Quantitative Sensory Testing in Vulvodynia Patients and Increased Peripheral Pressure Pain Sensitivity

Abstract

To determine if vulvodynia is more pronounced in patients with a low overall sensitivity to pain, the authors used objective measures to quantify generalized pressure pain sensitivity and local vulvar pressure pain sensitivity. A standard dolorimeter was used to measure pressure pain sensitivity at bilateral sites over the deltoid muscle, 5 cm below the kneecap on the shin, and on the thumbnail. Similarly, a vulvodolorimeter, which uses a cotton swab attached to an air-spring device designed to apply controlled pressure at ever increasing levels, was used to determine the pain threshold at 23 different points on the vulva. In addition, a hydraulic system that applied increasing degrees of pressure, from 0.25 kg/cm2 to 10 kg/cm2, to a 1 cm2 area on the left thumb was used to measure the level of tolerance for pain as well as the pain threshold. Participants (n = 17) were recruited from women 18 to 60 years old who were referred to the authors’ center for vulvar disease for evaluation of vulvodynia. A control group of patients with no vulvar pain (n = 23) was recruited from gynecology clinics and from ads in newspapers. Study participants were more often white with a higher annual income compared with control subjects; otherwise, the 2 groups were similar. The pain threshold of vulvodynia patients was significantly lower at all 23 points on the vulva (range, P = 0.03–<0.001) compared with control subjects. The most sensitive areas were the interlabial sulci, introitus, and midline areas. Right and left locations were equally sensitive. When pain threshold levels from all bilateral points were grouped into 6 regions (thighs, labia majora, interlabial sulci, midline sites, and anterior and posterior introitus), the pain sensitivity threshold was increased for vulvodynia patients in all areas (P ≤0.004). The study subjects had a lower pain threshold at the deltoid, shin, and thumb sites compared with control subjects (P ≤0.05). No differences were seen between pain sensitivity on the right or left sides. Reactions to progressive pressure applied to the thumbnail showed that vulvodynia patients experienced “mild” pain and “slightly intense” pain at significantly lower pressures than control subjects (P = 0.02 and P <0.001, respectively). The pain thresholds in vulvar sites correlated with peripheral sites for both vulvodynia patients and control subjects. There were no differences in perception of pain between white and black patients. The subjective results of a standard cotton-swab test, in which patients rated their pain when various sites on the vulva were touched with a cotton-swab using light pressure, were compared with quantified vulvodolorimeter findings. Strong correlation between the 2 methods was seen at the posterior introitus (6 o’clock) (P <0.001), the introitus (P = 0.001), and the interlabial sulci locations (P = 0.001). No correlation was seen at the labia majora or upper thighs.