Glossopharyngeal Neuralgia

Etiology

Essential or idiopathic glossopharyngeal neuralgia is where etiology is unknown.[4][5]

Secondary causes of glossopharyngeal neuralgia include:

• Vascular compression, mainly at the nerve root: the most common cause
• Demyelinating diseases: e.g., multiple sclerosis
• Inflammatory and autoimmune diseases: e.g., Sjogren disease
• Intraoral and peritonsillar infections
• Intracranial space-occupying lesions, especially medullary tumors or tumors originating from CP angle
• Posterior fossa and cervical malformations
• Eagle syndrome or stylalgia: If the styloid process is over 25mm or the stylohyoid ligament is calcified, they can cause compression of the glossopharyngeal nerve
• Oropharyngeal cancers include carcinoma of the tongue and benign tumors like schwannomas

Epidemiology

Glossopharyngeal neuralgia is an extremely rare condition. It accounts for 0.2 to 1.3% of all types of cranial neuralgias. One long-term study of the population in Rochester, Minnesota, from 1945 to 1984 showed a crude incidence rate of 0.7 per 100000 population. The incidence was equal in both sexes. The overall rates increase with age in both males and females.[6]

In 1981 Rushton et al. published a retrospective review of the data on 217 patients with glossopharyngeal neuralgia. These patients were seen at the Mayo Clinic from the years 1922 to 1977. 57% of the cases were in patients over 50 years of age, and 43% were between 18 to 50 years of age. Approximately 74% of patients had spontaneous remissions, whereas 17% experienced no relief. Only 12% of the patients had bilateral pain.[3]

Pathophysiology

The glossopharyngeal nerve is a mixed sensorimotor nerve that exits the brainstem from the upper medulla. From that point, it leaves the skull through the jugular foramen, along with the vagus and accessory nerves. It continues its path between the internal jugular vein and the internal carotid artery as it descends and then continues beneath the styloid process. It then curves to make an arch on the side of the neck as it passes under the hyoglossus muscle to its final distribution of the base of the tongue, the palatine tonsil, and the glands of the mouth. A motor efferent supplies the stylopharyngeus muscle, which is essential in swallowing. Sensory afferents provide information from the inner surface of the tympanic membrane, the upper pharynx, as well as the posterior one-third of the tongue. Another important branch is the one to the carotid body and sinus is known as Hering's nerve. It communicates with the vagus nerve and carries information from chemoreceptors in the carotid body and baroreceptors in the carotid sinus; this is important clinically as activation of the visceral sensory branch of the glossopharyngeal neuralgia can activate the vagus nerve (tractus solitarius and dorsal motor nucleus) and produce a reflex arrhythmia. This vagal activation may explain the cardiac-related syncopal episodes sometimes associated with glossopharyngeal neuralgia.  Overall the glossopharyngeal nerve is a very small nerve that runs deep in the neck, and it is sometimes resected accidentally during open-neck dissections. For this same reason, it is often called ‘the neglected cranial nerve.’ Any infectious, inflammatory, or compressive etiologies across the glossopharyngeal nerve’s path from the end organs to the brainstem may result in hyperexcitability of the nerve and produce pain.[5][7][8]

History and Physical

The ICHD-3 provides the following diagnostic criteria for glossopharyngeal neuralgia[1]:

A. Recurrent paroxysmal painful attacks in unilateral glossopharyngeal nerve distribution and should fulfill the criterion.

B. Pain should have all the following characteristics

• Duration: Pain lasts from a few seconds to about 2 minutes
• Intensity: Severe
• Type of pain: Sharp, stabbing, shooting, or electrical shock-like sensations
• Precipitating factors: The pain is precipitated or exacerbated by coughing, yawning, swallowing, or talking

C. Pain should not be accounted for by any other ICHD-3 diagnosis.

The usual onset for glossopharyngeal neuralgia is anywhere between 21 to 75 years of age.  The incidence is most common in those of middle age. There is no sex predilection. Painful attacks may occur without any prodromal or warning symptoms. The pain occurs anywhere below the ear, in the epiglottis, palatine tonsils, the base of the tongue, and/or the posterior pharynx. Swallowing both solids and liquids can make the pain worse. The pain is aggravated by drinking both hot and cold water. The onset and resolution of pain are abrupt. Some patients experience their initial attacks as excruciating, but the pain can then become relatively mild in the chronic state. Patients usually feel no pain in between the attacks, but some can feel a residual sharp pain in between the paroxysms. In rare cases, the attacks are not transient, sharp, or stabbing painful episodes but present as a deep agonizing pain that can last for days.

The pain pattern in an individual with glossopharyngeal neuralgia is remarkably uniform. Pain episodes can occur within minutes of each other and then stop entirely for days at a time. Paroxysmal pain is felt mostly during the day, but it may wake the patient up at night. Patients with glossopharyngeal neuralgia are predisposed to lose weight from the severe pain associated with chewing and swallowing. Attacks of pain surprisingly subside on their own most of the time, but unpleasant sensations may remain for several weeks to months in the affected areas.

