Classical conditioning and expectancy in placebo hypoalgesia: a randomized controlled study in patients with atopic dermatitis and persons with healthy skin

Provoked vestibulodynia is a common cause of superficial dyspareunia in young women. Recent evidence has pointed out the importance of studying endogenous pain modulation in these women. An impairment of diffuse noxious inhibitory controls (DNIC) has been suggested in chronic pain conditions with a female predominance such as fibromyalgia and temporomandibular disorder. Our aim was to examine whether patients with provoked vestibulodynia and healthy women with or without combined oral contraceptives (COC) display a DNIC response to cold noxious stimulation. Twenty patients with provoked vestibulodynia not using COC, 20 healthy women on COC and 20 healthy women without COC were included and tested days 7-11 of their menstrual cycle. Pressure pain thresholds (PPTs) and pain ratings using VAS were measured on the arm and leg before and during a cold pressor test. A socio-medical questionnaire, the Hospital and Anxiety Depression Scale and the Short Form-36 were completed. The majority of the subjects in all three study groups significantly increased their PPTs during cold noxious stimulation indicating a DNIC response. The patients displayed lower PPTs compared to the healthy women. Depression, anxiety and bodily pain were more often reported by the patients. No differences related to the intake of COC were observed between the healthy women. In conclusion, women with provoked vestibulodynia as well as healthy women irrespective of COC status display a DNIC response indicating an endogenous pain inhibition. However, the results imply a systemic hypersensitivity in women with vestibulodynia with low general pain thresholds as compared to healthy women.