Cranial nerve commonly involved in Guillain Barre syndrome is: March 2009
**Core Concept**
Guillain-Barre Syndrome (GBS) is an autoimmune disorder where the body's immune system mistakenly attacks the peripheral nerves, leading to demyelination and nerve dysfunction. The cranial nerves, being part of the peripheral nervous system, can also be affected in GBS.
**Why the Correct Answer is Right**
In GBS, the cranial nerves are commonly involved, particularly the cranial nerves responsible for controlling eye movements and facial functions. The most commonly affected cranial nerves are CN III (oculomotor), CN IV (trochlear), CN VI (abducens), and CN VII (facial). The involvement of these cranial nerves can lead to symptoms such as diplopia (double vision), ptosis (drooping eyelid), and facial weakness. The exact mechanism of cranial nerve involvement in GBS is not fully understood, but it is thought to be related to the autoimmune response against the peripheral nerves.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not a specific cranial nerve commonly involved in GBS.
* **Option B:** This option is incorrect because it is not a cranial nerve, but rather a spinal nerve that can be affected in GBS.
* **Option C:** This option is incorrect because it is not a commonly affected cranial nerve in GBS.
**Clinical Pearl / High-Yield Fact**
The Miller Fisher variant of GBS is a rare subtype that specifically affects the cranial nerves, leading to ophthalmoplegia (weakness of the eye muscles), ataxia, and areflexia. This variant is often associated with a worse prognosis than the classic GBS.
**Correct Answer:** C.