A 45 years old male patient complaints of double vision when walking upstairs. His past history is significant for Type-ll diabetes, well controlled with glyburide. The nerve most probably involved is
**Core Concept**
The patient's complaint of double vision when walking upstairs suggests a problem with the cranial nerves responsible for eye movements, particularly the cranial nerves that control vertical gaze. The condition is likely related to the patient's history of Type-2 diabetes, which can cause damage to the peripheral nerves (diabetic neuropathy) or the nerves within the brain (cerebellar or brainstem lesions).
**Why the Correct Answer is Right**
The patient's symptoms are consistent with a lesion affecting the oculomotor nerve (cranial nerve III), which controls the majority of eye movements, including vertical gaze. The oculomotor nerve is responsible for innervating the extraocular muscles that control eye movements, including the superior rectus, inferior rectus, medial rectus, and inferior oblique muscles. Damage to the oculomotor nerve can cause weakness or paralysis of these muscles, leading to double vision and other eye movement abnormalities. In patients with Type-2 diabetes, diabetic neuropathy can cause damage to the oculomotor nerve, leading to the patient's symptoms.
**Why Each Wrong Option is Incorrect**
* **Option A:** The trochlear nerve (cranial nerve IV) is responsible for innervating the superior oblique muscle, which controls intorsion and depression of the eye. Damage to the trochlear nerve would not cause double vision when walking upstairs.
* **Option B:** The abducens nerve (cranial nerve VI) is responsible for innervating the lateral rectus muscle, which controls abduction of the eye. Damage to the abducens nerve would cause lateral rectus palsy, not double vision.
* **Option D:** The trigeminal nerve (cranial nerve V) is responsible for sensation in the face and motor control of the muscles of mastication. Damage to the trigeminal nerve would not cause double vision.
**Clinical Pearl / High-Yield Fact**
In patients with diabetes, it's essential to consider diabetic neuropathy as a cause of cranial nerve palsies, particularly oculomotor nerve palsy. This condition can be a presenting feature of diabetic neuropathy, and prompt recognition and treatment can help prevent further complications.
**Correct Answer:** C.