What is Systemic Capillary Leak Syndrome (SCLS)? Symptoms, Diagnosis, and Treatment

Systemic Capillary Leak Syndrome

Systemic capillary leak syndrome (SCLS) is known in medical literature as a condition characterized by a temporary but potentially fatal impairment in the function of capillaries, the body's smallest blood vessels. Normally, blood fluid, known as plasma, is tightly contained within the vessel wall; in this syndrome, the vessel wall becomes permeable, allowing plasma and proteins to leak into surrounding tissues, muscles, or cavities.

What is Systemic Capillary Leak Syndrome?

Systemic capillary leak syndrome (SCLS) is a very rare and potentially serious vascular disease. At its core lies a sudden increase in the permeability of capillaries. Normally, the vessel wall keeps the liquid part of the blood, i.e., plasma, inside the vessel. In this syndrome, the balance on the inner surface of the vessels is disrupted, and plasma leaks out of the vessels in an uncontrolled manner. This event creates a type of internal fluid loss in the body.

During an SCLS attack, blood pressure drops rapidly, blood concentration (hematocrit) increases, and widespread edema occurs in the tissues. This clinical picture usually begins with prodromal symptoms such as weakness, dizziness, and nausea; in the following hours, it can progress to a state of shock. If left untreated, it can pose a life-threatening risk. Systemic capillary leak syndrome usually starts suddenly and develops in an attack-like manner. In some individuals, these attacks may recur. Although rare, in some cases, viral infections, an overreaction of the immune system, or certain medications can trigger this process. While the exact cause is not fully known, research suggests that microscopic damage caused by the immune system to the vessels leads to this leakage.

What Are the Symptoms of Systemic Capillary Leak Syndrome?

The symptoms of systemic capillary leak syndrome often start insidiously and may not be very obvious in the early stages of the disease. As the condition progresses, symptoms rapidly intensify and become a state requiring emergency intervention. Usually, in the pre-attack period, the person feels weak, tired, and as if they have the flu. Some patients describe muscle aches, nausea, dizziness, or a mild fever during this phase. These symptoms may last for a few hours or a day. Sudden fluid loss, muscle aches, and low blood pressure can be harbingers of an SCLS crisis.

The real danger arises when the leakage phase begins. In this phase, a large amount of fluid passes from inside the vessels to the surrounding tissues. For this reason, the body experiences severe fluid loss. As a result, blood pressure drops suddenly (hypotension), the patient may faint, or a state of shock may develop. At the same time, while the fluid inside the vessel decreases, the blood thickens because the number of cells remains constant; consequently, the value called hematocrit rises. The leakage of important proteins such as albumin out of the vessels manifests itself both in laboratory values and in the formation of edema. Sudden and widespread swelling may be seen in the arms, legs, or abdominal region. In some patients, systemic capillary leak syndrome may start with itching and progress to serious circulatory problems.

Symptoms are felt not only physically but also at the organ level. If blood flow to the heart decreases, arrhythmias may occur; if blood flow to the kidneys decreases, a drop in urine output may occur; and if less blood goes to the brain, confusion or fainting may occur. If fluid returns to the lungs, shortness of breath and severe respiratory distress may develop during the recovery phase.

How Does Systemic Capillary Leak Syndrome Occur?

Although the exact causes of systemic capillary leak syndrome are not known, it is thought to be caused by excessive responses of the immune system. In some cases, factors such as infections or stress are cited among the causes of systemic capillary leak syndrome. Systemic capillary leak syndrome is the result of a highly specific and rare disorder related to the body's vascular system. In this disease, the permeability of capillaries, which should normally only allow necessary substances such as nutrients and oxygen to pass, suddenly increases. This increase reaches such a magnitude that a large portion of the fluid inside the vessel leaks into the surrounding tissues along with plasma proteins. This fluid loss does not occur in the form of visible external bleeding; the body essentially experiences an internal fluid drainage. This causes insufficient fluid and oxygen to reach the organs.

Although the exact cause of this process is not scientifically known, an abnormal response of the immune system plays a triggering role in many cases. Especially some infections are frequently seen before an attack. Research has shown that endothelial cells in the vessel wall respond excessively to certain immune-stimulating molecules (e.g., interleukin-6, TNF-alpha). As a result of these reactions, the intravascular barrier is disrupted and fluid leakage begins. In some patients, the presence of certain proteins in the blood (monoclonal gammopathy) may also contribute to this process. Attacks that develop as a result of all these mechanisms can progress rapidly enough to create a life-threatening danger in as little as a few hours.

How Is Systemic Capillary Leak Syndrome Diagnosed?

The diagnosis of systemic capillary leak syndrome is mostly made by evaluating clinical observation and laboratory data together because the disease is very rare and can show similar symptoms to many other conditions. For this reason, the diagnostic process often requires the careful exclusion of other possibilities. To make a diagnosis, the patient's clinical history is first carefully examined. It is questioned whether they have had similar attacks before, how these attacks progressed, and how long it took for them to recover. In addition, accompanying diseases are taken into account. In some patients, a condition called monoclonal gammopathy is detected. This is characterized by an abnormal increase in a certain type of antibody in the blood and is thought to have a strong relationship with SCLS.

