml C, Wehrberger C, Riedl C, Ponholzer A, Marszalek M, Madersbacher S. Prevalence and correlates for interstitial cystitis symptoms in women participating in a health screening project. Eur. Urol. 2007; 51: 8038.
  • 7
    Rosenberg MT, Hazzard M. Prevalence of interstitial cystitis symptoms in women: a population based study in the primary care office. J. Urol. 2005; 174: 22314.
  • 8
    Leppilahti M, Sairanen J, Tammela TL, Aaltomaa S, Lehtoranta K, Auvinen A. Prevalence of clinically confirmed interstitial cystitis in women: a population based study in Finland. J. Urol. 2005; 174: 5813.
  • 9
    Clemens JQ, Meenan RT, O’Keeffe Rosetti MC, Gao SY, Calhoun EA. Prevalence and incidence of interstitial cystitis in a managed care population. J. Urol. 2005; 173: 98102.
  • 10
    Roberts RO, Bergstralh EJ, Bass SE, Lightner DJ, Lieber MM, Jacobsen SJ. Incidence of physician-diagnosed interstitial cystitis in Olmsted County: a community-based study. BJU Int. 2003; 91: 1815.
  • 11
    Sugihara T, Yasunaga H, Horiguchi H et al. Impact of hospital volume and laser use on postoperative complications and in-hospital mortality in cases of benign prostate hyperplasia. J. Urol. 2011; 185: 224853.
  • 12
    Yasunaga H, Yanaihara H, Fuji K, Horiguchi H, Hashimoto H, Matsuda S. Impact of hospital volume on postoperative complications and in-hospital mortality after renal surgery: data from the Japanese Diagnosis Procedure Combination Database. Urology 2010; 76: 54852.
  • 13
    Sako A, Yasunaga H, Horiguchi H, Hashimoto H, Masaki N, Matsuda S. Acute hepatitis B in Japan: incidence, clinical practices and health policy. Hepatol. Res. 2011; 41: 3945.
  • 14
    Sugihara T, Yasunaga H, Horiguchi H, Nishimatsu H, Matsuda S, Homma Y. Incidence and clinical features of priapism in Japan: 46 cases from the Japanese diagnosis procedure combination database 2006–2008. Int. J. Impot. Res. 2011; 23: 7680.
  • 15
    Aihara K, Hirayama A, Tanaka N, Fujimoto K, Yoshida K, Hirao Y. Hydrodistension under local anesthesia for patients with suspected painful bladder syndrome/interstitial cystitis: safety, diagnostic potential and therapeutic efficacy. Int. J. Urol. 2009; 16: 94752.