Immediate Effects of External Trigeminal Nerve Stimulation on Motor Dysfunction in Parkinson's Disease

Parkinson's disease (PD), the most common movement disorder, is characterized by motor symptoms including tremor, rigidity, bradykinesia, and postural instability. These symptoms substantially impair quality of life and increase the risk of falls, disability, and accidental injury, representing a major therapeutic challenge. External trigeminal nerve stimulation (eTNS), a non-invasive neuromodulation technique, has shown promising potential in PD and other movement disorders. A clinical study published in 2017 suggested that trigeminal nerve stimulation may contribute to the alleviation of motor symptoms in patients with PD. In 2023, the U.S. Food and Drug Administration cleared the Portable Neuromodulation Stimulator (PoNS) as an adjunctive treatment for gait impairment caused by multiple sclerosis; the lingual nerve is a branch of the mandibular division of the trigeminal nerve. In the same year, experimental evidence showed that trigeminal nerve stimulation could activate intracranial dopaminergic neurons and modulate dopamine release in mice. These findings suggest substantial potential for eTNS in modulating motor dysfunction in PD, although high-level clinical evidence remains lacking. This randomized, within-subject study will evaluate the immediate effects of eTNS at different stimulation frequencies on motor dysfunction in patients with PD. Gait parameters will be quantitatively assessed using the IDEEA gait system, together with the MDS-Unified Parkinson's Disease Rating Scale Part III (MDS-UPDRS Part III), Tinetti Gait Scale, and Hoehn and Yahr Scale. This within-subject study comprises three 20-min stimulation conditions: 120-Hz eTNS, 40-Hz eTNS, and sham stimulation. Each patient with Parkinson's disease will complete all conditions in a single session in randomized order. Instrumented gait analysis, together with motor and gait rating scales, will be used to quantify immediate post-stimulation changes in gait and motor function relative to baseline.

Inclusion Criteria: 1. Patients with idiopathic Parkinson's disease diagnosed by two neurologists, according to the Chinese diagnostic criteria for Parkinson's disease formulated in 2020 by the Chinese Parkinson's Disease and Movement Disorders Society based on the MDS Clinical Diagnostic Criteria for Parkinson's disease. 2. Hoehn and Yahr stage 1-5 in the medication ON state. 3. Mini-Mental State Examination (MMSE) score \>24. 4. Stable antiparkinsonian medication for at least 1 month before the trial. 5. No history of orthopedic or musculoskeletal disorders, and no other conditions that may affect balance or gait, such as ophthalmologic disorders. 6. No history of epilepsy, intracranial tumors, or other neurological disorders; no severe psychiatric disorders, such as schizophrenia; and no long-term use of antipsychotic medications. 7. Age between 40 and 80 years. 8. Ability to cooperate with all assessments and eTNS treatment, and provision of written informed consent. Exclusion Criteria: 1. Secondary parkinsonism or atypical parkinsonian syndromes. 2. Current use of anticholinergic medications. 3. Contraindications to non-invasive electrical neuromodulation. 4. Previous eTNS treatment within the past 6 months. 5. Severe neurological, renal, cardiovascular, hepatic, or other major systemic diseases. 6. Inability to complete clinical assessments or refusal to provide written informed consent.