Evidence suggests that there is an association between chronic pain and disruption of the body schema. We tested the hypothesis in fibromyalgia syndrome (FMS).
We investigated distinct perceptual aspects of the body schema both in a sample of patients with FMS and in pain-free controls. Performances on the left/right judgment task were measured; tactile acuity was assessed by using the 2-point discrimination test. Furthermore, we evaluated sensations evoked by tactile stimulation with von Frey filaments to body parts that were experiencing pain. Anomalous sensations elicited by sensory-motor conflict (SMC) were also investigated.
Patients with FMS showed inferior performance on the right/left judgment task, both in terms of correct matches (75.38% vs. 89.67%, respectively; P<0.05) and response time (2.58 s vs. 1.89 s, respectively; P<0.05). Effect sizes were large and very large, respectively. Two-point discrimination thresholds were significantly higher (P<0.05) in participants from the FMS sample (mean of 49.71 mm, SD: 12.09 mm) relative to controls (mean of 37.36 mm, SD: 7.81 mm). Nine of 14 participants with FMS, but no control participants, reported referred sensations upon tactile stimulation, including tingling, pins and needles, weight, and cramps. Referral sites included regions both adjacent and remote to stimulated sites. Patients with FMS scored across all items within the administered questionnaire addressing anomalous sensations on the mirror setup (Cohen d=1.04 to 2.42 across all items), and FMS patients perceived pain during the SMC (the required statistical power for it to be statistically significant was 96% and for it to be recognized as a difference of means in pain item).
Our present findings suggest a disrupted body schema and propensity to experiencing anomalous somatosensory sensations during SMC in people with FMS.