Harlequin syndrome is a condition describing the asymmetric flushing and sweating of the face. In this rare disorder of the autonomic nervous system, most cases are idiopathic while some occur as a consequence of thoracic surgery. Harlequin syndrome is diagnosed by the clinical appearance, physical exam, and the related testing.
Harlequin syndrome is defined by the presence of hemifacial flushing and diaphoresis . This rare condition is likely a malfunction of the sympathetic network in the upper thoracic region (with the exception of the first segment)  . Although the exact cause of this disorder is not clear and the majority of cases are idiopathic, some are iatrogenic  . For example, Harlequin syndrome is associated with the removal of neck lesions, lung resection, paravertebral thoracic block, catheterization of the jugular vein, dissection of the carotid artery, and thoracic sympathectomy  . Moreover, cases have been described to develop after resection of superior mediastinal neurinoma  and other types of compression tumors on the sympathetic chain  . Additionally, Harlequin syndrome can also result following a stroke, Horner's syndrome , and even autoimmune hyperthyroidism .
Report of a patient who underwent resection of a ganglioneuroma located on the thoracic spine developing a midline mark on the face with asymmetric flushing and warmth appearing on half of the face, neck, as well as the chest has been highlighted in the literature . The onset in such situation was shortly after surgery and discovered in the postoperative unit. Crying worsened these findings , which is consistent with the fact that Harlequin syndrome is precipitated by emotion, physical activity, and elevated temperature   . Symptoms resolved 3 hours following surgery and did not recur. While this ailment is generally benign and resolves without medical intervention a few hours after onset, some patients have been spoken about to have chronic symptoms .
In the case discussed above, there were no abnormalities in vital signs or the neurologic or cranial nerve exams . Note that a thorough neurologic exam, including the pupillary response as well as the deep tendon reflexes, should be performed .
Anyone who appears with asymmetric facial flushing and sweating following thoracic surgery warrants assessment of the clinical presentation, a physical exam with a neurologic focus, imaging, and possibly other studies. The laboratory tests are usually normal 
The workup should include imaging modalities to rule out other conditions that may cause a clinical picture similar to Harlequin syndrome. Specifically, the brain and the cervicothoracic segments of the spine should be assessed for tumors or other pathologies with computed tomography (CT) scan and magnetic resonance imaging (MRI)  .
Chronic idiopathic cases may require a sweat test for evaluation of involved body parts . Other studies include cardiovascular autonomic reflex tests, microneurography for assessment of sympathetic nerve function, and biopsy of affected skin . Very importantly, the pupillary and deep tendon reflexes should be tested as noted earlier .