In diabetes, which cranial nerve palsy can occur and present with ptosis and 'down-and-out' eye?

• A. Trochlear nerve (CN IV)
• B. Oculomotor nerve (CN III) palsy
• C. Abducens nerve (CN VI)
• D. Optic nerve (CN II)

Answer: (B)

The scenario points to an oculomotor nerve palsy from diabetic microvascular ischemia. The oculomotor nerve (cranial nerve III) controls most of the eye muscles and the levator palpebrae, so when it is affected the eye drifts outward and downward (unopposed lateral rectus and superior oblique) and the eyelid droops (ptosis). In diabetes, this palsy is often pupil-sparing because the central motor fibers are affected while the superficial parasympathetic fibers that regulate the pupil are preserved; if the pupil is involved (dilated), that would raise concern for a compressive lesion like an aneurysm and needs urgent evaluation. Other cranial nerves mentioned would produce different patterns (trochlear palsy affects eye rotation with vertical diplopia but not typically ptosis; abducens palsy causes inability to abduct; optic nerve palsy affects vision).