The size of pain referral patterns from a tonic painful mechanical stimulus is increased in women

Abstract

Abstract Aims The purpose of this study was to investigate potential gender differences in pain referral patterns induced by a tonic painful mechanical stimulus. Methods Forty-five healthy adults (22 women) participated in this study. Pressure pain thresholds (PPTs) were assessed at the infraspinatus, the brachioradialis and the gastrocnemius muscles on the dominant side, using handheld algometry. Following this, painful pressure at the infraspinatus muscle was induced using the algometer by rapidly increasing the pressure until it reached the level of 7 cm on VAS (PVAS7). This pressure was kept constant for 60s. Upon release, the subject was asked to indicate the area of the pressure-induced pain on a digital body chart. PPT values, PVAS7 and the pain area (number of pixels) were extracted for data analysis. Results No gender differences were found in PPT values (P >0.05). The pressure needed to reach 7 cm on the VAS was significantly lower in the female group (687.4±50.5 kPa) compared with males (971.0 ± 49.6 kPa; unpaired t-test: P < 0.05). The size of the pain area following PVAS7 stimulation for 60 s was significantly larger in the female group (12,578.5 ± 17,280.3 pixels) compared with the male group (6175.0 ± 9518.5 pixels; Mann–Whitney-U; P < 0.05). Conclusions Despite comparable PPT values, women demonstrated larger pain areas compared with men although the standardized painful stimulus which intensity was perceived similarly as 7 cm on the VAS scale in both groups. These findings suggest that there are gender-specific differences in pain distribution and referred pain but it is unclear through which mechanism they are mediated.