Horner's syndrome in the emergency department

We present a case of a 47-year-old female who was followed for 7 months with complaints of musculoskeletal pain involving the shoulder and scapula until she presented to the emergency department with Horner's syndrome and was diagnosed as having a superior pulmonary sulcus tumor. A review of the literature shows that although such tumors are a frequent cause of Horner's syndrome there are numerous other benign as well as malignant causes of Horner's syndrome. The differential diagnosis can be significantly narrowed by a knowledge of the anatomy and a careful physical examination. We present the anatomy, pathophysiology, differential diagnosis, and evaluation of patients who present to the emergency department with Horner's syndrome.