The 'evil twin syndrome' in chronic pelvic pain: a systematic review of prevalence studies of bladder pain syndrome and endometriosis

BACKGROUND: Chronic pelvic pain (CPP), a common gynaecological presentation, may be due to bladder pain syndrome (BPS) or the co-existence of BPS and endometriosis, known as the 'evil twins syndrome'. OBJECTIVES: To estimate the prevalence of BPS and the co-existence of BPS and endometriosis in women with CPP. DATA SOURCES: We searched until March 2012: The Cochrane Library, DARE (1997-2012), EMBASE (1980-2012), Medline (1950-2012), PSYCHINFO (1806-2012), Web of knowledge (1900-2012), LILACS (1982-2012) and SIGLE (1990-2012) with no language restrictions. We manually searched through bibliographies and conference proceedings of the International Continence Society. STUDY SELECTION: Observational studies of women suffering from CPP, who were not pregnant or suffering from cancer, who underwent a laparoscopy and cystoscopy to investigate their symptoms. Study selection, data extraction and quality assessment was performed independently by two reviewers. Statistical analysis was performed to estimate prevalence and confidence intervals (CI). RESULTS: Nine studies were included with 1016 patients with CPP. Study quality and diagnostic assessment varied. The mean prevalence of BPS was 61% (range 11-97%, CI 58-64%, I(2) = 98%). The mean prevalence of endometriosis was 70% (range 28-93%, CI 67-73%, I(2) = 93%) and co-existing BPS and endometriosis was 48% (range 16-78%, CI 44-51%, I(2) = 96%). CONCLUSION: Almost two thirds of women presenting with CPP have BPS. Large variations in prevalence may be due to variable study selection and quality. Clinicians need to actively investigate patients for BPS, a condition that appears to co-exist with endometriosis.