Perspective

Trigeminal neuralgia, or tic douloureux, is a syndrome featuring painful paroxysms in one or more distributions of the trigeminal nerve. Trigeminal neuralgia is relatively uncommon, with an annual incidence of 4 to 13 cases per 100,000 population.1,2 It is more common in women than in men, with a female-to-male ratio of 1.7 : 1. Affected persons typically are between 50 and 69 years of age, and symptoms occur more frequently on the right side of the face.³

Pathophysiology

Trigeminal neuralgia is an idiopathic disorder, although significant evidence points to vascular compression of the trigeminal nerve root in many cases. This compression commonly is caused by a tortuous arterial or venous loop in the posterior fossa, an arteriovenous malformation, or rarely a tumor. In surgical case series, vascular compression of the trigeminal nerve root is found in 80 to 90% of cases.4,5 Of note, however, structural lesions are not found in all patients with trigeminal neuralgia.⁶

Clinical Features

Trigeminal neuralgia is manifested with unilateral facial pain, typically characterized as lancinating paroxysms of pain in the lips, teeth, gums, or chin. The pain of trigeminal neuralgia is commonly associated with physical triggers such as chewing, brushing the teeth, shaving, washing or touching the affected area of the face, swallowing, or exposure to hot or cold temperature in the affected area. The maxillary and mandibular divisions of the trigeminal nerve are most commonly involved; rarely, the ophthalmic division alone is involved. Patients tend to experience the pain in clustered episodes that last a few seconds to several minutes. The attacks can occur during the day or night but rarely arise during sleep.6,7

Diagnostic Strategies

A careful history and physical examination should be performed to rule out other painful facial conditions, including odontogenic infections, sinus disease, otitis media, acute glaucoma, temporomandibular joint disease, and herpes zoster. Patients who lack local pathologic findings to explain the painful syndrome require a careful neurologic examination. The presence of a neurologic deficit should prompt suspicion of a structural lesion, such as aneurysm, tumor, or other intracranial lesion (e.g., from multiple sclerosis). Of note, 2 to 4% of patients with trigeminal neuralgia also have multiple sclerosis.⁸ Patients with normal findings on the head and neck examination and no neurologic deficits who have episodic, unilateral facial pain associated with nonpainful triggers are likely to have trigeminal neuralgia.

Management

Since the 1960s the treatment of choice for trigeminal neuralgia has been the anticonvulsant medication carbamazepine. The purported effectiveness of this treatment, however, is based on uncontrolled studies, and the mechanism of action of anticonvulsant therapy for trigeminal neuralgia is unclear. The true efficacy of medical therapy is difficult to assess owing to a high rate of spontaneous remission. Nonetheless, carbamazepine appears to be an effective and well-tolerated agent for treatment of trigeminal neuralgia. The initial dosage of carbamazepine is 100 mg twice daily; this dose is then increased to three times daily after 1 week. The dose may be increased by 100 mg/day, up to a maximum of 1200 mg/day. A complete blood count and liver function studies are performed periodically in patients who are taking carbamazepine to monitor for hematologic and hepatic side effects. Additional agents that have been used for treatment of trigeminal neuralgia include phenytoin, baclofen, valproate sodium, lamotrigine, gabapentin, and levetiracetam. None of these drugs has been shown to be more effective than carbamazepine.⁷

Surgical management has been a therapeutic option since the 1950s. Surgical procedures include both peripheral and central procedures. Peripheral strategies include medication injection and cryotherapy techniques designed to temporarily block or permanently ablate branches of the peripheral trigeminal nerve. Although these procedures are relatively effective initially, recurrence is common. Repeated nerve blocks are not recommended because of a high risk of permanent facial anesthesia.

