High-voltage pulsed radiofrequency to treat secondary glossopharyngeal neuralgia - Pathos

Glossopharyngeal neuralgia is a relatively uncommon1 neuropathic painful syndrome in the sensory area supplied by the glossopharyngeal nerve, the 9th cranial nerve. It was found that the incidence of GN is 0,7/100.000 population a year. As is typically the case with neuralgias, pain is paroxysmal, brief, unilateral, severe and is perceived as excruciating, “needle-like” or “electrical shock-like".2

Pain is precipitated  by a variety of harmless actions as swallowing, coughing, chewing, talking or yawning, real trigger actions. Pain is felt in the mandible angle, internal ear, tonsillar fossa and base of the tongue (Table 1). A classical glossopharyngeal neuralgia and a secondary type are described.3 Classical type seems caused by compression of IX cranial nerve at the ganglion level or at the root entry zone by vessels. It is characterized by typical paroxysmal short-lived pain attacks without clinically evident neurological deficit.

Secondary type can be caused by injury, often of surgical nature, neoplasm, infection, vascular malformation or elongated styloid process (Eagle’s syndrome).4

Secondary types  are characterized by constant pain in between the pain attacks and neurological deficits in the sensory area of the nerve like hypoaesthesia. If the treatment with antiepileptic or antidepressant drugs fails, surgical therapy can be performed removing the causes that produce suffering of the nerve. When the causes of GN are not detectable or removable, the continuous radiofrequency (CRF) thermoablation or pulsed radiofrequency (PRF) neuromodulation are effective and sure alternative techniques.5,6 In doubtful cases, a diagnostic block with a local anesthetic should be tried first to confirm the origin of pain.

trigeminal pain disappeared with a slow and gradual relief in the month of July, that is after 6 months from the trigeminal stereotactic radiosurgery and the patient stopped the carbamazepine. In September the patient developed hypo/dysesthesia along the left sensorial pathway of V and IX cranial nerves and in October she developed pain along the left sensorial pathway of IX cranial nerve. Pain resembling to sore throats worsened by swallow both liquid and solid foods. Moreover she developed pain that was confined to the left back of the tongue, the concha of the ear and the mastoid. The dysesthesia persisted especially in the V cranial nerve and less in the IX cranial nerve. A MRI showed stopping growth of the acoustic neuroma. She returned taking a CBZ 600 mg/day and paracetamol when needed  but with poor pain control. She rated her pain intensity on a numerical rating scale, NRS, ranging from 0 (no pain) to 10 (the worst pain possible). Her level of perceived pain intensity was 7-8 pain at rest and 9-10 when swallowing. At this time the patient was referred to our Pain Service Spoke. Patient was advised to switch  CBZ to pregabalin 150 mg/day taken in two doses. A glossopharyngeal diagnostic nerve block, at the styloid process level, was planned to ascertain actual involvement of IX cranial nerve in the source of pain. But patient’s quality of life, who couldn’t eat anymore due to severe pain caused by swallowing, worsened quickly. Pregabalin was increased to 225 mg/day taken in three doses but the pain was not alleviated. Therefore it was decided, with informed consent of the patient, to performed glossopharyngeal neuromodulation pulsed radiofrequency, under CT-guidance at the styloid process level (Figure 3).

The procedure was performed in November 2019, as agreed. Patient was placed supine with her head turns slightly to the right (about 30° degrees) and CT scanning was used to determine the appropriate puncture approach and the corresponding skin insertion point to reach the left styloid process. Vital parameters, electrocardiography, heart rate and oxygen saturation were recorded in continuous mode and noninvasive blood pressure was recorded at 5 minutes interval. Intravenous (IV) access was obtained and mild sedation with IV midazolam 2 mg was given. The Anesthesiologist checked sedation and vital parameters. After sterilization,6 the insertion point, detected trough the CT, was anesthetized with 1% lidocaine. Next a 22-gauge, 100 mm length, 5 mm active tip radiofrequency needle, provided with thermocouple built-in, connected to radiofrequency device, was introduced under CT- guidance to make contact with the styloid process bone. The needle was then withdrawn, walked off the styloid process posteriorly and advanced another 5 mm approximately. Repeated CT scans were used to confirm that the needle tip was localized to the medial edge of the styloid process (Figure 4).

The impedance was 270 ohm and it was sign of correctly working of electrical circuit. Sensory stimulation of up to 0,5 Volt at 50 Hz was performed and the carefully advance of the needle was stopped immediately when a provoked concordant pain was reported in the back of the tongue, tonsils and pharynx. Motor stimulation was performed subsequently up to 1 V at 2 Hz and contractions of the muscles innervated by the spinal accessory nerve were absent. The motor stimulation only reproduced local muscular contractions. The patient only felt slightly contractions of tongue. Aspiration from the needle was negative for blood and fluid. Pulsed radiofrequency was performed with progressively increasing the voltage 65 V to 100 V7 for 360 sec. The radiofrequency device automatically allows to increase the voltage without increase temperature at the same time, which does not exceed 42°C.

Besides, due to both anatomically proximity with V cranial nerve and resemblance with NT symptoms, it is often misdiagnosed in favor of most common NT. Sometimes the two neuralgias can occur simultaneously in the same patient.8 The same argument, even more so, applies to secondary glossopharyngeal neuralgias, in which continuous pain, that can occur in chronic tonsillitis or oropharyngeal carcinoma, common diseases, may be a clinical presentation of neuropathy more than nociceptive pain in the nervous anatomical site.9

Finally, to performed the procedure we chose more peripheral approach, posteriorly to styloid process considered to be easier and safer than that performed to Andersh’s ganglion at foramen jugular level. The CT-guided instead of fluoroscopic view has helped to increase accuracy to achieve anatomic target.

The neuromodulation, as frequently happens, causes onset of pain relief later than neuroablative techniques11 and, after 4 weeks from treatment,  its full effects have been accomplished. On the other hand, neither early nor late complications have been reported, and the procedure has proved to be painless also at high voltage. This allowed do not inject, before performing PRF, any local anesthetic and in an area highly crowded of important vascular and nervous structures, is certainly an advantage.

8 months after treatment, the patient still maintains pain relief without taking analgesic drugs. It is not excluded, if yet disputed, that both the increase of the electric field achieved by increasing the voltage over the 45 V,12 and the exposure time duration beyond 120 sec,13 maintaining a constant temperature not exceeding the 42°C, can contribute to improve the outcome.

Although it is only a case report, our experience highlights susceptibility of glossopharyngeal nerve to injuries of various kinds, although mild injuries, and the effectiveness of extra cranial minimally invasive treatment with pulsed radiofrequency.