Fibromyalgia has been researched extensively over the past 5 – 10 years. I remember when it was a diagnosis of ‘last resort’ and almost became a condition to ‘dump’ patients who had widespread pain but few signs. It didn’t seem to make much difference to treatment either!
Now it looks like there is an ever-increasing range of studies showing the role of central sensitisation in the disorder. And as someone who meets criteria for fibromyalgia, I was interested to read this post by ‘ByTheBay’ where the results from a study by Geisser, Glass, Rajcevska, Clauw, Williams, Kileny & Gracely are discussed.
The hypothesis being tested was that “subjects with FM would display greater sensitivity to both pressure and auditory tones and report greater sensitivity to sounds encountered in daily activities.”
A group of 30 participants diagnosed with fibromyalgia and a group of 28 controls were identified, and were administered auditory tones and pressure using the same psychophysical methods to deliver the stimuli and a common way of scaling responses. Subjects were also administered a self-report questionnaire regarding sensitivity to everyday sounds. The findings?
Subjects with FM displayed greater sensitivity to pressure stimulation to the thumb compared with healthy control subjects for low-, medium-, and high-pressure intensities. The mean pressure needed to evoke these sensations for FM subjects were significantly lower than for healthy control subjects. As with pressure stimulation, significantly lower auditory stimulation was needed to evoke ratings of low, medium, and high pain intensity in FM subjects compared with healthy control subjects. In addition, subjects with FM reported having significantly greater hearing sensitivity on the hyperacusis questionnaire compared with healthy control subjects.
Consistent with prior research, subjects with FM demonstrated greater sensitivity to auditory tones compared with healthy control subjects. They also reported significantly greater sensitivity to daily sounds. Within both the patient and control groups, sound and pressure sensitivity measures were related to each other, suggesting a common underlying mechanism associated with these phenomena. Thus, these data lend further credence to the notion that FM is in part due to a global disturbance in sensory processing rather than an isolated abnormality in pain processing.
There are some limitations to this study: one is the cross-sectional design – it’s not apparent whether increased sensitivity occurs as a result of fibromyalgia, or predisposes to fibromyalgia. Sample sizes for both groups are small – and the steps for selecting ‘normal’ controls isn’t well-described. The statistical tests lacked power, so that even moderate effect sizes didn’t reach significance. It’s also not clear whether any other groups of people with chronic pain have similar increased sensitivity.
What does it mean?
Well, apart from recognising that people with fibromyalgia are sensitive souls, it may point to a central neurobiological deficit in sensory processing. This may lead to future studies using fMRI, PECT and other imaging modalities to identify the specific areas of the brain that may be responsible for this sensitivity. It may lead to development of therapies similar to those used for developmental delay disorders such as sensory integration, or even a process of a graded desensitisation.
In the meantime, it might be helpful for people who have fibromyalgia to be aware of their tendency to become aware of and respond to sensory stimuli, and take steps to avoid ‘over-stimulation’. For example, it might be useful to wear sunglasses in glarey or bright light, to use earplugs when it is noisy (especially when trying to sleep), and to introduce new sensations such as fabric textures, tastes etc slowly.
Geisser, Glass, Rajcevska, Clauw, Williams, Kileny & Gracely (2008). A Psychophysical Study of Auditory and Pressure Sensitivity in Patients With Fibromyalgia and Healthy Controls, Journal of Pain, in press