Central procedures can be divided into percutaneous approaches and open approaches. Percutaneous destruction of the trigeminal ganglion can be done by means of radiofrequency ablation, thermal ablation, glycerol injection, or balloon microcompression. These procedures carry the risk of corneal anesthesia, oculomotor paresis, or masticatory weakness.⁹

Open surgical management is the surgical option of choice in many treatment centers. Open surgical procedures include microvascular decompression of the nerve with or without partial ablation. Although the open microvascular decompression procedure has proved to be effective, with pain relief achieved in 80 to 95% of patients, the surgery is associated with the risk of significant complications, including hearing loss, facial anesthesia, cerebrospinal fluid (CSF) leak, brainstem or cerebellar injury, headaches, meningitis, and death.10,11 Gamma Knife radiosurgery, a minimally invasive, precision-directed stereotactic radiosurgery, also has been associated with good outcomes. This highly specialized technique requires extremely sophisticated stereotactic radiofrequency equipment and is available only in specialized centers, but in many cases it has similar results for pain relief without the morbidity associated with open procedures in patients who might otherwise be a surgical risk.^12–14

Disposition

Patients with suspected trigeminal neuralgia should be referred for specialty evaluation. Patients with a neurologic deficit require urgent imaging studies, typically magnetic resonance imaging (MRI), to rule out a mass or vascular abnormality.

Perspective

The acute onset of facial nerve paralysis often will prompt an ED visit. Fortunately, early diagnosis and therapy may improve the patient’s chance for recovery of function of the facial nerve. Facial nerve paralysis of acute onset affects approximately 20 to 25 persons per 100,000 population per year, without geographic, gender, or race predilection.15,16

Principles of Disease

The facial nerve innervates the muscles of facial expression and the muscles of the scalp and external ear in addition to the buccinator, platysma, stapedius, stylohyoid, and posterior belly of the digastric muscles. The sensory portion of the nerve supplies the anterior two thirds of the tongue with taste and sensation to portions of the external auditory meatus, soft palate, and adjacent pharynx. The parasympathetic portion supplies secretomotor fibers for the submandibular, sublingual, lacrimal, nasal, and palatine glands.¹⁷

The nerve originates from the pontomedullary junction of the brainstem and enters the internal auditory meatus with cranial nerve VIII. Within the temporal bone, the facial nerve has four major branches: the greater and lesser superficial petrosal nerves, the nerve to the stapedius muscle, and the chorda tympani. The facial nerve exits the temporal bone at the stylomastoid foramen and then enters the parotid gland, where it divides to supply the muscles of facial expression.17,18

Pathophysiology

The three main causes of facial nerve paralysis that are relevant to emergency medicine are grouped into infectious, traumatic, and neoplastic.

Trauma

In patients with head trauma, the facial nerve is the most commonly injured cranial nerve. The cause generally is a temporal bone fracture with nerve transection. Surgical exploration is warranted if there is firm evidence that the nerve has been transected, indicated by a sudden onset of complete unilateral facial paralysis, loss of electrical activity, and evidence of a displaced fracture involving the facial canal.

Neoplasm

Tumors of the facial nerve itself or tumors anywhere along the course of the facial nerve that invade or compress the nerve may lead to facial paralysis. The course is typically progressive for at least 3 weeks. A sudden onset of paralysis, however, does not rule out an underlying tumor because facial paralysis secondary to a neoplasm is of sudden onset in approximately 25% of cases.³⁸ A neoplastic cause should be suspected in patients who suffer from recurrent ipsilateral facial paralysis, significant pain, prolonged symptoms, or any other concomitant cranial nerve abnormality.

Clinical Features and Differential Considerations

The medical history in patients with facial paralysis focuses on onset of the paralysis, concentrating on timing and rapidity of onset and associated signs and symptoms. A rapid onset of facial paralysis with dysgeusia and hyperacusis preceded by a viral prodrome is suggestive of Bell’s palsy. A history of recurrent ipsilateral paralysis or slow progression of symptoms is more characteristic of a tumor. Associated cranial nerve abnormalities, although occasionally seen with Bell’s palsy, also point to the possibility of a tumor or ischemic insult. The Ramsay Hunt syndrome causes significant pain and a vesicular rash, although the rash may follow the facial paresis by a few days. Significant anatomic abnormalities on visual or otoscopic inspection of the ipsilateral ear will be found with bacterial otitis media and otitis externa. Finally, systemic symptoms or bilateral facial paresis, especially in endemic areas, should raise the possibility of Lyme disease.

