Primary Afferent Nociceptors and Visceral Pain

Abstract

Patients with chronic pelvic pain frequently have pain from several pelvic organs. The most common diagnoses include endometriosis, interstitial cystitis, irritable bowel disease, pelvic floor tension myalgia, vulvar vestibulitis, and vulvodynia. Frequently, pain does not correlate with pathologic findings at the time of laparoscopy in the case of endometriosis, while vulvodynia, irritable bowel syndrome and pelvic floor tension myalgia and neuropathy may have no clearly demonstrable pathologic tissue changes. Most diagnoses associated with chronic pelvic pain have a high rate of recurrence and all are considered to be chronic conditions with a relapsing course. Endometriosis is a complex, poorly understood chronic illness of women in their reproductive age and pain is the major concern of women with this disease. Despite a successful reduction of pain using during the novel treatments pain returns in up to 75% of treated women. Pain is strongly associated with this disease and the lack of awareness to its pathology is further illustrated by the fact that the average time duration between the onset of pain and the diagnosis of endometriosis is 3 to 11 years despite the fact that 25-30% of women with chronic pelvic pain suffer from this disease. In women with endometriosis (mainly of reproductive age) alterations in the limbic and sympathetic nervous system and hypothalamic-pituitary-adrenal axis mediate a cycle of hypervigilance for pain sensations from pelvic organs, which can lead to descending induction of pathologic changes in pelvic organs. Chronic pelvic pain patients frequently have multiple diagnoses. Vicero-somatic and viscero-viseral hyperalgesia and allodynia result in the spread of a perception of pain from an initial site to adjacent areas. Chronic pelvic pain patients may initially have only one pain source in the pelvis, such as the uterus in dysmenorrhea or endometriosis implants, but a multitude of mechanisms involving the peripheral and central nervous system can lead to the development of painful sensations from other adjacent organs. Often the etiology of visceral pain is not clear, as there are many symptoms of the reproductive system, gastrointestinal and urinary tracts, musculoskeletal, neurological and psychological systems that often co-occur in the same patient. The variation of pain symptoms and pain perception and behavioral responses to pain in these patients is poorly understood. The treating clinician is often tempted to take a unidimensional approach and focus on one organ system and ignore the psychological and behavioral manifestations of the chronic pain.