Results
A total of 313 individuals with diagnosed ME/CFS underwent HUT during the study period. PPT testing was not performed due to increased severity of hand pain (often in those with hypermobile joints) (n=50); 15 patients refused PT testing. None of the patients used HR or BP altering drugs before the measurements. This left 248 females to be analyzed. One-hundred-sixty-four patients (66%) fulfilled the criteria for FM, eighty-four (34%) did not. As part of the ME/CFS criteria, patients were asked for the presence of muscle complaints. In the group of ME/CFS patients without FM 59/84 (70%) reported muscle pains. In ME/CFS patients with FM, all patients 164/164 (100%) reported muscle pains.
Table 1 shows the demographic characteristics of the study population. The NRS pain score was significantly different between the three groups (p all <0.0001). ME/CFS patients with and without FM showed higher supine heart rates compared to HC (p<0.0005 and p<0.002, respectively) and higher EOS heart rates compared to HC (both p<0.0001). No other variables were significantly different.
Table 2 shows PPT pre- and post-HUT for the finger and the shoulder. PPT of HC were all significantly higher than of ME/CFS patients (p ranging between <0.005 and <0.0001), except for PPT of the finger in ME/CFS patients without FM (p=0.41). Ninety-six ME/CFS patients (38%) used neuropathic pain medication, 14/84 (17%) in patients without FM and 82/164 (50%) in patients with FM. A subgroup analysis showed no differences in PPT between ME/CFS patients with FM using neuropathic pain medication compared to those without. Similarly, no differences in PPT were found between ME/CFS patients without FM using neuropathic pain medication or not (data not shown). Figure 1 shows PPT pre- and post-HUT for the finger and the shoulder in HC (panel A), in ME/CFS patients without FM (panel B), and in ME/CFS patients with FM (panel C). PPT of the finger were significantly higher than PPT of the shoulder in all 3 groups (all p<0.0001). PPT of HC did not differ pre- and post-HUT for both the finger and the shoulder (p=0.14 and p=0.54, respectively). In both ME/CFS patient groups there was a significant difference pre- and post-HUT for both the finger and the shoulder (p ranging between 0.0001 and <0.0001). PPT of ME/CFS patients with FM were significantly lower than PPT of ME/CFS patients without FM (all p<0.0001).
Figure 2 shows the graphical representation of the regression line in the 3 groups for the finger (panel A) and the shoulder (panel B). For all time points and groups, the linear regression of windup from stimulus one to ten on both finger and shoulder were highly significant (p ranging from 0.0003 to <0.0001). The slopes of the regression lines pre- and post-HUT for both ME/CFS patient groups were significantly higher than the slopes of the pre- and post-HUT regressions lines of HC (all p<0.0001). There was no difference in the regression line slopes between pre- and post-HUT within the 3 groups for both the finger and the shoulder. For comparison with the published literature, stimulus 1 pain values were subtracted from stimulus 10 pain values to create a delta windup value. As shown in Figure 3, for both the finger and the shoulder, delta windup values did not differ between pre- and post-HUT in HC and the 2 ME/CFS patient groups. For both locations a statistically significant difference was found between HC and the 2 ME/CFS patient groups (both p<0.0001).