Definition
Harlequin syndrome is a rare autonomic disorder characterized by unilateral facial flushing and sweating (hyperhidrosis) accompanied by contralateral anhidrosis (absence of sweating) and pallor, typically triggered by heat, exertion, or emotional stress.
Overview
The condition results from disruption of sympathetic pathways that innervate the cutaneous vessels and sweat glands of the face, neck, and upper thorax. It may occur idiopathically or secondary to trauma, neoplasms, thoracic surgery, or vascular lesions affecting the sympathetic chain. The hallmark presentation is an abrupt, conspicuous demarcation of reddening and sweating on one side of the face and sometimes the upper trunk, while the opposite side remains pale and dry. Although primarily a cosmetic and discomfort concern, the syndrome can be associated with underlying neuropathic or compressive processes that require evaluation.
Etymology/Origin
The name “Harlequin” derives from the theatrical character Harlequin, traditionally depicted in a multicolored costume with contrasting patches. The term was adopted in medicine to describe the striking half‑and‑half facial appearance reminiscent of the character’s costume. The syndrome was first described in the medical literature in the late 20th century.
Characteristics
| Feature | Description |
|---|---|
| Cutaneous manifestations | Unilateral flushing and hyperhidrosis; opposite side shows anhidrosis and pallor. |
| Distribution | Usually involves the face, scalp, and may extend to the neck, upper chest, and arm on the affected side. |
| Triggers | Heat exposure, physical exertion, emotional stress, spicy foods, or emotional stimuli. |
| Onset | Acute onset is common; can be episodic or persistent. |
| Associated findings | May coexist with Horner’s syndrome (ptosis, miosis, anhidrosis) if the lesion involves adjacent sympathetic fibers. Neurological deficits are generally absent unless an underlying pathology is present. |
| Diagnostic evaluation | Clinical observation of asymmetric sweating; thermoregulatory sweat testing; autonomic function tests; imaging (MRI, CT) when secondary causes are suspected. |
| Management | Primarily symptomatic: avoidance of triggers, use of antiperspirants on the hyperhidrotic side, and counseling. Treatment of underlying causes (e.g., tumor resection, nerve decompression) may resolve the syndrome. |
| Prognosis | Idiopathic cases are benign and often stable; secondary cases depend on the nature and treatment of the underlying lesion. |
Related Topics
- Autonomic nervous system – The branch of the peripheral nervous system responsible for involuntary physiological functions, including thermoregulation and sweating.
- Horner’s syndrome – A neurological disorder resulting from disruption of the sympathetic trunk, characterized by ptosis, miosis, and anhidrosis.
- Complex regional pain syndrome (CRPS) – A chronic pain condition with autonomic, sensory, and motor disturbances, sometimes confused with Harlequin syndrome due to abnormal sweating patterns.
- Thoracic sympathectomy – A surgical procedure that interrupts sympathetic fibers, which can inadvertently produce Harlequin-like symptoms.
- Thermoregulatory sweating test – A diagnostic tool used to assess the distribution and symmetry of sweating, useful in evaluating Harlequin syndrome.