ANN ARBOR, Michigan—Fibromyalgia (FM) has been suspected of involving a disturbance in pain processing in the central nervous system (CNS), but the problem may be broader. Michael E. Geisser, PhD, reports in The Journal of Pain that FM is associated with a global augmentation of sensory processing in the CNS.¹

“Muscle tenderness is the hallmark of FM, but the findings of this study and others suggest that persons with FM display sensitivity to a number of sensory stimuli. These findings suggest that FM is associated with a global CNS augmentation of sensory information. These findings may also help to explain why persons with FM display a number of comorbid physical symptoms other than pain,” said Dr. Geisser, of the chronic pain and fatigue research center at the University of Michigan in Ann Arbor.

Randomly presented auditory, pressure stimuli

The study included 30 FM subjects and 28 healthy controls, all of whom were tested using auditory tones, pressures, and a self-report questionnaire regarding sensitivity to everyday sounds.

Dr. Geisser emphasized that subjects were tested using auditory loudness stimuli and pressure sensitivity stimuli presented in precisely the same testing paradigms in random sequences. Most previous studies used “ascending” methods by gradually increasing the intensity of the stimulus. “These methods led to reporting biases by subjects, and individuals who are more ‘expectant’ or who have higher levels of distress will rate a sensory experience as being more aversive or unpleasant than individuals who do not have these features. Thus, it is possible that previous findings of a decreased threshold to sensory stimuli could primarily be due to comorbid distress or to expectancy among the FM participants (relative to the control subjects) rather than due to a fundamental defect in sensory processing,” he said.

The researchers expected that, compared with controls, FM subjects would be more sensitive to and that they would more closely rate both sound and pressure. As expected, the investigators found that FM subjects had greater sensitivity to pressure stimulation applied to the thumb and greater sensitivity to auditory stimulation than controls. The subjects also had significantly greater auditory sensitivity.

“Participants with FM displayed significantly greater sensitivity to all levels of auditory stimulation (P <.05). The magnitude of difference between FM patients' lowered auditory sensitivity (relative to control subjects) was similar to that seen with pressure, and pressure and auditory ratings were significantly correlated in both control subjects and subjects with FM. FM patients also were more sensitive to everyday sounds (t = 8.5, P <.001),” Dr. Geisser reported.

Fibromyalgia not due just to abnormal pain processing

The investigators conclude that the findings support an association of FM with a global CNS augmentation in sensory processing. The next step in exploring this association is expected to be neuroimaging studies. Dr. Geisser would like to see studies exploring whether FM patients have heightened responses in the insula compared with healthy controls in response to nonpainful stimuli (sounds), because this area of the brain is suspected of being part of an interoceptive system activated in response to sensations from within the body such as pain, hunger, or thirst.

Dr. Geisser added, “It would be beneficial to examine whether interventions for FM that alter treatment tenderness also affect the processing of other stimuli, such as auditory tones.”

Reference
1. Geisser ME, Glass JM, Rajcevska LD, et al. A psychophysical study of auditory and pressure sensitivity in patients with fibromyalgia and healthy controls. J Pain. 2008;9:417-422.