Which trio of signs constitutes Horner syndrome?

• A. Ptosis, miosis, and anhidrosis
• B. Ptosis, mydriasis, and facial flushing
• C. Exophthalmos, diplopia, and lid retraction
• D. Nystagmus, tremor, and ataxia

Answer: (A)

Horner syndrome comes from a disruption of the sympathetic pathways to the eye and face. When these sympathetic nerves are impaired, the eye loses the sympathetic drive that normally dilates the pupil and elevates the upper lid. The result is a small pupil (miosis) and drooping of the eyelid (ptosis). Sweat glands on the affected side may also lose sympathetic input, causing reduced or absent sweating (anhidrosis). Taken together, ptosis, miosis, and anhidrosis form the classic triad that identifies Horner syndrome.

The other sets of signs don’t fit Horner because they reflect different conditions: a dilated pupil would point away from Horner and toward issues with the oculomotor nerve; exophthalmos with diplopia and lid retraction suggests Graves disease or other orbital pathology; and nystagmus, tremor, and ataxia point to cerebellar or vestibular problems.