USMLE® Step 1 Question of the Day: Dizziness Episodes
Published on Nov 24, 2021. Updated on Nov 18, 2021.
A 60-year-old woman comes to the clinic complaining of episodes of dizziness for the past month. The patient reports that the dizziness usually occurs when she gets up from bed, gets up from a seated position, or turns her head, and it lasts for approximately 30 seconds. During these episodes, she feels as though the room is spinning around her, which is accompanied by nausea. Medical history is significant for hypertension, which is treated with hydrochlorothiazide. Vital signs are within normal limits. Physical examination shows right-beating and torsional nystagmus. Hearing is intact, and the rest of the physical examination shows no abnormalities. Which of the following is most likely responsible for this patient's presentation?
A. Depletion of body fluids
B. Arterial insufficiency
C. Inflammation of the vestibulocochlear nerve (CN VIII)
D. Debris within the semicircular canal
E. Excessive build-up of the endolymph fluidScroll down to find the answer!
The correct answer to today's USMLE® Step 1 Question is...
D. Debris within the semicircular canalBefore we get to the Main Explanation, let's look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanationsThe incorrect answers to today's USMLE® Step 1 Question are...
A. Depletion of body fluids
Incorrect: This answer choice refers to orthostatic hypotension, which is diagnosed when a person's blood pressure falls upon standing or sitting. Although hydrochlorothiazide use does increase the risk for orthostatic hypotension, this phenomenon would not cause nystagmus or vertigo.
B. Arterial insufficiency
Incorrect: Rotational vertebral artery syndrome refers to a phenomenon of symptomatic posterior circulation ischemia from the compression of the vertebral arteries by bony elements of the spine (usually at CI-C2) which occurs upon head rotation. Patients may present with recurrent syncope, vertigo, nystagmus, ataxia, diplopia, nausea, dysarthria, or dysphagia. Although some of this patient’s symptoms overlap with rotational vertebral artery syndrome, standing would not cause the symptoms.
C. Inflammation of the vestibulocochlear nerve (CN VIII)Incorrect: Inflammation of the eighth cranial nerve causes vestibular neuritis or labyrinthitis. It is thought to be a viral or post-viral inflammatory disorder which leads to inflammation of the vestibular portion of the nerve. Patients often present with severe vertigo and possibly hearing loss and tinnitus. It typically occurs as an acute attack that lasts for days. This patient’s presentation and duration of symptoms favor another diagnosis.
E. Excessive build-up of the endolymph fluidIncorrect: Excessive build-up of the endolymph fluid, also known as endolymphatic hydrops, describes the hypothesis behind Ménière disease. The condition is characterized by episodic vertigo, tinnitus, and hearing loss. It is thought to occur due to an abnormality in the flow of endolymph or in the resorption of endolymph. The increased volume of the endolymph can lead to damage of the cochlea and the vestibular system of the inner ear. This patient’s presentation and intact hearing favor another diagnosis.
This patient, who presents with isolated complaints of vertigo that occurs mainly with head rotation and position changes, most likely has benign paroxysmal positional vertigo (BPPV). The diagnosis of BPPV can be confirmed by the Dix-Hallpike maneuver, in which the physician extends the patient's neck and turns it to one side while the patient is sitting, followed by rapidly placing them in a supine position so that their head hangs over the edge of the bed. On a positive test there will be nystagmus or vertigo.
BPPV is one of the most common causes of peripheral vertigo; it is characterized by episodes of spinning sensation provoked by head rotation and position changes which last approximately 30 seconds. The condition is attributed to calcium debris within the semicircular canals, known as canalithiasis. This debris likely represents loose calcium carbonate crystals originating from the utricular sac. Under normal conditions, the semicircular canals detect angular head accelerations. Debris accumulation in the canal causes inappropriate movement of the endolymph with linear accelerations, creating a false sensation of spinning when the head shifts. While symptoms can be disabling, the disorder typically responds to treatment with particle-repositioning maneuvers (Epley maneuver) in the office upon diagnosis.
Benign paroxysmal positional vertigo (BPPV) refers to episodic vertigo sensation caused by calcium debris within the semicircular canals. Episodes are typically provoked by head rotation and position changes. In contrast to other causes of vertigo, hearing and other neurologic symptoms are not seen.
Kim JS, Zee DS. Clinical practice. Benign paroxysmal positional vertigo. N Engl J Med. 2014;370(12):1138-1147. doi:10.1056/NEJMcp1309481
Coelho DH, Lalwani AK. Medical management of Ménière's disease. Laryngoscope. 2008;118(6):1099-1108. doi:10.1097/MLG.0b013e31816927f0
Dabus G, Gerstle RJ, Parsons M, et al. Rotational vertebrobasilar insufficiency due to dynamic compression of the dominant vertebral artery by the thyroid cartilage and occlusion of the contralateral vertebral artery at C1-2 level. J Neuroimaging. 2008;18(2):184-187. doi:10.1111/j.1552-6569.2007.00177.x
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