biology

Harlequin syndrome

Harlequin syndrome is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Harlequin syndrome rather than just read about it. In short: Harlequin syndrome, also known as "harlequin sign", is a condition characterized by asymmetric sweating and flushing on the upper thoracic region of the chest, neck and face. Harlequin syndrome is considered an injury to the autonomic nervous system (ANS).

Key takeaways

Harlequin syndrome belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Harlequin syndrome to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Harlequin syndrome from memory before moving on to harder problems.

Reference excerpt

Harlequin syndrome, also known as "harlequin sign", is a condition characterized by asymmetric sweating and flushing on the upper thoracic region of the chest, neck and face. Harlequin syndrome is considered an injury to the autonomic nervous system (ANS). The ANS controls some of the body's natural processes such as sweating, skin flushing and pupil response to stimuli. Individuals with this syndrome have an absence of sweat skin flushing unilaterally, usually on one side of the face, arms and chest. It is an autonomic disorder that may occur at any age. Symptoms associated with Harlequin syndrome are more likely to appear under the following conditions: vigorous exercise, warm environments and intense emotional situations. Since one side of the body sweats and flushes appropriately to the condition, the other side of the body will have an absence of such symptoms. Harlequin syndrome can alternatively be the outcome of a one-sided endoscopic thoracic sympathectomy (ETS) or endoscopic sympathetic blockade (ESB) surgery. It can also be observed as a complication of veno-arterial extracorporeal membrane oxygenation (ECMO). This involves differential hypoxemia (low oxygen levels in the blood) of the upper body in comparison to the lower body.

Signs and symptoms The "Harlequin sign" is unilateral flushing and sweating of the face, neck, and upper chest usually after exposure to heat or strenuous exertion. Horner syndrome, another problem associated with the sympathetic nervous system, is often seen in conjunction with harlequin syndrome. Since Harlequin syndrome is associated with a dysfunction in the autonomic nervous system, main symptoms of this dysfunction are in the following: Absence of sweat(anhidrosis) and flushing on one side of the face, neck, or upper thoracic area. In addition, other symptoms include cluster headaches, tearing of the eyes, nasal discharge, abnormal contraction of the pupils, weakness in neck muscles, and drooping of one side of the upper eyelid.

Causes One possible cause of Harlequin syndrome is a lesion to the preganglionic or postganglionic cervical sympathetic fibers and parasympathetic neurons of the ciliary ganglion. It is also believed that torsion (twisting) of the thoracic spine can cause blockage of the anterior radicular artery leading to Harlequin syndrome. The sympathetic deficit on the denervated side causes anhidrosis (lack of sweating). Patients with Horner's Syndrome may also experience this. The parasympathetic deficit on the denervated side causes the flushing of the opposite side to appear more pronounced. It is unclear whether or not the response of the undamaged side was normal or excessive, but it is believed that it could be a result of the body attempting to compensate for the damaged side and maintain homeostasis.

Mechanism Although the exact mechanism for Harlequin syndrome is still unclear, understanding what is affected with this syndrome is important. The majority of cases are thought to occur when nerve bundles in the head and neck are injured. Such bundles are able to send an action potential from the autonomic nervous system to the rest of the body. However, action potentials in this system are not being received by the second or third thoracic vertebrae which innervates the face, neck, and upper chest.

Damage or lesions near T2 or T3 could be between the stellate ganglion and superior cervical ganglion. This is where we would observe absence of sweat and skin flushing on one side of the face, neck, and upper chest.

Diagnosis Diagnosis of Harlequin syndrome is made when the individual has consistent signs and symptoms of the condition, therefore, it is made by clinical observation. In addition, a neurologist or primary care physician may require an MRI test to rule out similar disorders such as Horner's syndrome, Adie's syndrome, and Ross' syndrome. In an MRI, a radiologist may observe areas near brain or spinal cord for lesions, or any damage to the nerve endings. It is also important that the clinician rules out traumatic causes by performing autonomic function tests. Such tests includes the following: tilt table test, orthostatic blood pressure measurement, head-up test, valsalva maneuver, thermoregulatory sweat test, tendon reflex test, and electrocardiography (ECG). CT scan of the heart and lungs may also be performed to rule out a structural underlying lesion. The medical history of the individual should be carefully noted.

Treatment and prognosis Harlequin syndrome is not debilitating, so treatment is not normally necessary. In cases where the individual may feel socially embarrassed, contralateral sympathectomy may be considered, although compensatory flushing and sweating of other parts of the body may occur. In contralateral sympathectomy, the nerve bundles that cause the flushing in the face are interrupted. This procedure causes both sides of the face to no longer flush or sweat. Since symptoms of Harlequin syndrome do not typically impair 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.

Epidemiology Harlequin syndrome affects fewer than 1000 people in the United States of America. The frequency is reported as less than 1 in 1,000,000.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Harlequin syndrome

Start with the simplest possible case. Write down what Harlequin syndrome claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Harlequin syndrome before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Harlequin syndrome ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Harlequin syndrome

In research: Harlequin syndrome appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Harlequin syndrome in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Harlequin syndrome is common in secondary-school and first-year university syllabi. It links to neighbouring topics Rare diseases, Syndromes affecting the nervous system, so understanding it makes those chapters shorter.
In everyday life: Look for Harlequin syndrome outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Harlequin syndrome in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Harlequin syndrome means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Harlequin syndrome out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Harlequin syndrome in simple terms?

Why does Harlequin syndrome matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Harlequin syndrome?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Harlequin syndrome.