To examine the distribution of stress-induced upper-body pain in fibromyalgia patients, and the possible association of pain with electromyographic activity in muscles near the sites of pain development.
Fifteen fibromyalgia patients and 15 pain-free subjects were exposed to low-level mental strain over a one-hour period. EMG was recorded from frontalis, temporalis, trapezius, and splenius capitis. Pain in the corresponding locations was recorded before the test, every 10 minutes during the test, and the 30-minute posttest period.
The fibromyalgia patients developed pain during the test in all the above body locations. Pain development in all locations associated with trapezius EMG activity, but not with EMG activity in underlying muscles for forehead, temples, and neck.
Stress-induced pain in fibromyalgia patients is not generally caused by muscle activity. The trapezius EMG response may be part of a general stress response that cause pain independently of motor activity in muscles.