Altered Spinal Excitability in Patients with Primary Fibromyalgia: A Case-Control Study

Reevaluating fibromyalgia diagnosis: a proposal to integrate deep tendon reflex responses into current criteria

Fibromyalgia is a complex condition characterized by widespread pain, fatigue, and various other symptoms. The symptoms of fibromyalgia overlap with numerous other disorders (e.g., infections, chronic fatigue syndrome), which makes diagnosis challenging. Existing diagnostic criteria for fibromyalgia rely particularly on subjective patient reports. Such a limitation may lead to both missed diagnoses and potential overdiagnoses. Recent research has identified significantly increased deep tendon reflex (DTR) responses in patients with fibromyalgia. The results also demonstrated the potential for DTR examination to help with the diagnostic process, particularly with ruling out fibromyalgia. The potential underlying mechanisms behind the increased DTR responses in fibromyalgia are central nervous system dysregulation, altered muscular properties, autonomic nervous system dysfunction, and accompanying conditions such as hypomagnesemia and anxiety. By integrating DTR responses into current diagnostic criteria sets, physicians may more effectively differentiate fibromyalgia from other conditions and avoid the pitfalls of misdiagnosis, as well as overdiagnosis. The use of DTR testing in the diagnostic evaluation of fibromyalgia shows promise. Yet, it has both advantages and limitations. The potential benefits of this approach include improved diagnostic accuracy, but challenges remain in its low specificity. This means that hyperreflexia testing alone is not definitive in diagnosing fibromyalgia. Nonetheless, given the high sensitivity, a decreased DTR response could still contribute to ruling out fibromyalgia.

Diagnostic utility of deep tendon reflex responses in rectus femoris and triceps brachii in fibromyalgia: a clinical and electrophysiological study

The aim of this study was to evaluate deep tendon reflex responses and associated electrophysiological parameters of the muscles in patients with fibromyalgia. This cross-sectional study included 38 patients with fibromyalgia and 32 age- and sex-matched controls. Deep tendon reflexes of the rectus femoris and triceps brachii were tested using a reflex hammer. Electromyographic (amplitude and duration of activation), inertial measurement unit (angular velocity, acceleration), and electromechanical (delay) analyses were performed using a surface electromyography (sEMG) device. Comparative analyses were carried out between patients and controls. Additionally, Receiver Operating Characteristic (ROC) analysis was performed to evaluate the ability of hyperreflexia in distinguishing fibromyalgia patients from controls. Hyperactive deep tendon reflexes in the right/left rectus femoris and/or triceps brachii were observed in more than 85% (ranging from 86.8 to 94.7%) of the fibromyalgia group. Patients with fibromyalgia exhibited significantly increased deep tendon reflex responses compared to controls (p < 0.001). Patients revealed significantly higher amplitude, longer duration of muscle activation, greater sagittal acceleration and angular velocity, and shorter electromechanical delay. Normalized muscle activation (right and left rectus femoris and right triceps brachii) in response to deep tendon reflex test showed acceptable ability in differentiating fibromyalgia patients from controls (Area under curve (AUC) = 0.890, 0.784 and 0.782, respectively). For the right rectus femoris, values ≤ 28.3 (clinically corresponding to normoactive/hypoactive deep tendon reflexes) appeared to rule-out fibromyalgia with 94.1% sensitivity and 61.3% specificity. Patients with fibromyalgia exhibit increased deep tendon reflex responses. Normal or decreased deep tendon reflex responses may probably be used as a rule-out criterion for fibromyalgia.

Evidence for spinal disinhibition as a pain-generating mechanism in fibromyalgia syndrome

Introduction

Pain phenomenology in patients with fibromyalgia syndrome (FMS) shows considerable overlap with neuropathic pain. Altered neural processing leading to symptoms of neuropathic pain can occur at the level of the spinal cord, and 1 potential mechanism is spinal disinhibition. A biomarker of spinal disinhibition is impaired H-reflex rate-dependent depression (HRDD).

Objectives

This study investigated whether patients with FMS exhibit evidence of spinal disinhibition.

Methods

Thirty-one individuals with FMS and 20 healthy volunteers underwent testing of Hoffman reflex including HRDD, along with assessment of clinical signs and symptoms, pressure pain thresholds, temporal summation of pain (wind-up), and conditioned pain modulation (CPM). Small nerve fibre structure was quantified using intraepidermal nerve fibre density and corneal confocal microscopy.

Results

Patients with FMS had significantly impaired HRDD at 1 Hz (P = 0.026) and 3 Hz (P = 0.011) and greater wind-up ratio (P = 0.008) compared with healthy controls. Patients with the most impaired HRDD also had the most inefficient CPM but HRDD was not associated with wind-up. Both HRDD and CPM were most impaired in patients with a shorter duration of disease.

