Harlequin syndrome

Overview

Harlequin syndrome is a rare autonomic nervous system disorder characterized by asymmetric facial flushing and sweating, typically triggered by heat, exercise, or emotional stimuli. The condition results from damage or dysfunction in the sympathetic nerves that control sweating (sudomotor) and blood vessel dilation (vasomotor) on one side of the face. First described in the 1980s, Harlequin syndrome is usually benign but can sometimes be associated with underlying neurological or structural conditions.

Causes

Harlequin syndrome is caused by disruption of the sympathetic nervous pathways, particularly those involving the T2–T3 thoracic nerve roots. This disruption can occur due to:

• Idiopathic origin (no identifiable cause, most common)

• Trauma or surgical injury to the upper chest or neck

• Brainstem or spinal cord lesions

• Tumors (e.g., Pancoast tumors, neuroblastoma)

• Multiple sclerosis or other demyelinating diseases

• Vascular abnormalities, such as carotid artery dissection

Symptoms

The hallmark symptom of Harlequin syndrome is unilateral facial flushing and sweating. Common features include:

• Hemifacial flushing: One side of the face turns red while the other remains pale

• Hemihidrosis: Sweating only on one side of the face, or complete absence of sweating on the other

• Triggering events: Symptoms are most noticeable during exercise, heat exposure, or emotional stress

• No pain or systemic illness: Most cases are isolated and not accompanied by other symptoms

In some cases, Harlequin syndrome may be associated with other neurological conditions such as Horner’s syndrome, which includes ptosis (drooping eyelid), miosis (constricted pupil), and anhidrosis (lack of sweating) on the affected side.

Diagnosis

Diagnosis of Harlequin syndrome is primarily clinical and based on characteristic symptoms. Key diagnostic steps include:

• Clinical history and observation: A detailed review of symptoms, especially during physical exertion

• Neurological examination: To assess for any associated syndromes or neurological deficits

• Imaging studies: MRI or CT scans of the brain, cervical spine, and chest to detect underlying causes such as tumors or structural lesions

• Autonomic function testing: May be done to evaluate sympathetic nervous system integrity

Treatment

Treatment for Harlequin syndrome depends on whether an underlying cause is identified:

• Idiopathic cases: No treatment may be necessary if the condition is benign and non-progressive

• Underlying condition: Management focuses on treating the root cause (e.g., tumor removal, vascular repair)

• Cosmetic or functional concern: Options like contralateral sympathectomy (rarely performed) may restore facial symmetry in extreme cases

• Patient education and reassurance: Explaining the benign nature of the syndrome often helps manage concerns

Prognosis

The prognosis of Harlequin syndrome is generally excellent, particularly in idiopathic cases. The condition is non-life-threatening and does not usually progress. While the cosmetic aspect may be distressing for some individuals, it typically does not impact daily functioning or overall health. Prognosis may vary if an associated underlying condition is discovered, in which case outcome depends on the nature and treatment of that condition.