Harlequin syndromeis a syndrome affecting the autonomic nervous system. The autonomic nervous system is responsible for controlling the body’s natural processes such as sweating, skin flushing, and the response of the pupils to stimuli. People with Harlequin syndrome have the absence of sweating and flushing of skin on one side of the body (unilateral), especially of the face, arms, and chest.

The symptoms associated with Harlequin syndrome may be more likely to occur when a person has been exercising, is very warm, or is in an intense emotional situation. In these situations, one side of the body sweats and flushes appropriately as a response to the situation, whereas the other side of the body does not. The asymmetrical facial sweating and flushing associated with this condition has been named the “Harlequin sign.” Harlequin syndrome is thought to be one of a spectrum of diseases that can cause Harlequin sign.

The exact cause of Harlequin syndrome is not completely understood. In some patients with this syndrome, the underlying cause seems to be a lesion or tumor that is affecting the ability of the cells of the autonomic nervous system to communicate with one side of the body. However, in many cases an exact cause of the symptoms is not found.

Diagnosis of Harlequin syndrome is based on observing symptoms consistent with the syndrome, followed by a series of tests to rule out other diseases associated with Harlequin sign. Treatment may consist of removing any lesion that may be causing the symptoms of the syndrome. If no lesion is present and the syndrome is not interfering with a person’s daily living, treatment may not be necessary.

When the nerve bundles are injured, they are not able to communicate with half of the face and body properly. Therefore, that half of the body is not able to respond to stimuli such as exercise by flushing and producing sweat. This causes the Harlequin sign that is associated with this syndrome.

In general, autoimmune diseases are thought to be caused by a combination of genetic and environmental factors. If Harlequin syndrome is caused by an autoimmune response, it is possible that the symptoms of Harlequin syndrome could occur in other members of the family with an autoimmune disease.

Some people with the Harlequin sign may have other symptoms including cluster headaches, tearing of the eyes, nasal discharge, forehead sweating, abnormal contraction of the pupils, and drooping of the upper eyelid (ptosis). There is some debate whether or not these symptoms are related to Harlequin syndrome or if they may be associated with another disease. Signs and symptoms of Harlequin syndrome may overlap with those of Ross syndrome, Aide syndrome, and Horner’s syndrome.

If Harlequin syndrome is suspected, other tests may be ordered to rule out other symptoms associated with the syndrome or other diseases with similar symptoms. These tests may include an MRI of the spine and brain to determine if there is a visible cause of the symptoms. Doctors may also want to see if there are any symptoms affecting the pupils of the eyes and the reflexes elsewhere in the body.

In cases where an individual has symptoms of Harlequin syndrome and wishes to receive treatment, injection with botulinum toxin (Botox) or a procedure called contralateral sympathectomy is possible. In contralateral sympathectomy, the nerve bundles that are responsible for causing flushing in the face are interrupted. Therefore, this procedure causes both sides of the face to no longer flush or sweat. Because the symptoms of Harlequin syndrome are not typically associated with affecting a person’s daily life, this treatment is only recommended if a person is very uncomfortable with the flushing and sweating associated with the syndrome.

It is important to determine if there is another underlying cause of the symptoms in order to receive proper treatment and accurately predict a person’s long-term outlook.