EUH Hunt Conference: A review of Horner syndrome

The Bottom Line: Horner syndrome results from an interruption of sympathetic innervation to the eye. The classic triad is unilateral ptosis (slight narrowing of the ocular fissure), miosis (smaller pupil on the affected side), and anhidrosis (lack of perspiration on the forehead or face). Horner syndrome is not likely to cause any functional visual disturbance but is of great importance clinically as a “red flag” warning that the oculosympathetic pathway has been interrupted and thus there may be potentially life-threatening lesions in the head, neck, and chest.

Reference: Martin TJ. Horner syndrome: a clinical review. ACS Chem Neuroscience. 2018 Feb 21;9(2):177-186. Doi:10.1021/acschemneuro.7b00405

Summary: The first, and perhaps most important, aspect of evaluating suspected Horner syndrome is a careful history. The history often reveals an obvious cause, such as trauma or neck/chest surgery, or will show that the Horner syndrome had been present for many years and therefore may not require an extensive investigation. The history may also reveal other symptoms that would help localize the lesion causing the Horner syndrome. A careful examination is obviously also critical, as other causes of anisocoria or ptosis may need to be considered rather than Horner syndrome, and concomitant signs (for example, a sixth nerve paresis) may help localize a potential lesion. After this, pharmacologic testing can be helpful to confirm diagnosis. Many clinicians will elect not to evaluate Horner syndrome if it has been present for greater than two years.

Though often benign or idiopathic, the cause of Horner syndrome can be very threatening or even lethal, so understanding how to recognize, diagnose, and appropriately evaluate Horner syndrome is important to all clinicians.