Source / episode info

• **Episode:**457
• **Title:**Divine Intervention Episode 457: Horner’s Syndrome (a USMLE perspective)
• **Published:**2023-05-05
• Source:Episode page

One-liner

This episode details Horner's syndrome, emphasizing its complex three-neuron sympathetic pathway and using associated symptoms (e.g., myelopathy, brainstem deficits) to localize the specific neuronal segment affected.

High-yield summary

• The Triad: Ptosis (due to paralysis of superior tarsal muscles), Miosis (constricted pupils due to loss of sympathetic dilation), and Anhidrosis (lack of sweating).
• Three-Neuron System: The pathway originates in the hypothalamus, synapses at the spinal cord (C2-T2), travels via the cervical chain/brachial plexus, and terminates at the superior cervical ganglion.
• Localization is Key: Identifying which neuron is damaged requires looking for associated signs: Brainstem deficits point to Neuron 1; Myelopathy or Brachial Plexus issues suggest Neuron 2; Ocular muscle deficits or internal carotid involvement suggests Neuron 3.
• Neuron 2 Lesions: A common cause of second-neuron damage is a Pancoast tumor (superior sulcus cancer) impinging on the sympathetic chain.
• Anatomy to Remember: The post-ganglionic fibers travel around the internal carotid artery and through the cavernous sinus, making these areas susceptible to dissection or thrombosis.

Learning objectives

• Describe the three distinct neurons involved in the sympathetic innervation to the eye and face.
• Identify the classic clinical triad associated with Horner's syndrome (ptosis, miosis, anhidrosis).
• Differentiate between first-, second-, and third-neuron lesions by recognizing specific associated neurological deficits (e.g., myelopathy vs. brainstem signs).
• Recognize common etiologies for sympathetic chain disruption, such as Pancoast tumors or carotid artery dissection.
• Understand the anatomical pathways of the post-ganglionic fibers through the internal carotid artery and cavernous sinus.

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