Preliminary investigation of absent nociceptive flexion reflex responses among more symptomatic women with fibromyalgia syndrome

Abstract

Fibromyalgia syndrome (FMS) is a widespread musculoskeletal pain condition with unclear physiologic mechanisms. The purpose of this investigation was to compare the responsiveness of nociceptive flexion reflex (NFR) pathways between women with and without FMS. A secondary purpose was to examine the influence of depression, fibromyalgia symptom severity, and cardiovascular health on NFR responses among women with FMS. Fifteen women with FMS and 14 healthy controls participated in an experimental session to assess NFR responses to sural nerve stimulation, resting mean arterial pressure (MAP) and heart rate (HR), and scores on the Beck Depression Inventory (BDI) and Fibromyalgia Impact Questionnaire (FIQ). NFR responses were successfully elicited from all healthy individuals, but only eight (53 %) of the women with FMS. These women did not differ in the minimum stimulus intensity required to elicit an NFR response compared to healthy controls (p ≥ 0.35). Further, these women had lower BDI (p = 0.04) and FIQ (p = 0.02) scores compared to women with FMS from whom NFR responses could not be elicited. Resting HR was higher in both groups of women with FMS compared to healthy individuals (p < 0.05), and MAP was strongly associated with NFR thresholds only among women with FMS (r = 0.88, p < 0.01). Findings from this preliminary investigation suggest that NFR pathways are impaired in women who are more severely impacted by symptoms of depression and fibromyalgia, potentially due to desensitization of NFR pathways with chronic autonomic arousal.

Conflict of interest statement

Conflict of interest Authors declare no conflicts of interest.

Figures

Fig. 1

a Beck Depression Inventory (BDI) scores were significantly lower for healthy women (n = 14) compared to women with fibromyalgia syndrome (FMS; n = 15). b BDI scores were significantly lower for women with fibromyalgia in the nociceptive flexion reflex responder (NFR-R) group compared to the NFR nonresponder (NFR-NR) group. c Fibromyalgia Impact Questionnaire (FIQ) scores were also significantly lower for the NFR-R group compared to the NFR-NR group. Bars indicate group mean (SEM)

Fig. 2

Nociceptive flexion reflexes (NFR) in the biceps femoris muscle are shown for representative women from the healthy control group (a), the NFR responder group (b), and the NFR nonresponder group (c). A positive NFR response was defined as an increase in the rectified electromyographic (EMG) signal within a time window corresponding to the NFR latency (90–150 ms after delivery of a train of electrical stimuli to the sural nerve) that exceeded the mean pre-stimulus EMG by ≥1 SD. Note that no NFR response was detected for the individual shown in (c) at the maximum stimulus intensity of 40 mA (relative stimulus intensity = 19 × perceptual threshold)

Fig. 3

The nociceptive flexion reflex threshold (NFRT) was positively correlated with resting mean arterial pressure (MAP) in women with FMS (a), but not in healthy women (b)