Background: Horner's syndrome is characterized by the classic triad of eyelid ptosis, miosis and facial anhidrosis and is caused by an interruption of the oculosympathetic nerve pathway somewhere between its origin in the hypothalamus and the eye.
Material and methods: This review is based on own experiences and a discretionary selection of articles found through non-systematic searches in PubMed. Cases from own practice serve as examples.
Results: Based on localization of the nerve pathway interruption, a Horner's syndrome is often classified as central, pre- or postganglionic. For the central type the syndrome is associated with other symptoms and signs from the central nervous system. The preganglionic type is most often caused by a tumor or trauma. The postganglionic type is often associated with pain/headache; most frequently it is seen as a consequence of carotid artery dissection or during cluster headache. Anhidrosis is rarely prominent, and in the postganglionic subtype it is virtually absent. Pharmacological tests can be used in diagnostics. Apraclonidine seems to be a good alternative to cocaine to confirm Horner's syndrome. MRI is generally recommended in the evaluation, if necessary with special sequences.
Interpretation: The path of the long oculosympathetic fibers is complex and not fully understood. Topographic diagnostics may be challenging, but in most cases a specific cause is identified.