Trigeminal neuropathy: Two case reports of gasserian ganglion stimulation

Abstract This report describes the successful treatment of two patients with trigeminal neuropathy by using gasserian ganglion stimulation. Case reports: The first case report deals with a 53‐year‐old woman suffering from right‐sided facial pain after a gamma knife lesion for schwannoma of the right inner ear. For 9 years, several interventions with the aim of relieving the pain were unsuccessful; in fact, they had aggravated the symptoms. A trial with a neurostimulator at the level of the Gasser ganglion had an immediately positive effect on her score for facial pain, which decreased from 7.3 to 0 on a visual analog scale, assessed during a period of 2 months. Additionally, the patient had weaned off all her medication by the end of the period. The second case report describes a 64‐year‐old man suffering from trigeminal neuropathy, which mainly manifested itself as an itch. For a period of 15 years, neither medication nor several interventions were effective. A trial with an electrode at the level of the Gasser ganglion reduced his pain score from 7.0 to 1.5 on a visual analog scale, assessed during a period of three months. His medication could be limited to pregabalin 150 mg bidaily. In contrast, prior to the implantation, his oral medication consisted of pregabalin 75 mg up to five times a day. Conclusion: These case reports show that stimulation of the gasserian ganglion is a successful, minimally invasive, and non‐destructive treatment in refractory trigeminal neuropathy and should be considered earlier in the treatment algorithm of trigeminal neuropathy.

Headache Society. Both classifications are shown in Table 1. Following the classification of the International Headache Society, trigeminal neuropathy usually has a cause, which can be a traumatic event, such as a mechanical, chemical, thermal lesion or radiation. It can be secondary to a postherpetic infection (Olesen, 2018 abnormalities. Trigeminal neuralgia is described as a paroxysmal pain, abrupt in onset and termination. It is perceived as an electric shock-like pain.
Our first case study concerns a patient suffering from trigeminal neuropathy caused by a gamma knife lesion, which manifests itself as a painful, tingling, and cold sensation. In our second case study, trigeminal neuropathy manifests itself as an itching sensation. Itching is defined as an uncomfortable sensation causing a desire to scratch.
Itching becomes chronic if it persists after 6 weeks (Yosipovitch et al., 2018). Itch-sensitive neurons can be divided into two subtypes: histaminergic neurons and non-histaminergic neurons. Histaminergic neurons are activated in acute itching, and chronic itching is not induced by histamine (Yosipovitch et al., 2018). Chronic itching has well-recognized similarities with neuropathic pain also known as neuropathic itching. The same neuromediators are found in chronic itching and chronic pain including substance P, opioids, nerve growth factor, neurotrophin 4, and proteases (Yosipovitch et al., 2007).  (Haviv et al., 2014).

CURRENT TREATMENT STRATEGIES
In case of a trigeminal neuropathy which manifests as an itch, no specific antipruritic drugs have been developed. Due to the similarities with chronic pain, antidepressants and anticonvulsants are also administered for inhibition of itching. Topical agents such as capsaicin, aspirin, and salicylates are used for more localized chronic itching. Oral cyclooxygenase inhibitors do not ameliorate pruritus (Yosipovitch et al., 2007). Immunosuppressants, such as thalidomide and methotrexate, are used for dermatological diseases, but potentially have severe side effects with long-term use (Yosipovitch et al., 2018).
Invasive procedures, such as microvascular decompression (MVD), radiofrequency ablations, and gamma knife procedures are proven not to be effective in patients with trigeminal neuropathy. Moreover, in 73% of the patients symptoms are worsening (Mehrkens & Steude, 2007;Sweet, 1988). Neuromodulation techniques such as motor cortex stimulation and deep brain stimulation targeting subcortical regions have possible severe complications such as seizures, deep electrode infection leading to sepsis, ventricular hemorrhage and is therefore not recommended (Antony et al., 2019).
Neuromodulation at the level of the gasserian ganglion has been used successfully in the treatment of neuropathic facial pain and is appropriate in patients with trigeminal neuropathy, i.e. a lesion of the trigeminal nerve, iatrogenic or from another cause (Mehrkens & Steude, 2007). Due to the overlap between chronic pain and chronic itching, neuromodulation could have a positive effect in these patients, as stimulation of glycinergic dorsal horn neurons alleviates pain perception (Foster et al., 2015).
This case report describes the use of neurostimulation of the gasserian ganglion in two patients with a trigeminal neuropathy for whom all previous therapies have failed.

FIRST CASE
A Under local anesthesia, the electrode was successfully covered by marsupialization. Ten days after this procedure, she reported a pain score of 0/10 and did no longer take any medication.

SECOND CASE
A 64-year-old man suffered from trigeminal neuropathy, which mainly manifested as an itch near the right eyebrow and on the right nostril.
This resulted in scratching during his sleep, causing ulcers on the right nostril (ala nasi) and the right eyebrow ( Figure 4). Otherwise, he had no significant medical history. In the past, he only had an episode of atrial fibrillation, for which nebivolol and acetylsalicylic acid had been prescribed.
Since 1980, the patient had trigeminus neuralgia in the second branch of the trigeminal nerve. An alcoholization of the infraorbital nerve was performed, which reduced the complaints. Since he suffered from recurrent pain, an MVD was performed with favorable results lasting for 10 years. After 10 years the pain reappeared, but a

A B
F I G U R E 2 Skull-base X-ray of the first case (a) anteroposterior view, (b) lateral view. Visualization of the tripolar electrode placed through the foramen ovale. The electrode is tunneled subcutaneously along the neck to the right infraclavicular fossa was implanted at a second stage also in the infraclavicular fossa on the right and connected to the electrode. A skull-based X-ray was obtained.
Three months after the procedure, the patient's VAS score had dropped to 1.5/10. The patient rated his PGIC as very satisfied. He reported some minor tingling's during nighttime. His oral medication was adjusted to pregabalin 150 mg bidaily. In contrast, prior to the implantation, his oral medication consisted of pregabalin 75 mg up to five times a day. In the following months, the dose of oral medication was further reduced to pregabalin 75 mg in the morning and 150 mg in the evening; though, an attempt to reduce pregabalin even further was unsuccessful. This can be explained by the fact that the neurostimulator was accidentally turned off at the time of the second follow-up at the pain center. Ten months after implantation, the VAS pain score remained 1.8/10 and the patient was satisfied. One and a half year after implantation, the patient was still on the same dose of pregabalin with a pain score of 2/10 and was satisfied with the therapy. Although the itchiness was mainly resolved, the scratching had become an unconscious habit over the years. Consequently, the scratch marks had not disappeared but improved. No adverse events were noted. Besides, the study of Kustermans et al. (2017), including 17 patients, demonstrates that this technique gives at least 50% pain relief in 44% of patients on a long-term basis. This percentage is higher compared to other surgical techniques (Kustermans et al. 2017).

DISCUSSION
The dorsal root ganglion is responsible for the transmission of signals from the peripheral to the central nervous system and is involved in the control over nociceptive signals, as described in the gate control theory of pain by Melzack and Wall (Foster et al., 2015). by the international headache society (Deer et al., 2014). This recommendation is primarily based on a study issued by Taub et al. in 1997(Taub et al., 1997. In our patients, we use a more advanced technique.

CONCLUSION
These case reports show that stimulation of the gasserian ganglion is a successful, minimally invasive, and non-destructive treatment in refractory trigeminal neuropathy and should be considered earlier in the treatment algorithm of trigeminal neuropathy.

FUNDING INFORMATION
No funding was received for this work.