Clinical featues of sixth nerve palsy is –
**Core Concept**
Sixth nerve palsy, also known as abducens nerve palsy, is a condition characterized by the weakness or paralysis of the lateral rectus muscle, which is responsible for outward gaze. This results in impaired abduction of the affected eye, leading to difficulties in moving the eye laterally.
**Why the Correct Answer is Right**
The abducens nerve (CN VI) innervates the lateral rectus muscle, and its palsy leads to weakness or paralysis of this muscle. This results in the characteristic clinical features of sixth nerve palsy, including horizontal diplopia (double vision) that worsens with lateral gaze, limited or absent abduction of the affected eye, and sometimes, nystagmus (involuntary eye movements). The patient may also exhibit a head turn towards the side of the palsy to compensate for the diplopia.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because sixth nerve palsy primarily affects the lateral rectus muscle, not the medial rectus muscle, which is responsible for adduction.
**Option B:** This option is incorrect because sixth nerve palsy does not typically cause ptosis (drooping eyelid) or limited upgaze, which are more characteristic of third nerve palsy.
**Option C:** This option is incorrect because sixth nerve palsy does not affect the pupil or accommodation, which are functions of the parasympathetic nerves (third cranial nerve).
**Clinical Pearl / High-Yield Fact**
It's essential to note that sixth nerve palsy can be caused by a variety of factors, including aneurysms, tumors, multiple sclerosis, and trauma. A thorough history and physical examination, along with imaging studies, are necessary to determine the underlying cause of the palsy.
**Correct Answer: A. Lateral rectus muscle weakness leading to horizontal diplopia and limited abduction.**