Ever get the impression that using your brain to think causes your fibromyalgia (FM) pain to get worse? Perhaps you might also find that even mild mental challenges leave you feeling tense and fatigued. Rest assured, this is no fluke. Research shows that using your brain does make your FM symptoms worse, and studies to pinpoint the reason for this phenomenon are ongoing.

Two years ago, Kristian B. Nilsen, M.D., Ph.D., of Norway, reported that FM patients do experience increased pain, fatigue, and tension levels after performing a one-hour computer-based test (see April 2006 Journal).¹ With the aid of surface-electromyographic (S-EMG) probes placed on several muscles, Nilsen showed that the aggravation of FM symptoms were not caused by increasing muscle activity or tensing up one’s muscles during a mental stress test. He has since conducted two more studies to better understand why FM symptoms worsen during an easy mental challenge a 10-year old could breeze through.

Cardiovascular ResponseIn addition to using S-EMG to measure muscle tension, Nilsen also collected blood samples and measured cardiovascular parameters during the one-hour test and for a 30-minute rest period that followed. The goal of this part of the study was to determine if mental stress activated the autonomic nervous system, leading to a worsening of FM symptoms.² More specifically, Nilsen assessed whether the sympathetic branch of the autonomic nervous system (which controls cardiovascular function) responded differently in FM patients versus healthy controls. And, if so, did any altered responses relate to the pain produced by the mental challenge?

Stress, even if it is a mild mental challenge, should increase heart rate, and this is what happened in the healthy control group. The average increase in heart rate was five beats per minute, but regardless of the heart rate change for each control subject, their pain scores did not increase with the change in heart rate. The findings were very different for the FM group in which the cardiovascular response to the stress appeared to be blunted. In general, FM patients responded to the mental stress with a smaller heart rate response (a few actually experienced a drop in heart rate), and lower heart rates corresponded to greater pain levels.

What about changes in blood pressure? One would expect stress to trigger an elevation in blood pressure, at least initially until the body acclimates to the situation. Nilsen found that the blood pressure spiked during the beginning of the stressful task for the healthy controls but hardly changed for the FM patients.

Nilsen also found elevated norepinephrine levels in the blood of FM patients compared to the healthy control group. Norepinephrine is the neurotransmitter released by the sympathetic nervous system. Nilsen wondered if the enhanced pain response to the computer test could involve sympathetic activation of the muscles. However, another study was needed to determine the role of the sympathetic system in aggravating FM pain during a mental challenge.

Sympathetic BlockadeNilsen tested this theory by injecting an anesthetic to block the sympathetic nerves supplying the neck/shoulder muscles on one side of the body in 10 FM patients just before putting them through the mental tasks.³ S-EMG probes were placed on the subjects to evaluate muscle activity during the one-hour computer-based test followed by a 30-minute rest period.

If the sympathetic system was responsible for the worsening of FM symptoms during the test, then the side with the blockade should not change. As it turned out, the FM patients experienced a worsening of FM symptoms on both sides of their body, so the sympathetic system is probably not causing the increased pain that occurs during a mental task.

Where is this Leading?Most people (including one’s physician) often view muscular pain as being caused by overly tensed muscles. In turn, the pain is assumed to be the result of the body’s stress response mechanisms, particularly the sympathetic nervous system. If this were the case, one would just have to relax to ease pain. However, this series of studies by Nilsen show that these simplistic and commonly made assumptions are not true for people with FM.

When FM patients challenged their brains, their cardiovascular response was the opposite of what one would expect. But what exactly could be responsible for the reduced heart rate? Nilsen says, “It is most likely to have a central nervous system cause.” Further studies should look for abnormalities between the way the central and sympathetic nervous systems communicate with one another.

1. Nilsen KB, et al. Eur J Pain 10:615-27, 2006.
2. Nilsen KB, et al. Eur J Pain 11:743-55, 2007.
3. Nilsen KB, et al. Scand J Rheumatol 37:53-61, 2007.

• Leave a comment...