Topic: Horner's Syndrome
Subject: Medicine
A 70-year-old man presented with ptosis, myosis and anhydrosis on the left side. Which one of the following is the most likely cause of this condition?

Horner's syndrome results when the cervical sympathetic pathway running from the hypothalamus to the eye is disrupted. The syndrome may be central, preganglionic, or postganglionic in origin; it may be primary or secondary to another disorder.
An apical bronchogenic carcinoma (eg Pancoast tumor) is the most common cause of Horner syndrome. Central lesions include brain stem ischemia, syringomyelia, and brain tumor; peripheral lesions include Pancoast tumor, thyrocervical venous dilatation, cervical adenopathy, neck and skull injuries, aortic or carotid dissection, and thoracic aortic aneurysm. A congenital form exists. Symptoms include ptosis, miosis, anhidrosis, and hyperemia of the affected side. In the congenital form, the iris does not become pigmented and remains blue-gray. Liquid cocaine 10% can be applied to the affected eye; poor pupillary dilation after 30 min indicates Horner's syndrome. If results are positive, 1% hydroxyamphetamine solution or 5% n-methyl hydroxyamphetamine can be applied to the eye 48 h later to determine whether the lesion is preganglionic (if the pupil dilates) or postganglionic (if the pupil does not dilate).