Beth Skwarecki
September 17, 2014
Brain scans of patients with fibromyalgia showed that they processed nonpainful stimuli, such as sound and touch, differently than the brains of people without the disorder. This may explain why patients often complain of hypersensitivity to sensations in everyday life, author Marina López-Solà, PhD, from the Department of Psychology and Neuroscience at the University of Colorado, Boulder, told Medscape Medical News.
“What we wanted to know is whether in fact there was something in the brain that would account for these feelings in response to stimulation that is not painful in nature,” Dr. López-Solà said. The study, published online September 15 in Arthritis & Rheumatism, used functional magnetic resonance imaging to show that patients with fibromyalgia processed visual, auditory, and tactile sensations with reduced brain activity in primary sensory processing areas, combined it with higher activity in sensory integration areas such as the insula, compared with individuals without fibromyalgia.
The study involved 35 patients with fibromyalgia and 25 control participants recruited in Barcelona, Spain. All participants were women and were right handed, and a neurological exam showed they had normal vision and hearing. Patients met the 1990 American College of Rheumatology criteria for fibromyalgia and had a mean illness duration of 7 years. Patients were asked to continue any regular medical treatment but to avoid rescue analgesics for 72 hours before imaging. The researchers excluded control participants if they had chronic or acute pain, substance abuse, or a history of psychiatric illness or other relevant disorders.
Patients rated their spontaneous pain higher (mean, 71.29 ± 15.87) compared with control participants (all rated their pain as 0) and also showed higher subjective sensitivity to visual (21.51 vs 11.56; P < .0001), auditory (16.89 vs 5.16; P < .0001), and tactile (18.80 vs 11.81; P < .0001) stimuli. These hypersensitivity measures correlated strongly with clinical symptoms.
During the imaging, participants experienced 4 cycles of 30-second periods of rest alternated with sensory activation. The sensory activation included 3 things simultaneously: a flashing checkerboard pattern, an auditory stimulus with beeps in an unpredictable pattern, and for a tactile stimulus, the patients were asked to touch their thumb to each finger. Dr. López-Solà describes all 3 things as sensations most people would consider slightly unpleasant.
“The alteration we were most surprised about was a hyporesponse in primary auditory and visual processing,” Dr. López-Solà said. Patients showed reduced activation in primary and secondary auditory cortices, middle temporal gyri, hippocampi, ventral basal ganglia, and BA17 and parts of BA18 in the inferior occipital gyri.
Patients also showed increased processing in right insula extending to the opercula and the anterior part of the lingual gyrus contiguous with the parahippocampal gyrus. “The brain seems to be hypoprocessing at a basic first level of cortical processing, then amplifying the signal at a later level,” Dr. López-Solà said.
Dr. López-Solà believes these processing abnormalities may explain why patients sometimes avoid certain sensations; for example, wearing sunglasses indoors or withdrawing from social activities as simple as loud conversations.
Recognizing the connection between pain and hypersensitivity may help clinicians who might otherwise dismiss symptoms of pain in a patient who, Dr. López-Solà said, seems to “complain basically about everything.” She speculates that sensory treatments such as whole-body vibration or even Tai Chi, which has shown some effectiveness in patients with fibromyalgia, may help patients adjust the way they process sensations and perhaps alleviate pain.
The study “adds more weight to the fact that there is some kind of very real disorder in people with fibromyalgia that is more of a central nervous system problem rather than something out in the periphery causing pain,” Jennifer Glass, PhD, from the Research Center for Group Dynamics at the University of Michigan, Ann Arbor, told Medscape Medical News.
However, Dr. Glass, who was not involved in the study, points out that the number of participants — although large for a neuroimaging study — is small enough to merit caution in generalizing to all people with fibromyalgia.
The authors have disclosed no relevant financial relationships.
Arthritis Rheum. Published online September 15, 2014. Abstract