The diagnosis of fibromyalgia in women may be influenced by menstrual cycle phase

SummaryThis investigation evaluated changes in pressure pain threshold (PPT) in 11 healthy females during three phases of the menstrual cycle: menstrual (day 3 following onset of menses), follicular (days 12–13), and luteal (day 21). PPTs were measured with an algometer at nine anatomical locations, bilaterally, for a total of 18 sites. The sites chosen serve as one criterion for the diagnosis of fibromyalgia, which requires the presence of tenderness at ⩾11 of these sites, with a PPT of ⩽4 kg. When measured as a continuous variable over the course of two sequential menstrual cycles, mean PPT measurements during the menstrual phase (3.40±1.12 kg), follicular phase (3.44±1.17 kg), and the luteal phase (3.56±1.14 kg) were not statistically significant. However, when PPT data were converted to dichotomous, discrete variables (either ⩽4 or >4 kg), five participants “changed” fibromyalgia diagnosis during the course of a menstrual cycle, fulfilling the PPT criterion (⩽4 kg at ⩾11 points) during the luteal phase (n=3) or menstrual phase (n=2), but never during the follicular phase. We compare these results with previous studies, and discuss influences upon PPT by hormonal fluctuations, the endorphin system, and the endocannabinoid system. In summary, clinicians should appreciate that sensitivity to pressure and pain varies over the course of the menstrual cycle, requiring clinical adjustments in palpation-based diagnostic models and treatment modalities.