To investigate the natural course of iatrogenic Horner's syndrome induced by procedures in the neck and upper thoracic areas.

Four patients who developed ptosis after undergoing procedures near the neck and upper thoracic areas were diagnosed with iatrogenic Horner's syndrome. We evaluated the clinical courses of the patients retrospectively. We also performed a systematic Medline search through Pubmed to find patients with iatrogenic Horner's syndrome. We summarized onset times and natural courses of reported cases.

In two cases, ptosis improved completely within 2 and 4 months. In the other two cases, ptosis persisted through the last follow-up. As a result of our Medline search, we identified 51 cases in 47 journals. In 31 patients (62%), symptoms improved from 17 minutes to 3 months after surgery. However, in 20 patients (38%), symptoms persisted for up to 20 months.

Although the mechanism underlying iatrogenic Horner's syndrome induced by procedures in the neck and upper thoracic area is not clearly understood, the syndrome may occur when the sympathetic nerve pathway is damaged directly or indirectly. Surgical correction should be postponed because this rare complication may resolve spontaneously within 4 months. The surgeon should explain the possibility of Horner's syndrome to patients after neck and upper thoracic surgery.