Diagnostic Strategies

The diagnostic workup of acute facial nerve paresis is based on whether the clinical picture is suggestive of a disease process other than Bell’s palsy. If the clinical history is classic for Bell’s palsy, no imaging or laboratory studies are required. Of note, any history of possible exposure warrants serologic evaluation for Lyme disease. Although outpatient testing including electroneurography may ultimately be performed, this usually is not part of the initial evaluation.

The presence of a “central” seventh nerve paralysis (upper face sparing) should prompt imaging with computed tomography (CT) or MRI, and consideration should be given to the possibility of an acute stroke or other hemispheric lesion. History or physical examination findings suggestive of a possible tumor require imaging to rule out a neoplasm. The study of choice will depend on the institution and preferences of the consultant.

Disposition

Most patients who have a seventh nerve paralysis will have a clinical diagnosis of Bell’s palsy and may be discharged with referral for short-term follow-up. Patients with a possible hemispheric process, such as stroke or tumor, require further evaluation and usually hospitalization. Patients thought to have Lyme disease require immediate initiation of appropriate antibiotic therapy.

In patients with a peripheral facial nerve paralysis, the ipsilateral eye should be patched, and consideration should be given to ophthalmologic follow-up because there is a high rate of corneal abrasions and corneal dryness associated with the inability to blink properly or to close the eye completely.

Perspective

Vestibular schwannoma, formally referred to as acoustic neuroma, is a rare but important cause of sensorineural hearing loss. The annual incidence of vestibular schwannoma is 1 case per 100,000 population, with a mean age at the time of detection of 46 to 58 years.³⁹ The female-to-male ratio is 1.5 : 1. Vestibular schwannoma is rarely bilateral, occurring in this form in approximately 5% of cases and generally associated with type 2 neurofibromatosis. Although histologically benign, vestibular schwannoma can cause neurologic damage by direct compression on the eighth cranial nerve and the other structures in the cerebellopontine angle.⁴⁰

Principles of Disease

Vestibular schwannoma arises from the Schwann cells covering the vestibular branch of the eighth cranial nerve as it passes through the internal auditory canal. The tumor may compress the cochlear (acoustic) branch of the eighth cranial nerve, causing hearing loss, tinnitus, and dysequilibrium. Continued growth of the tumor may result in compression of structures in the cerebellopontine angle, where the facial and trigeminal nerves may be compressed and damaged. Larger tumors may further encroach on the brainstem and if large enough may compress the fourth ventricle, ultimately resulting in signs of increased intracranial pressure (ICP).⁴¹

Clinical Features

Asymmetrical sensorineural hearing loss is the hallmark of vestibular schwannoma. Up to 15% of patients with this tumor, however, will have normal results on audiometry. These patients typically have symptoms such as unilateral tinnitus, imbalance, headache, fullness in the ear, otalgia, and facial nerve weakness. Thus, patients with asymmetrical symptoms should be further evaluated for vestibular schwannoma even with normal findings on audiometry.⁴²

Vestibular schwannomas are extremely slow-growing tumors, averaging an approximately 1-mm increase per year, although many do not grow at all on serial examinations.⁴³ Symptom onset is therefore generally gradual. In one series of 126 cases, the average time from symptom onset to discovery of a vestibular schwannoma was approximately 4 years.⁴⁴

Diagnostic Strategies

When vestibular schwannoma is suspected, the patient is evaluated by audiometry or gadolinium-enhanced MRI. This imaging technique is extremely sensitive and has led to earlier diagnosis and a decrease in mean size at detection of vestibular schwannoma. CT lacks the necessary sensitivity in the posterior cranial fossa to reliably rule out the presence of vestibular schwannoma. The smaller the tumor at the time of diagnosis, the more options there are for therapy and the better the potential prognosis.⁴⁰

