16.2.3 Other Neuromodulation

Non-invasive vagal stimulation showed reduction of allodynia in a rodent model of trigeminal neuropathic pain [50], but to date, there are no published clinical trials in humans. By contrast, invasive vagal stimulation for epilepsy is rarely associated with the development of trigeminal nerve pain [51]. No trials or case series have been published on the use of sphenopalatine ganglion stimulation despite its efficacy in cluster headache. A beneficial effect on painful trigeminal neuropathy from occipital stimulation has been anecdotally reported [47, 52]. Although transcutaneous nerve stimulation has been used for neuropathic pain in general, no systematic studies have appeared in literature supporting its use, and in the authors’ experience, any limited effectiveness is offset by the unpleasantness of the need to apply the electrodes on the skin of the face. While acupuncture for trigeminal nerve pain is widely practised in many countries, a review of ten clinical trials, all published in Chinese, was criticized for poor methodological quality [53].

16.3 Discussion

Several neuromodulation methods ranging from non-invasive applications to those requiring major surgery have been described for the treatment of painful trigeminal neuropathy—less so for trigeminal neuralgia. In special circumstances, for example, recurrent trigeminal neuralgia after neuroablative procedures or microvascular decompression, or in patients with inoperable middle or posterior fossa tumour or MS, they may offer a reasonable option [46]. Problematically, to date, all evidence for the efficacy of neuromodulation in trigeminal nerve pain comes from low-quality studies, that is, mostly retrospective small case series. Nevertheless, years of experience involving patients with disabling facial pain refractory to other treatments should not be discounted. Mini-invasive neuromodulation (peripheral nerve and trigeminal ganglion stimulation) appears to provide similar long-term pain relief as invasive central neuromodulation with lesser risk and may therefore be considered as a preferential treatment in trigeminal neuropathy. In disabled patients who fail to respond to this treatment, invasive central neuromodulation (DBS, MCS) remains an option. Non-invasive interventions (TMS, tDCS) show short-term effectiveness but long-term data are virtually non-existent and therefore they should be offered only as part of a research study.

For peripheral neuromodulation, technological advances may facilitate adoption of new methods more widely than to date. Miniature-sized electrodes implanted percutaneously next to a nerve under ultrasound control will simplify surgery. Wireless systems have been developed to obviate the need for implantable IPGs. Non-invasive methods similarly are undergoing development; high-definition tDCS systems designed for home use with internet-based feedback controls will drastically reduce visits to the clinic. Whether or not these new methods become mainstream must, however, be based on outcomes from adequately powered controlled studies designed for well-defined craniofacial pain conditions.