IX Glossopharyngeal Nerve CASE HISTORY Allen is a 43-year-old construction worker. While he was eating dinner, Allen developed pain in the left side of his throat. The pain was short, brief, and stabbing in nature and only occurred when he swallowed. Allen was eating ﬁsh at the time and assumed that a ﬁsh bone was lodged in his throat. He went to the emergency department and was assessed by an otolaryngologist, but nothing was found. It was assumed that a ﬁsh bone had scratched Allen’s throat and that his symptoms would soon resolve. A month later, Allen’s pain was still present; in fact, it had increased. The pain occurred not only when he swallowed but also when he spoke and coughed. Again, while eating din- ner, Allen experienced the same pain with swallowing. He got up from the table, but after a few steps he collapsed unconscious to the ﬂoor. Although Allen quickly regained consciousness, he was immediately taken to the emergency department where he was put on a heart rate and blood pressure monitor to evaluate the function of his cardiovascular system. While he was on the monitor, the emer- gency room physician noticed an interesting correlation. Whenever Allen swallowed, he had a paroxysm (a sudden recurrence or intensiﬁcation of symptoms) of pain followed invariably within 3 to 4 seconds by a decrease in heart rate (bradycardia) and a fall in blood pressure (hypotension). Allen was examined by a neurologist who noticed no evidence of reduced perception of pharyngeal pinprick or touch, or of pharyngeal motility. A diagnosis of glossopharyngeal neuralgia was made. Allen was treated with carbamazepine. His attacks of pain stopped and his cardiovascular function returned to normal. ANATOMY OF THE GLOSSOPHARYNGEAL NERVE The name of the glossopharyngeal nerve indicates its distribution (ie, to the glossus [tongue] and to the pharynx). Cranial nerve IX emerges from the medulla of the brain stem as the most rostral of a series of rootlets that emerge between the olive and the inferior cerebellar peduncle. The nerve leaves the cranial fossa through the jugu- lar foramen along with cranial nerves X and XI (Figure IX–1). Two ganglia are situated on the nerve as it traverses the jugular foramen, the superior and inferior (petrosal) glossopharyngeal ganglia. The superior ganglion is small, has no branches, and is usually thought of as part of the inferior glossopharyngeal ganglion. The ganglia are composed of nerve cell bodies of sensory components of the nerve (Figure IX–2).164
176 Cranial Nerves CASE HISTORY GUIDING QUESTIONS 1. What is glossopharyngeal neuralgia? 2. What is the cause of glossopharyngeal neuralgia? 3. What is allodynia? 4. Why did swallowing cause Allen pain? 5. Why did Allen collapse on the ﬂoor? 6. Why was carbamazepine used to treat Allen? 7. What is the gag reﬂex, and why don’t we gag every time a bolus of food passes through the pharynx? 1. What is glossopharyngeal neuralgia? Glossopharyngeal neuralgia* is characterized by severe, sharp, lancinating pain in the region of the tonsil, radiating to the ear. It is similar to trigeminal neuralgia (see Chapter V) in its timing and its ability to be triggered by various stimuli. For exam- ple, pain may be initiated by yawning, swallowing, or contact with food in the ton- silar region. In rare instances, the pain may be associated with syncope (a fall in heart rate and blood pressure resulting in fainting). 2. What is the cause of glossopharyngeal neuralgia? Typically, glossopharyngeal neuralgia is idiopathic; that is, no cause can be identi- ﬁed. Occasionally glossopharyngeal neuralgia is secondary to the compression of cranial nerve IX by carotid aneurysms, oropharyngeal malignancies, peritonsillar infections, or lesions at the base of the skull. 3. What is allodynia? Allodynia is pain that results from a touch stimulus that normally would not cause pain. The pain is usually burning or lancinating in quality. 4. Why did swallowing cause Allen pain? Sensory nerve endings in the mucosa of Allen’s pharynx were stimulated by the pas- sage of a bolus of food and by the movements of the underlying muscles involved *Some authors use the term vagoglossopharyngeal neuralgia or glossopharyngeal and vagal neuralgia, instead of glossopharyngeal neuralgia, implying that the pain can radiate into the distribution of the vagus nerve as well as that of the glossopharyngeal nerve. However, the original term, glossopharyngeal neuralgia, is recognized by most neurologists and is more commonly used.
