Pain chronobiology in clinical trial participants with fibromyalgia: a comparison with neuropathic pain.

INTRODUCTION

Diurnal pain rhythmicity is well recognized for neuropathic pain (NP) and osteoarthritis, however, less is known for fibromyalgia.

OBJECTIVE

We conducted secondary analyses of clinical trial data to describe pain rhythmicity in fibromyalgia compared to NP.

METHODS

We have compared morning-evening pain differences in fibromyalgia with that of NP by conducting exploratory analyses of data from 2 fibromyalgia trials (68 pooled participants) and 1 NP trial (55 participants). In these trials, pain intensity (0-10 scale) was rated at 8:00 am and 8:00 pm during a 7-day pretrial baseline period and throughout each trial. Analyses evaluated morning vs evening pain intensity differences for each condition as well as possible patient-specific predictors of diurnal variability.

RESULTS

Data demonstrated statistically significant morning-evening differences in both conditions such that evening pain was higher than morning pain by approximately 20% in NP (0.97 NRS, CI: 0.77-1.16) and approximately 7% in fibromyalgia (0.38 numerical rating scale (NRS), CI:0.22-0.53). The morning-evening pain intensity difference was significantly greater for NP vs fibromyalgia. In exploratory analyses of participants with fibromyalgia, older age, shorter pain duration, and more severe "hot-burning" pain rating were significantly correlated with greater morning-evening differences. In NP participants, higher body weight and higher pain interference were significantly correlated with lower morning-evening differences.

CONCLUSIONS

These analyses suggest that fibromyalgia pain is slightly more intense in the evening vs morning. Although it seems less pronounced than with NP, patient subgroups with this pattern should be studied further when investigating and implementing fibromyalgia treatment interventions.