Prolonged Horner's Syndrome After Interscalene Nerve Block: A Case Report and Summary of the Literature.

Horner's syndrome is a well-known complication of interscalene nerve blocks and is caused by a disruption along the oculosympathetic pathway that results in the classic triad of ipsilateral miosis, ptosis, and anhidrosis, although the presence of anhidrosis may vary based on anatomy and location of injury. While symptoms typically subside promptly with the resolution of anesthesia, long-lasting Horner's syndrome is a documented side effect. The authors report the case of a 43-year-old woman with prolonged Horner's syndrome following an interscalene nerve block and shoulder surgery. The authors also review similar cases of persistent Horner's syndrome following interscalene brachial plexus blocks, which has only rarely been reported in the literature.