Glossopharyngeal Nerve 177in swallowing, coughing, and speaking. These usually harmless stimuli set off a bar-rage of pain impulses within the nervous system.5. Why did Allen collapse on the ﬂoor?Allen collapsed on the ﬂoor because his blood pressure dropped so low that he couldnot maintain adequate blood ﬂow to his brain. The mechanism for Allen’s fall inblood pressure and heart rate is not well understood. One hypothesis is that whenthe pain is most intense, general sensory impulses from the pharynx stimulate thenucleus of the tractus solitarius, which, in turn, stimulates vagal nuclei. Impulsesfrom the parasympathetic component of the vagus nerve act to slow the heart rateand decrease blood pressure. Alternatively, the rapidly ﬁring general sensory afferents may, through ephaptictransmission,* give rise to action potentials in the visceral afferent axons from thecarotid sinus as they travel together in the main trunk of the glossopharyngeal nerve.The carotid nerve would then falsley report increased blood pressure, causing areﬂexive decrease in heart rate and blood pressure via connections in the brain stem.6. Why was carbamazepine used to treat Allen?Carbamazepine is a sodium channel blocking drug that is used to treat a wide rangeof conditions from seizures to neuropathic pain. Carbamazepine reduces the neu-ron’s ability to ﬁre trains of action potentials at high frequency and therefore short-ens the duration of the paroxysm and frequently abolishes the attacks.7. What is the gag reﬂex, and why don’t we gag every time a bolus of food passes through the pharynx?The gag is a protective reﬂex that prevents the entry of foreign objects into the ali-mentary and respiratory passages. A touch stimulus to the back of the tongue orpharyngeal walls elicits the gag (see Clinical Testing). Since the passage of a bolusof food through the pharynx stimulates the tongue and pharyngeal walls, we haveto ask why swallowing does not elicit a gag reﬂex. Although the exact mechanism is not well understood, it is generally acceptedthat when a swallowing sequence is initiated, probably by signals from the cerebralcortex to swallowing center(s) in the brain stem, simultaneous inhibitory signals aresent to the gag center in the brain stem to turn off the gag reﬂex.*Ephaptic transmission occurs when a rapidly ﬁring nerve changes the ionic environment ofadjacent nerves sufﬁciently to give rise to action potentials in them. These “artiﬁcial synapses”often result from a breakdown in myelin.
Glossopharyngeal Nerve 179 The sensitivity of the gag reﬂex can be affected by cortical events. It can be sup-pressed almost completely or enhanced such that even brushing the teeth or thesight of a dental impression tray can lead to gagging. CLINICAL TESTINGAlthough cranial nerve IX comprises general sensory and motor, visceral sensory andmotor, and special sensory components, from a practical point of view only the gen-eral sensory component is tested at the bedside. Clinically, cranial nerves IX and Xare assessed by testing the gag reﬂex. The gag reﬂex involves both cranial nerves—theglossopharyngeal being the sensory afferent input and the vagus carrying the motorefferents. When assessing the gag reﬂex, right and left sides of the pharynx should belightly touched with a tongue depressor (Figure IX–13). The sensory limb of the reﬂexis considered to be intact if the pharyngeal wall can be seen to contract after each sidehas been touched. (See also Cranial Nerves Examination on CD-ROM.)Figure IX–13 Testing the gag reflex by lightly touching the wall of the pharynx. ADDITIONAL RESOURCESBrodal A. Neurological anatomy in relation to clinical medicine. 3rd ed. New York: Oxford University Press; 1981. p.460–4, 467.Ceylan S, Karakus A, Duru S, et al. Glossopharyngeal neuralgia: a study of 6 cases. Neurosurg Rev 1997;20(3):1996–2000.Dalessio DJ. Diagnosis and treatment of cranial neuralgias. Med Clin North Am 1991;75(3):605–15.Dubner R, Sessle BJ, Storey AT. The neural basis of oral and facial function. New York: Plenum Press; 1978. p. 370–2.Eyzaguirre C, Abudara V. Carotid body glomus cells; chemical secretion and transmission (modulation?) across cell-nerve ending junctions. Respir Physiol 1999;115:135–49.
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