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Difficulty: HardPhysical Examination Findings

A 71-year-old man with a history of poorly controlled hypertension and type 2 diabetes mellitus is evaluated in the emergency department for severe, continuous vertigo, nausea, and vomiting that began abruptly 5 hours ago. He is unable to walk unassisted due to profound unsteadiness. He reports no hearing changes, tinnitus, or recent illnesses. Blood pressure is 174/98 mm Hg.

On physical examination, the patient is in visible distress and keeps his eyes closed to minimize the spinning sensation. When his eyes are open, a spontaneous, horizontal nystagmus is observed. The nystagmus changes direction, beating to the left on leftward gaze and to the right on rightward gaze. A head impulse test is performed; as the physician rapidly turns the patient's head to either side, the patient's eyes remain steadily fixed on the physician's nose without requiring a corrective saccade. An alternating cover test demonstrates a slight vertical shift of the eyes as they uncover.

Which of the following is the most likely underlying mechanism for this patient's physical examination findings?

  1. A
    Viral inflammation of the vestibular nerve
  2. B
    Migration of calcium debris into the semicircular canals
  3. Acute ischemia in the vertebrobasilar territoryAnswer
  4. D
    Impaired resorption of endolymphatic fluid
  5. E
    Purulent inflammation of the membranous labyrinth

Answer

The correct answer is acute ischemia in the vertebrobasilar territory.
This patient is presenting with acute vestibular syndrome (continuous vertigo lasting greater than 24 hours). The physical examination uses the HINTS exam (Head Impulse, Nystagmus, Test of Skew) to differentiate between peripheral causes (like vestibular neuritis) and central causes (like a posterior circulation stroke). This patient displays all three classic central findings: a normal head impulse test (intact vestibulo-ocular reflex), direction-changing nystagmus (peripheral nystagmus is unidirectional), and a vertical skew deviation. In an elderly patient with cardiovascular risk factors, these findings are highly specific for acute ischemia in the vertebrobasilar territory (cerebellar or brainstem infarction).

Step-by-Step Solution

1
Analyze the patient's presenting symptoms and risk factors.
The patient has acute vestibular syndrome (AVS), characterized by rapid onset of continuous vertigo, nausea, vomiting, and gait instability. He also has significant vascular risk factors (hypertension, diabetes).
Establishing the syndrome (AVS) directs the physical examination to differentiate between peripheral and central causes of the vertigo.
2
Evaluate the head impulse test findings.
The head impulse test is normal, meaning the patient's eyes remain fixed on the target without a corrective saccade when the head is rapidly turned.
In the setting of AVS, an abnormal head impulse test typically points to a peripheral cause (e.g., vestibular neuritis) because the vestibulo-ocular reflex arc is damaged. A normal test strongly implies that the peripheral vestibular apparatus is intact, pointing toward a central etiology.
3
Assess the nystagmus and alternating cover test findings.
The patient exhibits direction-changing gaze-evoked nystagmus and vertical skew deviation on the cover test.
Both direction-changing nystagmus and vertical skew deviation are highly specific signs of central vestibular dysfunction, typically localized to the brainstem or cerebellum.
4
Synthesize the findings to determine the underlying pathophysiology.
The combination of a normal head impulse test, direction-changing nystagmus, and vertical skew deviation confirms a central nervous system etiology. Given the acute onset and vascular risk factors, this represents an ischemic stroke in the posterior circulation.
These three findings constitute the HINTS exam, which is more sensitive than early MRI for detecting acute stroke in the vertebrobasilar territory.

Key Concept

The HINTS exam (Head Impulse, Nystagmus, Test of Skew) is critical in evaluating patients with acute vestibular syndrome. Any of the central signs (normal head impulse test, direction-changing nystagmus, or vertical skew deviation) strongly suggests a central etiology, such as an ischemic stroke in the posterior circulation.
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Physical Examination Findings

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