BACKGROUND AND IMPORTANCE: Harlequin syndrome is a rare neurological condition 
involving various degrees of unilateral hyperhidrosis and erythema of the head 
and neck. We present a clinical presentation and description of curative therapy 
in a patient with a sudden onset of Harlequin syndrome following a thoracotomy.
CLINICAL PRESENTATION: A 42-year-old female with a history of mastectomy for 
right-sided breast cancer subsequently had a left partial pneumonectomy for a 
metastasis. Postoperatively, she had onset of contralateral neck and facial 
flushing and sweating. Flushing was triggered by emotion and exercise, but also 
occurred spontaneously at random intervals. Magnetic resonance imaging of the 
brain, cervical spine, and thoracic spine were negative for pathology. Because 
of the patient's surgical history and negative workup, she was given a diagnosis 
of Harlequin syndrome. Surgical intervention consisted of a partial right T3 
costotransversectomy with T2 sympathectomy. Postoperatively, the patient's 
symptoms of Harlequin syndrome resolved. The procedure was complicated by T1 
radicular pain, which responded well to Gabapentin.
CONCLUSION: The diagnosis of Harlequin syndrome is relatively new, and the 
majority of the scientific literature is concerned with descriptive case 
presentations. We present a surgical technique for the treatment of Harlequin 
syndrome.