Background: Severe pelvic pain is the commonest and most troublesome symptom associated with endometriosis, and typically coincides with the menstrual, premenstrual and periovulatory phases.  These are frequently accompanied by exquisite tenderness of affected pelvic structures, notably during deep penetration at sexual intercourse or during bowel movement.  Painful abdominal bloating is common premenstrually and is one of a range of gastrointestinal symptoms.

Methodology:  We have carried out a range of laboratory studies on affected pelvic tissues obtained from women with and without different types of endometriosis, mainly with the use of immuno-histochemical markers for specific nerve fibres, neurotrophins and their receptors.  We have studied changes in the sensory thresholds for peripheral perception of pain in women with and without endometriosis using Quantitative Sensory Testing.

Results and Conclusions: In endometriosis, unmyelinated sensory, sympathetic and parasympathetic nerve fibres are present in much greater density in uterine tissues (especially endometrium) and endometriotic lesions than in normal reproductive tract tissues, and express a wide range of neuronal markers.  It is probable that these sensory nerve fibres have primary roles in the generation of pelvic pain.  Preliminary sensory testing suggests that women with endometriosis have lowered thresholds for the perception of pain associated with pressure, heat and cold.  These observations indicate that pelvic innervation is disturbed in women with endometriosis, that endometriotic nerve fibres may interact with the enteric nerve plexus in lesions involving bowel, and that peripheral pain perception thresholds may be lowered in many endometriosis sufferers.