The physical examination of patients with glossopharyngeal neuralgia is generally benign, and the painful areas do not show any signs of sensory abnormalities for both light touch and pinprick. Sometimes glossopharyngeal neuralgia is associated with dysesthesias and/or hyperalgesia in the affected areas. If there is an absent cough or gag reflex, a detailed investigation into the etiology of the pain is necessary. In some rare cases, glossopharyngeal neuralgia and trigeminal neuralgia can occur concurrently.[1]

Evaluation

The diagnosis of glossopharyngeal neuralgia is mainly clinical and should meet all criteria as mentioned in ICHD-3. A detailed history and physical examination of the patient is therefore mandatory. A thorough ENT examination is necessary, including a throat exam and neck palpation. All the patients should have basic laboratory evaluations, including complete blood count, basic metabolic panel and erythrocyte sedimentation rate, and anti-nuclear antibodies to rule out any underlying infection, inflammation, malignancy, or temporal arteritis.

Persistent symptoms are infrequent and warrant further investigation. Complications, including syncope, should have a cardiology evaluation with an echocardiogram and Holter monitoring.

The primary role of imaging is to identify potential causes of nerve compression at the base of the skull.

Computed Tomography (CT)

CT scans do not show the nerve directly but can identify an elongated and ossified styloid process in the axial images.[9]

X-Ray

An elongated and heavily calcified styloid process can be present on the cervical spine plain radiograph on the lateral view.[9]

Magnetic Resonance Imaging (MRI)

Neurovascular compression of the glossopharyngeal nerve is most visible on MRI. Thin section T2 weighted images are ideal for seeing pathology. An MRI with contrast should be performed to see any abnormal enhancement of the nerve, vessels, or surrounding structures. The most common vascular source of nerve compression is the posterior inferior cerebellar artery (PICA). The vertebral artery and anterior inferior cerebellar artery are the second and third most common culprit vessels. The MRI can also show demyelinating brain lesions, tumors in the posterior fossa, or any malformations.

Magnetic resonance angiogram (MRA)

MRA should also be done to evaluate for a vascular loop compressing on the nerve root entry zone.[10]

Treatment / Management

Treatment/Management

Medical management: Glossopharyngeal neuralgia is usually responsive to pharmacotherapy, especially with carbamazepine or oxcarbazepine.

Carbamazepine: Starting dose 200 mg/day in a single dose (extended-release), two divided doses (immediate-release tablet), or in four divided doses (oral solution). Increase the dose gradually with increments of 200 mg/day as needed. If the dose exceeds 200mg per day, it is advisable to administer extended-release capsules in two divided doses. Maintenance dose: 400 to 800 mg daily in two divided doses (immediate-release tablet) forms) or four divided doses (oral solution); maximum dose: no more than 1,200 mg/day.

The other neuropathic pain medicines recommended by the International Association for the Study of Pain (IASP) are as below:

• Gabapentin (100 to 5000 mg/day in 1 to 4 divided doses),
• Duloxetine (20 to 90mg/day),
• Valproic acid (125-2500 mg/day in 1 to 2 divided doses),
• Clonazepam (0.5-8 mg/day),
• Lamotrigine (50 to 500 mg/day in 1 to 2 divided doses),
• Baclofen (10 to 80 mg/day in 1 to 4 divided doses),
• Phenytoin (200 to 600 mg/day in 1 to 3 divided doses),
• Pregabalin (75 to 500 mg/day in 1 to 2 divided doses) and
• Topiramate (50 to 1000 mg/day in 1 to 2 divided doses)

As a general rule, these medications should be started at low doses and titrated up as needed based on their effectiveness, tolerability, and side effects. This pain condition often shows a relapsing-remitting course, so medication can be tapered down to a low maintenance dose. Combining two or more medications with different mechanisms of action can help achieve better pain relief while avoiding side effects. A short course of opioids can be useful for intractable pain.

Adjuvant care: Cold and hot compresses, physical therapy, and psychological counseling are all options in addition to medical therapy. The success rate is variable but can be helpful.[11](B3)

