Background/Purpose: Central sensitization has been demonstrated in patients with fibromyalgia (FM) using an objective assessment of spinal nociception called the nociceptive flexion reflex (NFR). This reflex is measured (electromyographically) as the withdrawal of a proximal leg muscle (biceps femoris) in response to an electrical stimulus applied over the sural nerve. The lowest level of electrical stimulation that generates a measurable withdrawal response is called the NFR threshold. A low NFR threshold (i.e., augmented nociceptive responsivity) has been demonstrated in FM when compared to healthy controls. In this report we sought to determine the prospective association of the change in the NFR threshold with global FM severity (as measured by the Fibromyalgia Impact Questionnaire/FIQ-total score).

Methods:

This is a secondary data analysis of a 12-week randomized clinical trial of the effect of cognitive behavioral therapy (CBT) on nociceptive responsivity and global FM severity. Female subjects who met the 1990 Classification Criteria for FM were randomized to 1 of 2 treatment arms: six weekly sessions of CBT or usual care (UC). Subjects were evaluated at 3 time points: baseline, week 6 (post-intervention) and week 12. For these analyses, the predictor was the baseline-to-week 6 change in NFR threshold and the primary outcome was the FIQ-total at week 12. Linear regression analyses were controlled for treatment group assignment, baseline use of opiates, anticonvulsants and serotonin-norepinephrine reuptake inhibitor (SNRI), and other potential confounders. We considered a variable as a potential confounder if the variable was associated with boththe predictor and the primary outcome.

Results:

The 32 female participants had a mean (± standard deviation) age of 47 ± 12 years; 81% were white, 94% had ≥ high school education, and 44% were employed. At baseline, the sample had a mean disease duration of 12 ± 6 years; 16 (50%) were on opiates; 9 (28%) were on anticonvulsant; and 7 (22%) were on SNRI. Based on the Patient Health Questionnaire-8 (score ≥ 10), 16 (50%) of the participants had probable depression. The mean FIQ-pain score was 5.0 ± 2.3, and the mean FIQ total score was 61 ± 16, suggesting a moderate-to-severely ill patient population. The mean change in NFR threshold (week 6 minus baseline) was – 1.76 ± 13.32 mA, suggesting a reduction in nociceptive responsivity for the entire group.

None of the other baseline variables were associated with both the predictor and the primary outcome.

Conclusion:

Our study is the first to demonstrate that a prior change in NFR threshold predicted future global disease severity in FM. Specifically, a reduction in nociceptive responsivity was (marginally) associated with better clinical status in female FM patients. If corroborated in a larger study, the change in NFR threshold may be a surrogate marker of improvement (or worsening) of overall FM symptomatology.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/nociceptive-flexion-reflex-threshold-possible-surrogate-marker-of-symptom-severity-in-fibromyalgia/