Neuromodulation of the central nervous system for facial pain

Chronic craniofacial pain can lead to significant morbidity and reduced quality-of-life. Refractory pain subsequently leads to maladaptive changes within the central nervous system (CNS). It is logical to consider modulation of implicated neural networks to mitigate or reverse these changes in order to alleviate suffering. In this report, we reviewed the current literature in neuromodulation of CNS in facial pain treatment. We conducted PRISMA-compliant systematic review using MEDLINE and EMBASE databases. We included studies applying stimulation to the CNS to treat facial pain. Demographic data, design, duration, participants, clinical details, outcomes, adverse effects were extracted. Out of 1005 unique publications, 57 were included for analysis. Main techniques included were transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation (rTMS), motor cortex stimulation (MCS), deep brain stimulation (DBS), and spinal cord stimulation (SCS). For tDCS, rTMS, and MCS, the main stimulation target was primary motor cortex; while several different DBS targets (e.g., thalamic nuclei, anterior cingulate cortex, periaqueductal grey matter) were studied. While most studies showed improvement in Numeric Rating Scale for pain, values range widely from 11.1% in one MCS study to 90% in one rTMS study, with majority within 20-60%. There is heterogeneity across research designs, including patient selection, outcome measures, and follow-up. Standardized reporting framework is required to allow direct comparison between different modalities within subgroups of facial pain patients.