Nervus Intermedius Neuralgia
Nervus intermedius neuralgia is an uncommon cause of primary otalgia. Also known as geniculate neuralgia, nervus intermedius neuralgia is believed to be caused by compression of the nervus intermedius portion of the cranial nerve VII (facial) by aberrant blood vessels or tumor in a manner analogous to trigeminal and glossopharyngeal neuralgia.
Although cranial nerve VII is primarily a motor nerve comprising special visceral efferent fibers that innervate the facial muscles, a small number of sensory and parasympathetic fibers are also present. These sensory fibers provide sensory innervations to the skin of the external auditory meatus, portions of the nasal and nasopharyngeal mucosa, and the anterior two-thirds of the tongue. When the nervus intermedius and its associated geniculate ganglion are infected with herpes zoster virus, a clinical syndrome known as Ramsey Hunt syndrome occurs.
The pain of nervus intermedius neuralgia is severe and is rivaled only by that of trigeminal and glossopharyngeal neuralgia and cluster headache. The pain has been described as like having an ice pick repeatedly jabbed into the ear. Uncontrolled pain of this severity has been associated with suicide and should therefore be treated as an emergency. Attacks can be triggered by daily activities involving contact with the external acoustic meatus or auricle.
Patients have also noted that attacks of nervus intermedius neuralgia can be triggered by lying on the affected side. Disorders of lacrimation, salivation, and taste have also been reported in patients suffering from nervus intermedius neuralgia.
Pain can be controlled with medication in some patients, but microvascular decompression or surgical resection of the nervus intermedius is required in approximately 50% of cases. The association between multiple sclerosis and trigeminal neuralgia does not appear to be strong in patients with nervus intermedius neuralgia, but a single case has been reported.
What are the Symptoms of Nervus Intermedius Neuralgia
Nervus intermedius neuralgia causes severe, episodic pain afflicting the area of the acoustic auditory meatus supplied by the nervus intermedius. The pain is unilateral and characterized by paroxysms of electric shock–like pain lasting from several seconds to less than 2 minutes.
The progression from onset to peak is essentially instantaneous.
Patients with nervus intermedius neuralgia go to great lengths to avoid any contact with trigger areas. In contrast, persons with other types of facial pain, such as temporomandibular joint dysfunction, tend to constantly rub the affected area or apply heat or cold to it.
Patients with uncontrolled nervus intermedius neuralgia frequently require hospitalization for rapid control of pain. Between attacks, patients are relatively pain free. A dull ache remaining after the intense pain subsides may indicate persistent compression of the nerve by a structural lesion. Disorders of lacrimation, salivation, and taste may also be present. This disease is almost never seen in persons younger than 30 years.
Patients with nervus intermedius neuralgia often have severe depression (sometimes to the point of being suicidal), with high levels of superimposed anxiety during acute attacks. Both of these problems may be exacerbated by the sleep deprivation that often accompanies painful episodes.
How is Nervus Intermedius Neuralgia diagnosed?
All patients with a new diagnosis of nervus intermedius neuralgia should undergo magnetic resonance imaging (MRI) of the brain and brainstem, with and without gadolinium contrast medium, to rule out posterior fossa or brainstem lesions and demyelinating disease.
Magnetic resonance angiography is also useful to confirm vascular compression of the nervus intermedius or geniculate ganglion by aberrant blood vessels. Functional MRI may also provide useful information as to the anatomical location of the pathophysiology responsible for the patient’s symptoms.
Additional imaging of the sinuses should be considered in the case of any question of occult or coexisting sinus disease. If the first division of the trigeminal nerve is affected, ophthalmological evaluation to measure intraocular pressure and rule out intraocular pathological conditions is indicated. Screening laboratory tests consisting of a complete blood count, erythrocyte sedimentation rate, and automated blood chemistry should be performed if the diagnosis of trigeminal neuralgia is in question. A complete blood count is required for baseline comparisons before starting treatment with carbamazepine (see discussion of treatment).
Nervus intermedius neuralgia is generally a diagnosis of exclusion, although the clinical presentation makes it a straightforward clinical diagnosis that can be made on the basis of a targeted history and physical examination. Diseases of the eyes, ears, nose, throat, and teeth may mimic nervus intermedius neuralgia or may coexist and confuse the diagnosis.
Atypical facial pain or temporomandibular joint dysfunction is sometimes confused with nervus intermedius neuralgia, but it can be distinguished by the character of the pain—atypical facial pain is dull and aching, whereas the pain of nervus intermedius neuralgia is sharp and neuritic.
Additionally, the pain of nervus intermedius neuralgia occurs in the distribution of the nervus intermedius, whereas the pain of atypical facial pain does not follow a specific nerve distribution. Multiple sclerosis should be considered in all patients who present with nervus intermedius neuralgia before the fifth decade of life.
