Case report: Peripheral nerve stimulation relieves post-traumatic trigeminal neuropathic pain and secondary hemifacial dystonia

Abstract

Post-traumatic trigeminal neuropathic pain (PTNP) combined with secondary dystonia are rare sequelae of orofacial injury and often do not respond to conservative treatment. The consensus on treatment for both symptoms is yet to be standardized. This study reports the case of a 57-year-old male patient with left orbital trauma who developed PTNP immediately after the injury and secondary hemifacial dystonia 7 months thereafter. To treat his neuropathic pain, we performed peripheral nerve stimulation (PNS) using a percutaneously implanted electrode to the ipsilateral supraorbital notch along the brow arch, which instantly resolved the patient's pain and dystonia. PTNP was relieved in a satisfactory manner until 18 months after the surgery, despite a gradual recurrence of the dystonia since 6 months after the surgery. To the best of our knowledge, this is the first reported case of PNS used for the treatment of PTNP combined with dystonia. This case report highlights the potential benefits of PNS in relieving neuropathic pain and dystonia and discusses the underlying therapeutic mechanism. Moreover, this study suggests that secondary dystonia occurs due to the uncoordinated integration of afferent sensory and efferent motor information. The findings of the present study indicate that PNS should be considered for patients with PTNP following the failure of conservative treatment. Secondary hemifacial dystonia may benefit from PNS upon further research and long-term assessment.

Keywords: neuromodulation; peripheral induced movement disorders; peripheral nerve stimulation (PNS); post-traumatic neuropathic pain; trigeminal nerve.

Figure 1

(A–C) Changes in the patient's hemifacial and cervical dystonia over time. (A) Pre-implant surgery, the dystonia on the left side of the patient's face is seen, manifesting as an involuntary contraction of the left hemifacial. (B) Satisfactory relief of the dystonia is still evident at 6 months after PNS surgery. (C) Involuntary contraction of the left-sided facial muscles reappeared at 12 months after PNS surgery. (D) Anteroposterior radiograph of the cranium demonstrating the placement of the supraorbital PNS-stimulating electrodes. (E, F) Bilateral forehead skin biopsy using immunolabeled protein gene product 9.5 demonstrating markedly lower epidermal neurite (yellow arrows) density in the left forehead (F) vs. that in the right forehead (E). PNS, peripheral nerve stimulation.

Figure 2

Illustration of the potential mechanism by which electric stimulation via PNS may simultaneously relieve neuropathic pain and dystonia in PTNP by influencing sensorimotor integration processes. (A) PTNP arises in the region of the forehead innervated by the supraorbital and supratrochlear nerves. Trigeminal sensory afferent neurons convey amplified nociceptive signals (red arrows) to the ipsilateral TSNC. Next, the cortical and subcortical structures integrate the sensory information and transmit aberrant movement signals through the facial nucleus and motor efferent neurons, though occasionally, integrated signals are projected directly from the TSNC to the facial nucleus (13) (indicated by dotted green lines). (B) PNS modulates the pain signals (blue arrows and fine red arrows) and downregulates the efferent motor information (fine green arrows). PNS, peripheral nerve stimulation; PTNP, post-traumatic trigeminal neuropathic pain; TSNC, trigeminal sensory nuclear complex.