Abstract: FMRI Evaluation of Pain Intensity Coding in Fibromyalgia Patients and Controls

Aim: Tenderness is a defining attribute of fibromyalgia (FM). Using functional MRI (fMRI) imaging in previous studies, we found evidence that tenderness in FM results from a central augmentation of pain perception. This study used fMRI to evaluate a new cohort of FM patients and healthy controls in order to identify supraspinal structures that show graduated responses to increasing levels of painful pressure.

Methods: Pressure stimuli producing subjective levels of low, moderate and high pain were determined for 18 FM patients and 9 healthy controls. In subsequent 10min fMRI sessions, these pressures were applied in random order (25s stimulus duration, 50s interstimulus interval) to the left thumb nail bed. FMRI scans of the entire brain were obtained at 5s intervals. The data were intensity normalized, spatially smoothed and transformed into standard space.

Results: A comparison of the high pain stimulus and rest showed similar activations in both groups in contralateral primary and secondary somatosensory cortex, inferior parietal lobule, anterior insula, putamen and ipsilateral cerebellum. Correlating the three levels of painful stimuli with the fMRI signal showed similar associations in both groups in contralateral primary and secondary somatosensory cortex.

Conclusion: The results support our previous findings that similarly subjectively intense stimuli, produced by lower levels of stimulation in FM, result in comparable increases in the fMRI signal in clinical and control subjects. The correlation between stimulus intensity and cerebral response in the contralateral somatosensory regions indicates that the mechanisms responsible for pain amplification in FM preserve the pattern of stimulus intensity coding in the CNS observed in healthy controls.

Disclosure: This study was supported by Army grant 17-00-6042.

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