Appendix
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Neurology

Harlequin Syndrome

Harlequin syndrome is a rare dysautonomic disorder characterized by unilateral impairment of facial sudomotor and vasomotor function due to disruption of sympathetic fibers, most commonly involving the T2 to T3 segments. Etiologies include injury, compression, or iatrogenic blockade along the sympathetic pathway extending from the hypothalamus to the face. However, approximately half of the reported cases are idiopathic. Recognized risk factors include cervical or upper thoracic surgery, regiona

v1 · Reviewed Nov 8, 2026 by Automated Clinical Reviewer (Strict Verbatim v1)
  • Further evaluation is warranted in patients with new-onset idiopathic symptoms, persistent or progressive findings, associated pain, Horner syndrome, neurologic deficits, or concern for structural or vascular pathology.
  • Diverse underlying pathologies may produce similar Harlequin facies and must be excluded before establishing a diagnosis of primary Harlequin syndrome.
  • The diagnosis of Harlequin syndrome is primarily clinical, based on characteristic unilateral facial flushing in the appropriate context.
  • Chest radiography, computed tomography, or magnetic resonance imaging of the lung apex, carotid arteries, spinal cord, and brain may be necessary to exclude secondary causes before classifying a case as idiopathic.
  • Quantitative sudomotor axon reflex testing (QSART) and thermoregulatory sweat testing (TST) provide objective assessment of sympathetic sudomotor function when indicated.
  • Reassurance and patient education constitute the primary management approach.
  • Idiopathic Harlequin syndrome is benign and self-limiting, resolving once the triggering stimulus subsides.
  • Avoidance of known triggers may reduce the occurrence of Harlequin facies.
  • Head-up positioning and reduction or cessation of local anesthetic infusion may facilitate recovery.
  • Management of the underlying pathology is essential when secondary causes are identified.
  • For persistent and socially distressing symptoms, interventional therapies such as sympathetic block, botulinum toxin injection, or sympathectomy have been reported; however, the evidence supporting these measures is limited to case reports and small series, and they should therefore be reserved for selected patients.
  • No direct long-term complications are associated with Harlequin syndrome itself.
  • However, extensive underlying lesions can produce broader autonomic dysfunction and necessitate further evaluation.
  • Recurrent episodes can occur with repeated exposure to triggers.
  • Prognosis is favorable, particularly in idiopathic or transient cases.
  • review
    Harlequin Syndrome. StatPearls [Internet] — Hem R. Joshi, Jagkirat Singh, Senthil Packiasabapathy — StatPearls Publishing, 2026

Decision support only. Verify against local protocols and current labeling. Source: www.ncbi.nlm.nih.gov