Pelvic pain is the most common presenting symptom of endometriosis. Pain thresholds appear to be lowered in women suffering painful endometriosis. Nerve conduction studies to elucidate contributors to this phenomenon have often investigated large, myelinated peripheral nerves and a loss of function. Recently, increased sensory innervation has been observed in peritoneal lesions, myometrium and endometrium of women with endometriosis. Therefore, exploring how sensory inputs contribute to endometriosis-associated, pelvic pain may accentuate hitherto unknown aspects of disease progression.
This study aimed to examine afferent (sensory) pathways. In the female pelvis, visceral nociceptive events may be altered in endometriosis giving rise to central sensitization, concomitant peripheral sensitization and central amplification. Distorted pain perception may be the result.
We utilised Quantitative Sensory Testing (QST): the application of a standardised battery of potentially noxious stimuli to endometriosis subjects, with considerable pain, and to pain-free, aged-matched controls, as outlined by the German Research Network for the study of Neuropathic Pain (DFNS). QST assesses primary afferents through self-reported, detection- and pain-thresholds of applied stimuli. Stimuli are grouped as thermal, mechanical, vibratory and pressure. Sites included the (control) dorsal hand and (test) lower, midline abdominal (T11 dermatome) and lumbosacral spine (L4-S1).
Currently, 5 endometriosis subjects have been tested. Preliminary data point to heightened sensitivity, or a lowered threshold, to the applied stimuli.
Chronic pelvic pain is a common, debilitating symptom of endometriosis. The presence of endometriosis appears to impact the density of sensory neurons and their encoding and transmission of visceral nociceptive events. Convergence of nerve fibres near the spinal column allows for somatic stimulation to identify pathways of sensory visceral input and resultant alterations to central processing. Revealing the contributors to endometriosis-associated pain may improve understanding of the disease and extend management options.