Central sensitization in urogynecological chronic pelvic pain: a systematic literature review.

BACKGROUND: Chronic pelvic pain (CPP) is a complex pain syndrome. Since its pathogenesis is still poorly understood and structural alterations in pain related brain regions may be present, there is a greater acceptance that sensitization of the central nervous system (CNS) plays an important role in the development and maintenance of chronicity. OBJECTIVE: The purpose of this study is to systematically review the scientific evidence regarding central sensitization (CS) in female patients with urogynecological CPP. STUDY DESIGN: Systematic review of the literature. METHODS: A systematic literature search was conducted in PubMed and Web of Science using different keyword combinations related to urogynecological CPP and central sensitization. Full text clinical reports addressing CS in adult women with urogynecological CPP were included and assessed for methodological quality by 2 independent reviewers. RESULTS: After screening for the eligibility, a total of 29 full-text articles with low to good methodological quality were retained. All studies were observational, 27 of which were case-control and 2 of which were cohorts. Sensitivity of the CNS was investigated by using a variety of methods. Although different central mechanisms seem to be involved in pain processing, the present evidence suggests hyperexcitability of the CNS in patients with urogynecological CPP. Altered brain morphology and function, generalized hyperalgesia to different type of stimuli, overactive bottom-up nociceptive mechanisms, and autonomic dysregulation were established in patients with urogynecological CPP. Nevertheless, diffuse noxious inhibitory control seemed normal, and therefore the contribution of an impaired endogenous pain inhibition mechanism to CPP requires further study. The same goes for the contribution of psychological factors. LIMITATIONS: The level of evidence of retained studies is low due to the observational study designs and a wide range of diagnoses and assessment methods. CONCLUSION: Although the majority of the literature provides evidence for the presence of CS in urogynecological CPP with changes in brain morphology/function and sensory function, it is unclear whether these changes in central pain processing are secondary or primary to CPP, especially since evidence regarding the function of endogenous pain inhibition and the role of psychosocial pain facilitation is scarce. Further studies with good methodological quality are needed in order to clarify exact mechanisms.