Diffuse central sensitization in low back patients: A secondary analysis of cross-sectional data including tender point examination and magnetic resonance imaging of the lumbar spine

Effects of transcutaneous electrical nerve stimulation on pain, function, and descending inhibition in people with non-specific chronic low-back pain: a study protocol for a randomized crossover trial

BACKGROUND

Low back pain (LBP) is a significant public health problem, is very prevalent, and is often characterized by the persistence of symptoms. Transcutaneous electrical nerve stimulation (TENS) may benefit people with chronic LBP because it can activate descending inhibitory pathways and inhibit central excitability. However, previous studies that have investigated the effects of TENS on pain in people with LBP have failed to use proper intensities of current, and the timing of the assessment of pain was not performed during the peak of the analgesic response or functional activities. Therefore, the present study aims to assess the effects of TENS on measures of pain, function, and descending inhibition using the maximal tolerable intensity of TENS in participants with LBP.

METHODS/DESIGN

This study will be a randomized crossover trial. The participants for this study will be recruited from various places, including the University of Hartford, physical therapy clinics, and local businesses in the Hartford area, as well as online websites geared towards clinical trial recruitment. A total of 34 participants will receive all three treatments: active TENS, placebo TENS, and no treatment control. The treatment order will be randomized using a website-based randomization tool. For active TENS, a modulating frequency of 2-125 Hz will be applied with a variable pulse duration and maximal tolerable intensity for 30 min. The TENS will be left on for post-treatment testing to assess the effects during its maximally effective period for a total of 50 to 60 min. Furthermore, the intensity may be turned down if muscle twitching is present to ensure blinding of the evaluator. For placebo TENS, the unit will deliver current for 45 s, ramping to 0 in the last 15 s. The primary outcome will be pain intensity at rest and with movement, determined using the numerical pain rating scale. The secondary outcomes will be pressure pain threshold, heat pain threshold, temporal summation of pain, conditioned pain modulation, sit-to-stand test, and repeated trunk flexion. The assessments will be performed immediately before and after treatment. Statistical analysis of the data obtained will consider a significance level of p < 0.05.

DISCUSSION

This study will provide evidence concerning the effects and mechanisms of TENS treatment in participants with chronic non-specific low back pain. The outcomes, including pain, function, and descending inhibition, will help us gain a greater understanding of how TENS can be used for these participants.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05812885. Registered on 24th May 2023.

Chronic pain and local pain in usually painless conditions including neuroma may be due to compressive proximal neural lesion

It has been unexplained why chronic pain does not invariably accompany chronic pain-prone disorders. This question-driven, hypothesis-based article suggests that the reason may be varying occurrence of concomitant peripheral compressive proximal neural lesion (cPNL), e.g., radiculopathy and entrapment plexopathies. Transition of acute to chronic pain may involve development or aggravation of cPNL. Nociceptive hypersensitivity induced and/or maintained by cPNL may be responsible for all types of general chronic pain as well as for pain in isolated tissue conditions that are usually painless, e.g., neuroma, scar, and Dupuytren's fibromatosis. Compressive PNL induces focal neuroinflammation, which can maintain dorsal root ganglion neuron (DRGn) hyperexcitability (i.e., peripheral sensitization) and thus fuel central sensitization (i.e., hyperexcitability of central nociceptive pathways) and a vicious cycle of chronic pain. DRGn hyperexcitability and cPNL may reciprocally maintain each other, because cPNL can result from reflexive myospasm-induced myofascial tension, muscle weakness, and consequent muscle imbalance- and/or pain-provoked compensatory overuse. Because of pain and motor fiber damage, cPNL can worsen the causative musculoskeletal dysfunction, which further accounts for the reciprocity between the latter two factors. Sensitization increases nerve vulnerability and thus catalyzes this cycle. Because of these mechanisms and relatively greater number of neurons involved, cPNL is more likely to maintain DRGn hyperexcitability in comparison to distal neural and non-neural lesions. Compressive PNL is associated with restricted neural mobility. Intermittent (dynamic) nature of cPNL may be essential in chronic pain, because healed (i.e., fibrotic) lesions are physiologically silent and, consequently, cannot provide nociceptive input. Not all patients may be equally susceptible to develop cPNL, because occurrence of cPNL may vary as vary patients' predisposition to musculoskeletal impairment. Sensitization is accompanied by pressure pain threshold decrease and consequent mechanical allodynia and hyperalgesia, which can cause unusual local pain via natural pressure exerted by space occupying lesions or by their examination. Worsening of local pain is similarly explainable. Neuroma pain may be due to cPNL-induced axonal mechanical sensitivity and hypersensitivity of the nociceptive nervi nervorum of the nerve trunk and its stump. Intermittence and symptomatic complexity of cPNL may be the cause of frequent misdiagnosis of chronic pain.

Reply to Jensen, O.K. On the Use of Quantitative Sensory Testing to Estimate Central Sensitization in Humans. Comment on "Schuttert et al. The Definition, Assessment, and Prevalence of (Human Assumed) Central Sensitisation in Patients with Chronic Low Back Pain: A Systematic Review. J. Clin. Med. 2021, 10, 5931"

We thank Dr. Jensen for his interest [...].