Differential Considerations

A majority of disease entities included in the differential diagnosis for vestibular schwannoma cause symmetrical sensorineural hearing loss. Asymmetrical sensorineural hearing loss has few causes other than vestibular schwannoma. Ménière’s disease may present a diagnostic dilemma because it can be asymmetrical. Ménière’s disease may be differentiated from vestibular schwannoma in that the tinnitus of Ménière’s disease usually is intermittent, whereas the tinnitus of vestibular schwannoma typically is continuous. In addition, patients with Ménière’s disease typically describe true vertigo, whereas patients with a vestibular schwannoma are more likely to describe imbalance or dysequilibrium.

Vestibular schwannomas account for 80% of all cerebellopontine angle tumors. Among all other lesions, meningioma is the most common. Meningiomas more frequently cause symptoms of facial palsy or trigeminal nerve abnormality. Of note, however, considerable similarity between the clinical picture of a meningioma and that of vestibular schwannoma in the cerebellopontine angle has been described.⁴⁵

Management

Vestibular schwannoma may be removed surgically or ablated with stereotactic radiation therapy. In general, tumors larger than 3 cm are recommended for microsurgery because radiation treatments, such as with the Gamma Knife or linear accelerator, are less effective for local control and growth arrest in larger masses. Smaller tumors are amenable to use of stereotactic radiation therapy, which has greater salvage rates of facial nerve function and hearing.46,47 Stereotactic radiation therapy generally has good long-term outcomes of local growth arrest, with nerve salvage approaching 90% or greater. Injuries to the trigeminal, facial, and acoustic nerves and to the cerebellum are possible complications of both procedures. In patients who are minimally symptomatic with small tumors, serial monitoring with MRI is a viable nonsurgical option. All patients should be evaluated by a specialist in the evaluation and treatment of vestibular schwannoma because smaller tumor size at detection is associated with a better long-term outcome.^39,43

Disposition

Patients with suspected acoustic neuroma should be referred for audiometry or MRI and evaluation by a specialist in either otolaryngology or neurosurgery.

Perspective

Cranial mononeuropathies occur uncommonly, usually are a complication of diabetes, and most often affect the extraocular muscles. The oculomotor nerve is most commonly affected, followed in order by the trochlear and abducens nerves. In one large series in Japan, the incidence of cranial nerve palsies was 1.0% among diabetics and 0.1% among nondiabetics.48,49 Whereas ophthalmoplegia appears to be closely related to diabetes, facial palsy is less strongly correlated with this disease.^48,50

Principles of Disease

The pathologic basis of diabetic mononeuropathy appears to be ischemia of the affected cranial nerve caused by occlusion of an intraneural nutrient artery serving the nerve. This occlusion leads to injury located primarily in the center of the nerve because the core fibers are more dependent on the supply from such nutrient arteries. The peripheral fibers are less affected because they also are supplied by collateral vessels. In the oculomotor nerve, the preservation of the circumferentially located parasympathetic fibers explains the pupillary sparing that usually is found in this syndrome. In two studies, the microvascular changes in the intraneural arteries that lead to occlusion were noted in diabetic patients but absent in nondiabetics.51,52

Clinical Features

Patients typically describe acute onset of unilateral retro-ocular and supraorbital pain, diplopia, and ptosis.⁴⁹ The physical manifestations of a third cranial nerve palsy include the inability to move the eye superiorly and medially, accompanied by ptosis. The pupillary light reflex usually is present. Although it is a less common finding, the fourth and sixth cranial nerves may be affected. Patients with a fourth cranial nerve palsy are unable to move the eye inferolaterally, and those with a sixth cranial nerve palsy are unable to move the eye laterally. Because of the long intracranial course of the sixth nerve, a patient with an isolated sixth nerve palsy should be evaluated for an intracranial lesion or increased ICP.⁵³