Harlequin Syndrome is a rare, temporary disorder of the autonomic nervous system (ANS) that manifests as striking, asymmetrical changes in skin appearance. It is characterized by the sudden onset of flushing and sweating on only one side of the body, typically on the face, neck, and upper chest. This dysautonomic condition stems from a dysfunction in the system controlling involuntary bodily functions, including blood vessel dilation and perspiration. The primary form is generally benign.
The Distinctive Visual Presentation
The most recognizable feature of Harlequin Syndrome is the stark difference in coloration and moisture between the two sides of the body, often called the Harlequin sign. When an episode is triggered, one half of the face and upper body appears flushed and red, while the opposite half remains pale or its normal color. This dramatic shift is clearly separated by the body’s midline, creating a visual effect similar to the costume of the Italian theater character Harlequin.
The reddened side of the skin is often noticeably warmer to the touch and experiences normal or even excessive sweating, a phenomenon called hyperhidrosis. Conversely, the pale side remains dry and cooler, lacking both the normal red flush and any perspiration, a condition known as anhidrosis. This asymmetry is most prominent following events that naturally cause flushing and sweating, such as intense physical exertion, exposure to heat, or strong emotional responses.
Episodes can last anywhere from a few seconds to several hours before the skin color and temperature normalize completely. The condition’s effects are typically confined to the face, neck, and upper chest, but can sometimes extend to the arms.
The Role of the Autonomic Nervous System
Harlequin Syndrome involves the sympathetic branch of the autonomic nervous system (ANS). This system regulates automatic body processes like heart rate, breathing, and blood vessel size. The sympathetic nervous system normally signals blood vessels to constrict and sweat glands to activate in response to stimuli like heat or exercise.
The syndrome results from damage to the sympathetic nerve fibers supplying one side of the body. This damage often occurs along the nerve pathway in the neck or upper chest, potentially affecting the T2 and T3 ganglia. When these nerves are blocked or injured, the signals for blood vessel constriction and sweating cannot reach the affected side.
On the side with the nerve damage, the blood vessels remain dilated, leading to flushing and heat. The sweat glands fail to activate, causing the dry, pale appearance. The unaffected side attempts to compensate for the lack of heat loss, often resulting in exaggerated flushing and sweating.
Confirming the Diagnosis and Prognosis
Diagnosis is primarily based on clinical observation of the characteristic asymmetrical flushing and sweating following a trigger. Physicians may use specialized tests to confirm sympathetic dysfunction and rule out other conditions. For instance, the thermoregulatory sweat test can objectively map the areas of anhidrosis by measuring sweat production.
Pharmacological testing or a tilt-table test may assess the integrity of the ANS. The condition is classified as either primary (idiopathic), meaning no underlying cause is found, or secondary, which is linked to issues like injury, tumor, or surgical complication. Imaging, such as an MRI of the cervical and thoracic spine, may be performed to check for structural lesions compressing the sympathetic nerves.
For patients with primary Harlequin Syndrome, the prognosis is excellent, as the condition is benign and self-limiting, often requiring no treatment. Management usually involves patient reassurance and education about the harmless nature of the episodes. If the case is secondary, the long-term outlook depends on the successful treatment of the underlying cause, which may lead to the resolution of symptoms.