192 CRANIAL NERVE DISORDERS
Harrison’s Manual of Medicine
CRANIAL NERVE DISORDERS
Olfactory Nerve (I)
Trigeminal Nerve (V)
Facial Nerve (VII)
Glossopharyngeal Nerve (IX)
Vagus Nerve (X)
Hypoglossal Nerve (XII)
Multiple Cranial Nerve Palsies
Disorders of vision and ocular movement are discussed in Chap. 10 and Chap. 48; dizziness and vertigo in Chap. 9; and disorders of hearing in Chap. 49;
OLFACTORY NERVE (I)
The sense of smell may be impaired by (1) interference with access of odorant to olfactory neuroepithelium (transport loss), e.g., by swollen nasal mucous membrane in URI, allergic rhinitis, or structural changes in nasal cavity such as with a deviated septum, nasal polyps, or neoplasm; (2) injury to receptor region (sensory loss), e.g., destruction of olfactory neuroepithelium by viral infections, neoplasms, inhalation of toxic chemicals, or radiation to head; and (3) damage to central olfactory pathways (neural loss), e.g., by head trauma with or without fractures of cribriform plate, neoplasms of anterior cranial fossa, neurosurgical procedures, neurotoxic drugs, or congenital disorders such as Kallmann’s syndrome.
TRIGEMINAL NERVE (V) (See Fig. 192-1)
FIGURE 192-1. The three major sensory divisions of the trigeminal nerve consist of the ophthalmic, maxillary, and mandibular nerves.
Trigeminal Neuralgia (Tic Douloureux) Frequent, excruciating paroxysms of pain in lips, gums, cheek, or chin (rarely in ophthalmic division of fifth nerve) lasting seconds to minutes. Appears in middle or old age. Pain is often stimulated at trigger points. Sensory deficit cannot be demonstrated. Must be distinguished from other forms of facial pain arising from diseases of jaw, teeth, or sinuses. Tic is rarely caused by herpes zoster or a tumor. Onset in young adulthood raises the possibility of multiple sclerosis.
Carbamazepine is effective in 75% of cases. Begin at 100 mg single daily dose taken with food and advance by 100 mg every 1–2 days until substantial (50%) pain relief occurs. Most pts require 200 mg qid; doses >1200 mg daily usually provide no additional benefit. Follow CBC for rare complication of aplastic anemia. For nonresponders, phenytoin (300–400 mg qd) or baclofen (5–20 mg tid-qid) can be tried. When medications fail, surgical gangliolysis or suboccipital craniectomy for decompression of trigeminal nerve are options; in some centers, microvascular decompression is recommended if a tortuous or redundant blood vessel is found in the posterior fossa near the trigeminal nerve.
Trigeminal Neuropathy Usually presents as facial sensory loss or weakness of jaw muscles. Causes are varied (Table 192-1) including tumors of middle cranial fossa or trigeminal nerve, metastases to base of skull, or lesions in cavernous sinus (affecting first and second divisions of fifth nerve) or superior orbital fissure (affecting first division of fifth nerve).
Table 192-1 Trigeminal Nerve Disorders
FACIAL NERVE (VII)
Lesions of the seventh nerve or nucleus produce hemifacial weakness that includes muscles of forehead and orbicularis oculi; if lesion is in middle ear portion, taste is lost over the anterior two-thirds of tongue and there may be hyperacusis; if lesion is at internal auditory meatus, there may be involvement of auditory and vestibular nerves, whereas pontine lesions usually affect abducens nerve and often corticospinal tract as well. Peripheral nerve lesions with incomplete recovery may result in diffuse continuous contraction of affected facial muscles +/– associated movements (synkinesis) of other facial muscle groups and facial spasms.
Bell’s Palsy Most common form of idiopathic facial paralysis, found in 23/100,000 annually, or 1 in 60–70 persons over a lifetime. Pathogenesis uncertain, but an association with herpes simplex virus type 1 has been documented. Weakness evolves over 12–48 h, sometimes preceded by retroaural pain. Fully 80% recover within several weeks or months.
Involves protection of eye with paper tape to depress the upper eyelid during sleep. Prednisone (60–80 mg qd over 5 d, tapered off over the next 5 d) when started early appears to shorten the recovery period and modestly improve functional outcome. In one study, treatment within 3 days of onset with both prednisone and acyclovir (400 mg five times daily for 10 d) improved outcome.