Conclusion

We demonstrate for the first time that people with FMS show evidence of spinal disinhibition, which is most dominant in shorter duration of disease and may represent a putative mechanism of pain generation in FMS. Identifying people with impairment of central pain processing at an early stage may provide opportunities for targeted mechanistically directed interventions. Longitudinal studies are warranted to tease out the precise contribution of these mechanisms.

Mechanisms of transcranial direct current stimulation (tDCS) for pain in patients with fibromyalgia syndrome

Fibromyalgia syndrome (FMS) is a recurrent pain condition that can be challenging to treat. Transcranial direct current stimulation (tDCS) has become a promising non-invasive therapeutic option in alleviating FMS pain, but the mechanisms underlying its effectiveness are not yet fully understood. In this article, we discuss the most current research investigating the analgesic effects of tDCS on FMS and discuss the potential mechanisms. TDCS may exert its analgesic effects by influencing neuronal activity in the brain, altering cortical excitability, changing regional cerebral blood flow, modulating neurotransmission and neuroinflammation, and inducing neuroplasticity. Overall, evidence points to tDCS as a potentially safe and efficient pain relief choice for FMS by multiple underlying mechanisms. This article provides a thorough overview of our ongoing knowledge regarding the mechanisms underlying tDCS and emphasizes the possibility of further studies to improve the clinical utility of tDCS as a pain management tool.

Temporal Investigations of the Changes in Presynaptic Inhibition Associated With Subthalamic Nucleus-Deep-Brain Stimulation

BACKGROUND AND PURPOSE

There are controversies regarding the role of presynaptic inhibition (PSI) in the mechanisms underlying the efficacy of deep-brain stimulation (DBS) in Parkinson's disease (PD). We sought to determine the involvement of PSI in DBS-related mechanisms and clinical correlates.

METHODS

We enrolled PD subjects who had received subthalamic nucleus DBS (STN-DBS) therapy and had been admitted to our clinic between January 2022 and March 2022. The tibial H-reflex was studied bilaterally during the medication-off state, and all tests were repeated 10 and 20 minutes after the simulation was turned off. Simultaneous evaluations based on the Movement-Disorder-Society-sponsored revision of the Unified Parkinson's Disease Rating Scale part III (MDS-UPDRS-III) were performed in all of the patients.

RESULTS

Ultimately we enrolled 18 patients aged 58.7±9.3 years (mean±standard deviation, 10 females). Fifty percent of the patients showed a decrease in the MDS-UPDRS-III score of more than 60% during the stimulation-on period. Comparative analyses of the repeated measurements made according to the stimulation status revealed significant differences only in the left H-reflex/M-response amplitude ratio (H/M ratio). However, no difference in the left H/M ratio was found in the subgroup of patients with a prominent clinical response to stimulation (n=9). Analyses of the less-affected side revealed differences in the H-reflex amplitude and H/M ratio.

CONCLUSIONS

We found evidence of PSI recovery on the less-affected side of our PD subjects associated with STN-DBS. We hypothesize that the involvement of this spinal pathway and its contribution to the mechanisms of DBS differ between individuals based on the severity of the disease and which brainstem regions and descending tracts are involved.

Investigation of the changes in the presynaptic inhibition in association with the subthalamic nucleus stimulation in Parkinson's disease

BACKGROUND AND PURPOSE

Presynaptic inhibition (PSI) is a critical spinal inhibitory mechanism for modulating muscle coordination by adjusting both supraspinal motor commands and sensory feedback at the spinal level. The literature data regarding the role of PSI in the efficiency of STN-DBS therapy in Parkinson's disease (PD) are limited. We aimed to investigate the possible alteration in this pathway in association with the STN stimulation (STIM) within the very early period after the STIM is off.

METHODS

We performed the H-reflex investigation on 8 PD subjects with STN-DBS who applied to our polyclinic for routine clinical evaluations. The investigations were initially performed at the STIM-on period and repeated after the STIM set is off for 5 min. A within-subjects ANOVA was used to test for a significant difference between the STIM-on and -off states for the variables of (repeated measures) H-latency, H amplitude, M amplitude, H/M amplitude, H threshold, and M threshold.

RESULTS

The results of the analyses did not reveal marked changes in the variables of the H-reflex between the STIM-on and -off states.

CONCLUSION

PSI do not alter in the very early period after the STIM is off. Taken together with the related literature data and our study results, it can be hypothesized that the PSI might involve in the DBS efficiency in the later phase of the STIM as a compensatory mechanism. Further prospective studies including a larger number of patients with serial electrophysiological recordings to investigate the temporal course of the underlying dynamics are required to clarify these discussions.