WBR0426

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 43-year-old male presents to the physician’s office with complaints of an inability to differentiate between sweet and sour tastes at the tip of his tongue. Upon further questioning, the patient denies inability to swallow and reports normal sensation of food in his tongue. The physician suspects an injury of a specific cranial nerve (CN) might be causing the patient’s symptoms. Which of the following additional findings will further confirm the physician’s diagnosis?]]
Answer A	AnswerA::Inability to tolerate normal sounds
Answer A Explanation	AnswerAExp::Inability to tolerate normal sounds, or hyperacusis, may be caused by an injury to CN VII.
Answer B	AnswerB::Absence of salivation from the parotid gland
Answer B Explanation	AnswerBExp::Salivation from the parotid gland is achieved by CN IX. In converse, salivation from the submandibular and sublingual glands is provided by CN VII.
Answer C	AnswerC::Inappropriate balance
Answer C Explanation	AnswerCExp::Balance is provided by CN VIII.
Answer D	AnswerD::Absence of pupillary constriction
Answer D Explanation	AnswerDExp::Pupillary constriction is provided by CN III.
Answer E	AnswerE::Absence of cough reflex
Answer E Explanation	AnswerEExp::Cough reflex is a reflex provided by CN X.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The tongue is a complex structure that receives neural innervations from several cranial nerves (CN). The facial nerve (CN VII) is responsible for taste at the anterior 2/3 of the tongue. On the other hand, sensation in the anterior 2/3 of the tongue is provided by the mandibular branch of the trigeminal nerve (CN V3). The taste and sensation of the posterior 2/3 of the tongue is provided by the glossopharyngeal nerve (CN IX). Motor innervation of the tongue is provided by the hypoglossal nerve (CN XII). The patient in the vignette presents with symptoms of CN VII defect. CN VII innervates the stapedius muscle, the smallest skeletal muscle in the human body that is responsible of dampening vibrations of the stapes and prevents its excessive movement. Hyperacusis, the inability to tolerate normal sounds that are perceived as abnormally loud sounds, is caused by paralysis of the stapedius muscle due to CN VII injury that will cause very wide oscillation of the stapes and abnormally large reaction of the ossicles in response to normal sounds. Educational Objective: CN VII, or facial nerve, innervates the anterior 2/3 of the tongue to give normal tongue sensation in that region. It also innervates the stapedius muscle in the ear that is responsible of dampening the vibration of the stapes in the ear. Injury of CNVII will cause inability to taste from the anterior 2/3 of the tongue and hyperacusis, the inability to tolerate normal sounds. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Cranial, WBRKeyword::nerve, WBRKeyword::hyperacusis, WBRKeyword::tongue, WBRKeyword::taste
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::