Which of the following is the main underlying mechanism responsible for Horner's syndrome?
Solution
Correct Answer: Option A
- The main underlying mechanism responsible for Horner's syndrome is the disruption of the sympathetic pathway supplying the eye and surrounding facial structures.
- This condition results from damage to the oculosympathetic nerve fibers that travel from the hypothalamus, down the brainstem and spinal cord, and then ascend along the sympathetic chain to the eye.
Key features of Horner's syndrome include:
- Miosis (constriction of the pupil) due to unopposed parasympathetic activity.
- Ptosis (drooping of the upper eyelid) caused by paralysis of the superior tarsal muscle, a smooth muscle innervated by sympathetic fibers.
- Anhidrosis (loss of sweating) on the affected side of the face.
- Enophthalmos (apparent sinking of the eyeball).
The other options do not explain Horner's syndrome:
- Damage to the oculomotor nerve (Option 2) causes a different set of signs such as ptosis with a dilated pupil (due to parasympathetic fiber loss) and eye movement abnormalities, but not the classic features of Horner's syndrome.
- Lesion in the parasympathetic fibers of the ciliary ganglion (Option 3) leads primarily to pupillary dilation and accommodation defects, not Horner's syndrome.
- Injury to the facial nerve (Option 4) results in facial muscle paralysis and other symptoms unrelated to the sympathetic pathway of the eye.
Hence, the hallmark of Horner's syndrome is a lesion affecting the sympathetic innervation.
Reference: Adams and Victor's Principles of Neurology, 11th Edition, Chapter 15: Disorders of the Motor and Autonomic Nervous System / pp. 400-405
- This condition results from damage to the oculosympathetic nerve fibers that travel from the hypothalamus, down the brainstem and spinal cord, and then ascend along the sympathetic chain to the eye.
Key features of Horner's syndrome include:
- Miosis (constriction of the pupil) due to unopposed parasympathetic activity.
- Ptosis (drooping of the upper eyelid) caused by paralysis of the superior tarsal muscle, a smooth muscle innervated by sympathetic fibers.
- Anhidrosis (loss of sweating) on the affected side of the face.
- Enophthalmos (apparent sinking of the eyeball).
The other options do not explain Horner's syndrome:
- Damage to the oculomotor nerve (Option 2) causes a different set of signs such as ptosis with a dilated pupil (due to parasympathetic fiber loss) and eye movement abnormalities, but not the classic features of Horner's syndrome.
- Lesion in the parasympathetic fibers of the ciliary ganglion (Option 3) leads primarily to pupillary dilation and accommodation defects, not Horner's syndrome.
- Injury to the facial nerve (Option 4) results in facial muscle paralysis and other symptoms unrelated to the sympathetic pathway of the eye.
Hence, the hallmark of Horner's syndrome is a lesion affecting the sympathetic innervation.
Reference: Adams and Victor's Principles of Neurology, 11th Edition, Chapter 15: Disorders of the Motor and Autonomic Nervous System / pp. 400-405
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