Blood tests, urine tests, and, if necessary, imaging methods are used to support the diagnosis. These tests play a more supportive role. Especially in the first attack, making a diagnosis is not easy. In many cases, the diagnosis becomes clear after a few attacks have occurred and other causes have been excluded. Therefore, it is of great importance that patients suspected of having SCLS are followed by an experienced internal medicine or intensive care specialist. Early diagnosis, appropriate fluid therapy, and preventive approaches can significantly increase quality of life and survival chances.

How Is Systemic Capillary Leak Syndrome Treated?

The treatment of systemic capillary leak syndrome is a process as complex and demanding as the course of the disease itself. The treatment approach is divided into two main headings: emergency intervention during an attack and long-term treatment to prevent the recurrence of attacks. The first thing to do when an attack begins is to quickly admit the patient to an intensive care unit to stabilize their vital signs. This is because, in this phase, the patient has lost a large portion of the fluid inside the vessels, and this situation can lead to severe hypotension, shock, and multiple organ failure.

During the treatment process, the treatment of systemic capillary leak syndrome is aimed at controlling symptoms and preventing possible crises. The most critical intervention in the leakage phase is the controlled administration of intravenous fluids. If too much fluid is given, these fluids can lead to serious respiratory distress as they return to the lungs during the recovery phase. For this reason, fluid support should be adjusted meticulously according to the patient's needs. At the same time, immune-regulating drugs such as corticosteroids and immunoglobulin (IVIG) can be used to reduce vascular permeability and control the excessive response of the immune system.

In long-term treatment, the goal is to prevent new attacks. For this, high-dose immunoglobulin (IVIG) therapy stands out. Clinical studies and case series show that monthly IVIG therapy both reduces the frequency of attacks and decreases the severity of the disease. In some patients, drugs that reduce vascular permeability, such as theophylline or terbutaline, can also be used. These agents are more supportive in nature and may not provide sufficient effect on their own.

Success in the treatment of systemic capillary leak syndrome is possible through the combination of early diagnosis, conscious fluid management during the attack period, and regular preventive treatment. Treatment should be planned individually and supported by long-term follow-up under the guidance of experienced specialists, because every neglected attack in this syndrome carries the risk of permanent organ damage or loss of life.

Frequently Asked Questions

Systemic capillary leak syndrome is not a contagious disease; that is, it is not a type of infection that passes from person to person like the flu, a cold, or COVID-19. The emergence of this syndrome is responsible for certain disorders of the body's immune system and excessive permeability in the vascular structure. Although viral infections can be among the conditions that trigger attacks in some cases, these viruses do not directly transmit systemic capillary leak syndrome; they only initiate the attack by creating a sudden and abnormal response in the immune system. Therefore, systemic capillary leak syndrome is a rare and individual vascular disease seen only in certain people and individuals with certain immune tendencies. Systemic capillary leak syndrome (SCLS) is an extremely rare disease worldwide. The number of cases reported to date is less than 500, and these cases are generally cases that have entered medical literature and have been documented with scientific publications. Due to its rarity, we do not have large-scale epidemiological data about the disease. The disease can affect both women and men, but it is generally identified more frequently in the middle-age group (especially between 30-50 years old). Due to its rarity, it is usually confused with other diseases in the first attack, and the diagnosis is made after recurrent attacks. Although this suggests that the actual number of patients may be higher than reported, in general, systemic capillary leak syndrome is considered an ultra-rare disease worldwide. Systemic capillary leak syndrome is not clinically divided into distinct subtypes; some classifications can be made according to its course and associated findings. The most widely accepted distinction is the primary and secondary forms of the disease:

Primary Systemic Capillary Leak Syndrome (Idiopathic SCLS): This is the form whose cause is not fully known and is usually not associated with another underlying disease. In most of these patients, an antibody disorder called monoclonal gammopathy is detected in blood tests. This condition is not always an active disease.

Secondary Systemic Capillary Leak Syndrome: In this form, systemic capillary leak syndrome occurs as a result of another disease. Especially severe infections (e.g., sepsis), certain types of cancer, autoimmune diseases, or hematological disorders can lead to a clinical picture similar to systemic capillary leak syndrome. Since the secondary form often develops as part of another disease, the treatment approach may also differ.

In addition to these, some experts also make practical classifications according to the course of the disease, such as those who have a single attack, those who have recurrent attacks, and severe cases requiring intensive care support. These distinctions are used more to guide treatment strategies. Basically, the disease is a condition that is evaluated within a single clinical framework and progresses with different severity and frequency.

Although systemic capillary leak syndrome is rare, it is a life-threatening disease that requires expertise. Early recognition of attacks, accurate diagnosis, and a conscious treatment process are of critical importance in terms of quality of life.

At Hisar Hospital Intercontinental, the diagnosis, treatment, and long-term follow-up of systemic capillary leak syndrome are handled with a multidisciplinary approach by our expert staff experienced in internal medicine, immunology, and intensive care.

If you have symptoms or have experienced similar attacks before, you can apply to our expert Cardiology physicians for early evaluation.

Contact us for detailed information and appointments.