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

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High-voltage pulsed radiofrequency to treat secondary glossopharyngeal neuralgia

Radiofrequenza pulsata ad alto voltaggio per trattare
una nevralgia glossofaringea secondaria
Clinical report
Pathos 2020, 27; 2. Online 2020, Jun 30
Carmelo Costa,1 Francesco Inserra,2 Filippo Indelicato 3
1Pain Therapy, Humanitas Istituto Clinico Catanese, Catania (Italy)
2Neurosurgery, Centro Gamma knife, AO Cannizzaro, Catania (Italy)
3Radiology, Humanitas Istituto Clinico Catanese, Catania (Italy)
Summary  Glossopharyngeal neuralgia (GN) is a quite uncommon neuropathic face pain syndrome. In the classic form pain occurs as recurring paroxysmal, unilateral, short time lasting and shooting or electric shock-like attacks in the sensory area of the ninth cranial nerve. The secondary form can be caused by surgery injuries, cancer, infections, vascular malformations or elongated styloid process (Eagle syndrome). We present the case of a patient with GN occurred eight months after stereotactic radiosurgery of acoustic neuroma. Pain was drug-resistant but responded significantly to high voltage pulsed radiofrequency CT-guided treatment. No complications were reported neither throughout the procedure nor in the immediate postoperative period.
Riassunto  La nevralgia del nervo glossofaringeo (NG) è una sindrome neuropatica dolorosa della faccia relativamente rara. Il dolore nella forma classica si presenta sotto forma di attacchi parossistici ricorrenti, unilaterali, di breve durata e di qualità lancinante o a scossa elettrica nel territorio anatomico del IX. La forma secondaria può far seguito a vari traumi chirurgici, neoplasie, infezioni, malformazioni vascolari o un processo stiloideo allungato (sindrome di Eagle). Presentiamo il caso di una paziente che ha sviluppato una NG dopo circa 8 mesi da un trattamento con radiochirurgia stereotassica per neurinoma del nervo acustico. Il dolore era resistente alla terapia farmacologica ma ha risposto in modo significativo al trattamento con radiofrequenza pulsata ad alto voltaggio, TAC guidata, senza riportare alcuna complicanza intra e postoperatoria.
Key words  Glossopharyngeal neuralgia, pain, case, drugs, mininvasive therapy, radiofrequency
Parole chiave  Nevralgia glossofaringea, dolore, caso, farmaci, terapia mininvasiva, radiofrequenza

Introduction
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.

Materials and methods
A 62 year-old woman, CM, with a 3-year history of typical trigeminal neuralgia on her left second branch (V2), started in 2016. Early on, trigeminal neuralgia was thought to be idiopathic and treated with carbamazepine (CBZ) at the dose of 400 mg/day twice a day, with good control of pain and mild and acceptable side-effects (drowsiness and dizziness).  Due to the persistent pain, that was less sensitive to CBZ  with the passing of time, the patient, after about two years from the onset of symptoms, decided autonomously to undergo NMR that detected left acoustic neuroma the size of 2,2 cm x 2,2 cm compressing the trigeminal nerve. She was first evaluated by neurosurgeon which ruled out tumor resection because it was considered dangerous, as the removal of the neuroma could have caused permanent neurological damage. Another neurosurgeon proposed stereotactic radiosurgery and the patient accepted his advise.
Clinical history
Since pain worsen and was drug poorly-controlled, on January 2019 the neurosurgeon treated  trigeminal nerve first at the root entry zone level,  with 86,7 Gy single dose (Figure 1) and 4 months later, on May, the acoustic neuroma compressing the V cranial nerve, with 22Gy single dose (Figure 2).
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).

Technique
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.

Results
During the procedure the patient remained hemodynamically stable without any episodes of bradycardia or hypotension and tolerated the procedure without pain. No complications were reported neither throughout the procedure nor in the immediate postoperative period. When the patient leaving the hospital, after about 8 hours, she still rated her intensity pain with NRS 7/8 at rest and 9/10 when swallowing. Therefore the patient continued to take pregabalin 225 mg/day in three doses. Over the next two weeks the pain was not reduced. But by the third week there was a gradual improvement (NRS 5/6) and by the forth week she was painless (NRS 0). To date, after 8 months by procedure, NRS remains 0. Dysesthesia continues in the V cranial nerve only.

Discussion
Even if NG is deemed uncommon, it is possible that it is less rare than usually believed due to both difficulties in diagnosis and unawareness of the disease.1
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
In our case report, the secondary neuropathy could be caused by stereotactic radiosurgery due to the excessive absorption of radiation by nearby locations treated with radiation therapy. Compression by neuroma was excluded due to the timing of the events. Despite radiation injury can cause secondary glossopharyngeal neuralgias, they usually occur after long time caused by fibrosis. In the scientific literature we have found no reference of early post radiation injury about IX cranial nerves. On the contrary, cranial nerves are deemed very radiation-resistant and the stereotactic radiosurgery is a treatment recommended for non-invasive therapy of NG unresponsive to medical management and without surgical indications.10
However, in order to avoid the excessive absorption of radiation by nearby nervous structures treated, the radiotherapy was planned in two phases. Preference was given to the trigeminal nerve procedure, due to sharp and uncontrolled pain felt by the patient and the acoustic neuroma treatment has been postponed for a few months because of its slow growth. It is difficult to understand which treatment may have been responsible of post radiotherapy injury on glossopharyngeal nerve.
Our diagnostic process included the performance of glossopharyngeal nerve anesthetic block4 to validate the suspected diagnosis, due to the complexity of the clinical picture. Pain and dysesthesia of two continuous nerves, V and IX cranial nerves, indeed made it difficult to understand the effective involvement of glossopharyngeal nerve. The deterioration of the clinical picture led us has shorten the time renouncing to diagnostic nervous block.
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.

Conflicts of interest
The authors certify the study was conducted without conflicts of interest.
Published
30th June 2020
Bibliografia
2) Shah RAJ, Padalia D. Glossopharyngeal neuralgia. Stat-Pearls-NCBI Bookshelf. Update 2020 March 30: 1-11.
4) Narouze SN. Interventional management of head and face pain. Springer ed. 2014: 129.
8) Raj PP, Lou L, Erdine Set al. Staats. Glossopharyngeal nerve block. In: Raj PP ed. Radiographic imaging for regional anesthesia and pain management. Philadelphia, PA: Churchill Livingstone. 2002: 56-60.

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