Pain evoked by distension of the uterine cervix in women with dysmenorrhea: evidence for central sensitization

Objective. To study sensitization in women with dysmenorrhea using a standardized experimental model. Women with dysmenorrhea experience intense visceral pain during menstruation. The dysmenorrhea pain mechanisms are not known but sensitization may play a role. Design. Prospective experimental study. Sample. Ten women with dysmenorrhea and 10 control women having uterine cervical distensions in the mid-follicular period (days 6-10). Setting. University clinic. Method. Cervical distension was delivered as three phasic stimuli with 1 min between distensions and as a prolonged (1 min) distension. Main outcome measure. Sensory intensity rated on a continuous visual analog scale. Results. Distension-induced pain was described as dull and aching and referred to the pelvis, lower back and lower abdomen. Larger evoked referred pain areas were present in women with dysmenorrhea compared with control women (p < 0.05). The pain threshold to the first stimulus was significantly higher in patients than controls (p < 0.04), but decreased significantly with repeated distensions (p < 0.01). For the prolonged distension the pain rating increased significantly (p < 0.008) in women with dysmenorrhea, but decreased (p < 0.02) in control women. Conclusions. Pain sensitization (temporal summation, i.e. increase in pain during prolonged stimulation, and facilitation of referred pain areas as an indicator of central nervous system changes) is present in women with dysmenorrhea. The study provided new information on a poorly understood yet widespread condition and a basis for clinical studies to develop a biomarker tests for objective assessment of dysmenorrhea.