A 50-year-old man with a history of heavy smoking presents with ipsilateral ptosis, miosis, and anhidrosis of the face, with a small palpable lymph node above the left clavicle. What is the most likely anatomical cause of the Horner's syndrome in this patient?

• A First-order neuron lesion from Wallenberg's syndrome (lateral medullary infarct)
• B Third-order (postganglionic) neuron lesion from cavernous sinus thrombosis
• C Central Horner's from a hypothalamic lesion
• D Second-order (preganglionic) neuron lesion from a Pancoast tumor at the lung apex compressing the sympathetic chain ✓

Explanation

Horner's syndrome (ptosis + miosis + anhidrosis) from a Pancoast (superior sulcus) tumor at the lung apex indicates a second-order (preganglionic) sympathetic neuron lesion. The preganglionic sympathetic fibres exit T1 and travel over the lung apex before synapsing at the superior cervical ganglion; a Pancoast tumor at this location compresses these fibres. Anhidrosis of the face confirms preganglionic involvement (facial sweat fibres travel with the external carotid artery after the superior cervical ganglion; a postganglionic lesion distal to the ganglion would spare facial sweating). The left supraclavicular lymph node suggests metastatic spread.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.