Background: Recent findings highlighted the clinical relevance of within subjects’ variability of pain scores in response to both experimental and clinical pain. Fibromyalgia (FM), a chronic pain condition which is characterized with impaired pain descending modulatory system and larger within-subject pain variability, offers an opportunity to further investigate this topic. The aim of this study was to investigate relationships between experimental pain variability and pain sensitivity and pain modulation in FM. 
Methods: FM patients underwent a battery of experimental pain tests, comprised of various noxious modalities (electrical, thermal, pressure) and assessing pain sensitivity (threshold, tolerance), modulation (Temporal Summation and Conditioned Pain Modulation) and experimental pain variability (FAST). Information related to symptoms and psychological characteristics was also collected.
Results: Twenty-nine FM patients completed the study. There were no consistent relations between FAST and sensitivity, nor relations between experimental pain variability and pain modulation measures.
Conclusion: In summary, as seen in a recent healthy subjects’ study, in FM population there are no relations between the within-subjects variability in response to experimental stimuli and the sensitivity to pain or pain modulation.

WITHIN-SUBJECTS VARIABILITY OF EXPERIMENTAL PAIN AND ITS RELATIONS WITH PAIN SENSITIVITY AND PAIN MODULATION IN FIBROMYALGIA