Do Fibromyalgia patients have any abnormalities on brain imaging to support a central mechanism for their amplified pain perception?
Brain MRIs are normal in FM patients. However, functional imaging studies using single-photon emission computed tomography (SPECT) scans and fMRI have shown decreased regional cerebral blood flow to the thalamus and caudate nucleus in FM patients compared with healthy individuals. The caudate nucleus and thalamus signal noxious stimuli, and decreased blood flow to these areas has been demonstrated in other chronic pain disorders. One explanation for these findings is that the widespread pain in FM activates inhibitory mechanisms in an attempt to reduce the evoked activity in the thalamus and decrease pain processing. With reduced activity, the thalamus needs less blood flow. An alternative explanation is that it takes less stimulation of the thalamus to induce pain in patients with FM, or that patients with FM have decreased gray matter density in the thalamus. The reduced blood flow to the caudate may indicate an abnormal dopaminergic system, which is important in pain modulation, pleasure perception, and motivational responses.
fMRI has also shown increased blood flow, connectivity and activity in the insula, anterior cingulate cortex, and primary and secondary somatosensory cortices in response to painful stimuli. These are all areas that are involved with pain perception and emotional modulation from any cause of chronic pain. These findings on fMRI support a physiologic basis causing a FM patient’s increased perception of pain.