Other Facial Nerve Disorders Ramsay Hunt Syndrome is caused by herpes zoster infection of geniculate ganglion; distinguished from Bell’s palsy by a vesicular eruption in pharynx, external auditory canal, and other parts of the cranial integument. Acoustic neuromas often compress the seventh nerve. Pontine tumors or infarcts may cause a lower motor neuron facial weakness. Bilateral facial diplegia may appear in Guillain-Barré syndrome, sarcoidosis, Lyme disease, and leprosy. Hemifacial spasm may result from Bell’s palsy, irritative lesions (e.g., acoustic neuroma, basilar artery aneurysm, or aberrant vessel compressing the nerve) or as an idiopathic disorder. Blepharospasm consists of involuntary recurrent spasms of both eyelids, usually occurring in the elderly and sometimes with associated facial spasm. May subside spontaneously. Severe cases of hemifacial spasm or blepharospasm can be treated by local injection of botulinus toxin into the orbicularis oculi; spasms are relieved for 3–4 months, and injections can be repeated.
GLOSSOPHARYNGEAL NERVE (IX)
Glossopharyngeal Neuralgia Paroxysmal, intense pain in tonsillar fossa of throat that may be precipitated by swallowing. There is no demonstrable sensory or motor deficit. Other diseases affecting this nerve include herpes zoster or compressive neuropathy due to tumor or aneurysm in region of jugular foramen (when associated with vagus and accessory nerve palsies).
Carbamazepine or phenytoin is often effective, but surgical division of the ninth nerve near the medulla is sometimes necessary.
VAGUS NERVE (X)
Lesions of vagus nerve cause symptoms of dysphagia and dysphonia. Unilateral lesions produce drooping of soft palate, loss of gag reflex, and “curtain movement” of lateral wall of pharynx with hoarse, nasal voice. Diseases that may involve the vagus include diphtheria (toxin), neoplastic and infectious processes of the meninges, tumors and vascular lesions in the medulla, or compression of the recurrent laryngeal nerve by intrathoracic processes.
HYPOGLOSSAL NERVE (XII)
The twelfth cranial nerve supplies the ipsilateral muscles of the tongue. Atrophy and fasciculations of the tongue develop weeks to months after interruption of the nerve. Lesions affecting the motor nucleus may occur in the brainstem (tumor, poliomyelitis, or motor neuron disease), during the course of the nerve in the posterior fossa (platybasia, Paget’s disease), or in the hypoglossal canal.
MULTIPLE CRANIAL NERVE PALSIES
The main clinical problem is to determine whether the process is within the brainstem or outside it. Lesions that lie on the surface of the brainstem tend to involve adjacent cranial nerves in succession with only late and slight involvement of long sensory and motor pathways within the brainstem. The opposite is true of processes within the brainstem. Involvement of multiple cranial nerves outside of the brainstem may be due to diabetes, trauma, infectious and noninfectious causes of meningitis; granulomatous diseases including sarcoidosis, tuberculosis, and Wegener’s granulomatosis; tumors; and enlarging saccular aneurysms. A purely motor disorder raises a question of myasthenia gravis. Facial diplegia is common in Guillain-Barré syndrome. Ophthalmoplegia may occur with Guillain-Barré syndrome (Fisher variant) or Wernicke’s disease. Involvement of the cavernous sinus (Fig. 192-2) may be due to infection, aneurysm, a carotid-cavernous fistula, nasopharyngeal carcinoma, or a granulomatous disease. Finally, an idiopathic multiple cranial nerve disorder may occur, consisting of boring unilateral or bilateral facial pain followed by paralysis of motor cranial nerves; inflammation of the dura mater may be visualized by MRI, and treatment is with glucocorticoids.
FIGURE 192-2. Anatomy of the cavernous sinus in coronal section, illustrating the location of the cranial nerves in relation to the vascular sinus, internal carotid artery (which loops anteriorly to the section), and surrounding structures.
For a more detailed discussion, see Beal MF, Hauser SL: Common Disorders of the Cranial Nerves, Chap. 367, p. 2421, in HPIM-15.