The Clinical Syndrome
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 ( Fig. 18.1 ). 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 (see Chapter 14 ).
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 ( Fig. 18.2 ). 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.
Signs and Symptoms
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.
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 ( Fig. 18.3 ). 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 ( Fig. 18.4 ). 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).