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Horner's syndrome in a young man, showing a constricted right pupil (left of image) and drooping upper eyelid (ptosis). Horner's syndrome describes a group of symptoms that are due to a disorder of sympathetic nerves in the neck. An additional symptom is the absence of sweating over the affected side of the face. The syndrome may indicate a chest malignancy (cancer) but is often idiopathic (without obvious cause), as in this case.
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