Interventional Pain Management Techniques

Glossopharyngeal nerve blocks merit consideration for both diagnostic and therapeutic purposes. This block can be an option in conjunction with pharmacotherapy. A diagnostic block with a local anesthetic should be tried first to confirm the origin of the pain. If diagnostic blocks are successful, chemical neurolysis or thermal radiofrequency ablation can be performed on the nerve. Chemical neurolytic agents such as alcohol, glycerol, or phenol are typical choices. Radiofrequency ablation is typically performed at the jugular foramen to target the inferior petrous ganglion of Andersch. Accurate needle placement is critical as life-threatening bradycardia and hypotension can occur if the vagus nerve gets stimulated during the procedure. There are two common approaches to block the glossopharyngeal nerve: the intraoral and extra-oral approaches. The extra-oral technique is preferred since it is safe and easy to perform. Complications are not uncommon with glossopharyngeal neuralgia blocks. The glossopharyngeal nerve is in the vicinity of the internal jugular vein, and the carotid artery and intravascular injection can easily occur. The concomitant block of the recurrent laryngeal nerve may cause hoarseness of the voice. Always avoid bilateral glossopharyngeal nerve blocks at the same time to avoid complete vocal cord paralysis. Blockade of the vagus nerve may result in tachycardia and hypertension via blockade of parasympathetic fibers.[12][13][14](B3)

Surgical Management of Glossopharyngeal Neuralgia

Several surgical modalities are used for the treatment of glossopharyngeal neuralgia based on the etiology of the pain. The compression of the glossopharyngeal nerve by a vascular structure is the most common cause of secondary glossopharyngeal neuralgia. Microvascular decompression (MVD) of the glossopharyngeal nerve is the most widely used surgical modality to correct vascular compression of the nerve. Alternatively, a resection of the glossopharyngeal nerve alone or with branches of the vagus nerve can also be performed.

Extracranial techniques are percutaneous radiofrequency rhizotomy and direct surgical resection. These techniques are ideal in patients with essential glossopharyngeal neuralgia who failed medical management but cannot tolerate an open intracranial resection. Resection of the ipsilateral styloid process, also known as stylectomy, is a therapeutic option for Eagle syndrome. The physician must rule out other central causes of glossopharyngeal neuralgia before pursuing this surgery.

Intracranial techniques include rhizotomy or an intracranial root resection of the glossopharyngeal nerve and/or vagus nerves from its origin in the brainstem at the cerebellopontine angle. Persistent dysphagia and hoarseness of voice are the most common complications of these surgeries. Stereotactic radiosurgery with gamma knife surgery provides a less-invasive option, but data on safety and efficacy is limited.[14][15][16][17](B2)

Differential Diagnosis

• Trigeminal neuralgia: Glossopharyngeal neuralgia is most commonly mistaken for trigeminal neuralgia since both have similar pain characteristics. Additionally, both of them are cranial neuralgias with similar pathophysiology and medical management. In certain rare cases, these conditions can coexist. Since the incidence of glossopharyngeal neuralgia is 1/1000 times less than trigeminal neuralgia, underdiagnoses of glossopharyngeal neuralgia are very common; this is why a thorough history and physical examination are essential since they both differ in the location of pain and provoking factors. Pain from glossopharyngeal neuralgia occurs in the throat and tonsillar region and is exacerbated by swallowing and chewing movement, whereas pain from trigeminal neuralgia occurs on the face in the trigeminal nerve distribution and is exacerbated by a light touch on the face, washing the face and brushing the teeth.

• Jacobson’s neuralgia: When the only symptom of glossopharyngeal neuralgia is the sensory loss at the ear (the otic form of glossopharyngeal neuralgia), it gets confused with intermedius or Jacobson neuralgia.

• Temporal arteritis and temporomandibular joint dysfunction: Pain in these pathologies occurs in the same distribution, but the pain characteristics in both pathologies are entirely different from glossopharyngeal neuralgia.[5]

Prognosis

Glossopharyngeal neuralgia has a variable prognosis based on the patient’s symptoms. Most of the patients have a single episode of painful paroxysmal attacks. The annual recurrence rate is as low as 3.6%. Only 25% of patients require surgery, and the rest are manageable medically. Less than one in four patients will have bilateral pain.

Bilateral pain, multiple bouts of severe excruciating pain, and constant pain are poor prognostic indicators.[18][1]

Complications

Syncope and cardiac dysrhythmias: When the glossopharyngeal nerve gets irritated, it sends feedback via the dorsal motor nucleus of the Xth nerve. These signals also stimulate the nucleus tractus solitarius in the midbrain. Thus, during the acute glossopharyngeal neuralgia attack, abnormal stimulation produces an amplified vagal response, resulting in bradycardia, hypotension, and cardiac dysrhythmias. These autonomic changes cause cerebral hypoperfusion, slow waves on EEG, seizures, and syncope. Convulsive movements, limb clonus, automatic smacking movements of the lips, and upward turning of the eyes are signs of cerebral hypoxia.

Cardiovascular complications occur during painful episodes or immediately after the pain symptoms resolve. Management of glossopharyngeal neuralgia pain attacks with drugs and/or surgical treatment can help manage these complications. Some patients only develop cardiovascular manifestations of glossopharyngeal neuralgia without painful paroxysms, also known as non-neurologic glossopharyngeal neuralgia. These patients can receive therapy with glossopharyngeal nerve avulsion or microvascular decompression.[19][20]