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Zorluk: ZorPhysical Examination Findings

A 58-year-old man with a history of poorly controlled hypertension and type 2 diabetes mellitus presents to the clinic with an acute onset of double vision. He awoke with these symptoms this morning and notes a mild, aching pain behind his right eye. Neurological examination reveals complete ptosis of the right upper eyelid. When the examiner manually elevates the right eyelid, the right eye is resting in a downward and outward (abducted) position. The right pupil is 3 mm and briskly reactive to light; the left pupil is also 3 mm and reactive. The left eye has a full range of extraocular movements.

The physician suspects an ischemic microvascular etiology causing an isolated cranial mononeuropathy. To definitively assess whether the trochlear nerve (CN IV) remains intact on the affected side—differentiating an isolated palsy from a more extensive orbital apex or cavernous sinus process—the physician should ask the patient to attempt which movement, and observe for which specific ocular response?

  1. A
    Attempt to look medially and observe for failure of the eye to cross the midline
  2. Attempt to look downward and observe for intorsion of the eyeCevap
  3. C
    Attempt to look downward and medially and observe for depression of the eye
  4. D
    Attempt to look upward and observe for extorsion of the eye
  5. E
    Attempt to look laterally and observe for complete abduction of the eye

Cevap

The correct approach is to ask the patient to attempt to look downward and observe for intorsion of the eye.
The correct answer demonstrates how to adapt a physical examination maneuver to test the trochlear nerve (CN IV) in the setting of a complete CN III palsy. The superior oblique muscle, innervated by CN IV, has three primary actions: intorsion, depression, and abduction. In a structurally normal eye, its action as a depressor is best isolated by asking the patient to look downward and inward (adduct). However, in a patient with a CN III palsy, the medial rectus is paralyzed, making adduction impossible. Because the resting position of the eye is abducted (due to the intact lateral rectus), the superior oblique is mechanically disadvantaged as a depressor but is positioned optimally as an intorter. Therefore, asking the patient to attempt to look downward will stimulate the superior oblique, resulting in observable intorsion (internal rotation) of the eye, which can be visualized by watching the conjunctival blood vessels rotate. This finding confirms that CN IV is intact.

Adım Adım Çözüm

1
Identify the primary cranial nerve deficit based on the physical exam findings.
The patient has a pupil-sparing right oculomotor nerve (CN III) palsy.
Ptosis, a 'down and out' resting eye position, and a normal, reactive pupil are classic signs of an ischemic CN III palsy.
2
Determine the anatomical goal of the required physical examination maneuver.
The goal is to isolate and test the function of the trochlear nerve (CN IV), which innervates the superior oblique muscle.
Confirming that CN IV is intact helps differentiate an isolated CN III mononeuropathy from a multi-cranial nerve syndrome (e.g., cavernous sinus pathology).
3
Adapt the standard physical exam maneuver to the patient's existing mechanical constraints.
Because the medial rectus (CN III) is paralyzed, the eye cannot be adducted. Instead, asking the patient to look downward while the eye remains abducted maximizes the intorsion action of the superior oblique.
The superior oblique acts primarily as a depressor when the eye is adducted, but acts as a pure intorter when the eye is abducted.

Anahtar Kavram

In the setting of a complete CN III palsy, the standard test for CN IV (looking down and in) is impossible due to medial rectus paralysis; CN IV must instead be tested by looking for intorsion when the patient attempts to look downward.
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Physical Examination Findings

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