Human Studies

To determine whether patients with painful myofascial temporomandibular disorders (TMD) demonstrate facilitated temporal summation (TS) responses to painful heat stimuli applied to the painful trigeminal and extratrigeminal regions and whether there is a side difference in the trigeminal region for myofascial TMD pain patients compared to healthy controls.

Diabetes mellitus (DM) is a global challenge with many diverse health sequelae, of which diabetic peripheral neuropathy (DPN) is one of the most common. A substantial number of patients with DPN develop chronic pain, but the genetic and epigenetic factors that predispose DPN patients to develop neuropathic pain are poorly understood. Recent targeted genetic studies have identified mutations in α-subunits of voltage-gated sodium channels (Navs) in patients with painful DPN. Mutations in proteins that regulate trafficking or functional properties of Navs could expand the spectrum of patients with Nav-related peripheral neuropathies. The auxiliary sodium channel β-subunits (β1-4) have been reported to increase current density, alter inactivation kinetics, and modulate subcellular localization of Nav. Mutations in β-subunits have been associated with several diseases, including epilepsy, cancer, and diseases of the cardiac conducting system. However, mutations in β-subunits have never been shown previously to contribute to neuropathic pain. We report here a patient with painful DPN and negative genetic screening for mutations in SCN9A, SCN10A, and SCN11A-genes encoding sodium channel α-subunit that have been previously linked to the development of neuropathic pain. Genetic analysis revealed an aspartic acid to asparagine mutation, D109N, in the β2 subunit. Functional analysis using current-clamp revealed that the β2-D109N rendered dorsal root ganglion neurons hyperexcitable, especially in response to repetitive stimulation. Underlying the hyperexcitability induced by the β2 subunit mutation, as evidenced by voltage clamp analysis, we found a depolarizing shift in the voltage-dependence of Nav1.7 fast-inactivation and reduced use-dependent inhibition of the Nav1.7 channel.

The ACCURATE randomized, controlled trial compared outcomes of dorsal root ganglion (DRG) stimulation versus tonic spinal cord stimulation (SCS) in 152 subjects with chronic lower extremity pain due to complex regional pain syndrome (CRPS) type I or II. This ACCURATE sub-study was designed to evaluate whether therapy habituation occurs with DRG stimulation as compared to SCS through 12-months. A modified intention-to-treat analysis was performed to assess percentage pain relief (PPR) and responder rates at follow-up visits (end-of-trial, 1, 3, 6, 9, 12-months post-permanent implant) for all subjects that completed trial stimulation (DRG:N=73, SCS_N=72). For both groups, mean PPR was significantly greater at end-of-trial (DRG:82.2%, SCS:77.0%) than all other follow-ups. Following permanent DRG system implantation, none of the time points were significantly different from one another in PPR (range:69.3-73.9%). For the SCS group, PPR at 9-months (58.3%) and 12-months (57.9%) was significantly less than at 1-month (66.9%). The responder rate also decreased for the SCS group from 1-month (68.1%) to 12-months (61.1%). After stratifying by diagnosis, it was found that only the CRPS-I population had diminishing pain relief with SCS. DRG stimulation resulted in more stable pain relief through 12-months, while tonic SCS demonstrated therapy habituation at 9- and 12-months. Trial Registration: The ACCURATE study was registered at ClinicalTrials.gov with Identifier NCT01923285. Perspective: This article reports on an ACCURATE sub-study, which found that long-term therapy habituation occurred at 12-months with SCS, but not DRG stimulation, in patients with CRPS. The underlying mechanisms of action for these results remain unclear, although several lines of inquiry are proposed.