Carbamazepine is considered first-line treatment for nervus intermedius neuralgia. In fact, a rapid response to this drug helps confirm the clinical diagnosis.
Despite the safety and efficacy of carbamazepine, some confusion and anxiety exist surrounding its use. This medication, which may be the patient’s best chance for pain control, is sometimes discontinued because of laboratory abnormalities erroneously attributed to it. Therefore baseline measurements consisting of a complete blood count, urinalysis, and automated blood chemistry profile should be obtained before starting the drug.
Carbamazepine should be initiated slowly if the pain is not out of control, with a starting dose of 100 to 200 mg at bedtime for 2 nights.
The patient should be cautioned about side effects, including dizziness, sedation, confusion, and rash. The drug is increased in 100- to 200-mg increments given in equally divided doses over 2 days, as side effects allow, until pain relief is obtained or a total dose of 1200 mg per day is reached. Careful monitoring of laboratory parameters is mandatory to avoid the rare possibility of a life-threatening blood dyscrasia. At the first sign of blood count abnormality or rash, this drug should be discontinued.
Failure to monitor patients on carbamazepine can be disastrous, because aplastic anemia can occur. When pain relief is obtained, the patient should be kept at that dosage of carbamazepine for at least 6 months before tapering of the medication is considered. The patient should be informed that under no circumstances should the drug dosage be changed or the drug refilled or discontinued without the physician’s knowledge.
In the uncommon event that carbamazepine does not adequately control a patient’s pain, gabapentin may be considered. As with carbamazepine, baseline blood tests should be obtained before starting therapy and the patient should be cautioned about potential side effects, including dizziness, sedation, confusion, and rash.
The initial dose is 300 mg at bedtime for 2 nights. The drug is then increased in 300-mg increments given in equally divided doses over 2 days, as side effects allow, until pain relief is obtained or a total dose of 2400 mg per day is reached. At this point, if the patient has experienced only partial pain relief, blood values are measured and the drug is carefully titrated upward using 100-mg tablets. Rarely is a dosage greater than 3600 mg per day required.
Pregabalin represents a reasonable alternative to gabapentin and is better tolerated in some patients. Pregabalin is started at 50 mg three times per day and may be titrated upward to 100 mg three times per day as side effects allow.
Pregabalin is excreted primarily by the kidneys, and thus the dosage should be decreased in patients with compromised renal function.
Baclofen may be of value in some patients who fail to obtain relief from carbamazepine, gabapentin, or pregabalin. As with those drugs, baseline laboratory tests should be obtained before beginning baclofen therapy and the patient should be warned about the same potential adverse effects.
Start with a 10-mg dose at bedtime for 2 nights, then increase the drug in 10-mg increments given in equally divided doses over 7 days, as side effects allow, until pain relief is obtained or a total dose of 100 mg per day is reached. This drug has significant hepatic and central nervous system side effects, including weakness and sedation. As with carbamazepine, careful monitoring of laboratory values is indicated when using baclofen.
When treating individuals with any of these drugs, the physician should make sure the patient knows that premature tapering or discontinuation of the medication may lead to the recurrence of pain, which will be more difficult to control.
Microvascular Decompression of the Nervus Intermedius and/or Geniculate Ganglion
Compression of the nervus intermedius and the geniculate ganglion by aberrant arteries can cause nervus intermedius neuralgia. Microvascular decompression of these neural structures in a manner analogous to the Janneta procedure may provide dramatic symptomatic relief.
Section of the Nervus Intermedius
This neurosurgical technique is the invasive treatment of choice for those patients with nervus intermedius neuralgia who have failed to respond to conservative pharmacological management and microvascular decompression procedures.
To perform this procedure, the nervus intermedius and geniculate ganglion are identified and isolated and the nervus intermedius is sectioned in two places.
Some surgeons also advocate extirpation of the geniculate ganglion. Section of the nervus intermedius alone provides excellent palliation of pain in 75% to 90% of cases.
The pain of nervus intermedius neuralgia is severe and can lead to suicide; therefore it must be considered a medical emergency, and strong consideration should be given to hospitalizing such patients.
If a dull ache remains between the intense paroxysms of pain, the clinician should have a high index of suspicion that the nidus of the patient’s pain is persistent compression of the nerve by a structural lesion such as a brainstem tumor or schwannoma.
Nervus intermedius neuralgia is an uncommon cause of otalgia. Because of the potential for disastrous clinical outcome should a more common cause of otic pain be overlooked (e.g., tumor or the temporal bone, brainstem, or nasopharynx), the diagnosis of nervus intermedius neuralgia must by necessity be one of exclusion.
Because of the severity of the pain associated with this syndrome, aggressive pharmacological management in an inpatient setting may be required. Surgical treatment consisting of the sectioning of the nervus intermedius is often the patient’s best option for complete and long-lasting pain relief.