Capillary leak syndrome


Capillary leak syndrome is a medical condition characterized by the leakage of plasma, the liquid part of blood, from small blood vessels known as capillaries into the surrounding muscles, tissues, organs, and body cavities. The frequency of capillary leak syndrome episodes can vary, occurring multiple times within a year or possibly only once. If not treated promptly, capillary leak syndrome can lead to a rapid decrease in blood pressure, organ failure, and can be life-threatening.

There are two main categories of capillary leak syndrome:

  • Systemic capillary leak syndrome, also known as primary capillary leak syndrome or Clarkson’s disease, typically manifests through recurrent episodes in individuals who are otherwise healthy.
  • Secondary capillary leak syndrome refers to a single episode initiated by another illness, condition, or medication.

While there is no definitive cure for capillary leak syndrome, immediate medical intervention is essential to manage symptoms. Ongoing medication or infusion therapies may assist in preventing future episodes of systemic capillary leak syndrome.

The progression of a capillary leak syndrome episode can be broken down into three distinct phases:

  • Initial or prodromal phase: This preliminary phase typically unfolds one to two days prior to the onset of an episode. During this time, individuals may begin to notice early symptoms such as a general sense of fatigue, an unusual feeling of thirst, and a rapid increase in weight.
  • Leak or resuscitation phase: This phase coincides with the actual episode. It is characterized by the escape of fluids and albumin—a type of protein found in blood plasma—from the capillaries into the surrounding tissues. This leakage impedes the normal flow of oxygen-rich blood to tissues, leading to a drop in blood pressure and a concentration of red blood cells. The outcome is hypovolemia, a condition marked by a reduced volume of circulating blood in the body.
  • Recovery or post-leak phase: Following the episode, this phase marks the period of recuperation. During this time, the capillaries begin to reabsorb the previously leaked fluids and albumin from the tissues, potentially leading to an excess of fluids in the body. This can manifest as excessive urine production (polyuria) and the accumulation of fluid in the lungs (pulmonary edema).


The signs and symptoms of prodromal phase may include the following:

  • Abdominal pain
  • Fatigue or weakness.
  • Headache.
  • Irritability.
  • Muscle pain (myalgia).
  • Nausea.
  • Sudden body weight increase.
  • Thirst.
  • Viral or upper respiratory tract infection.

The signs and symptoms for leak or resuscitation phase may vary from person to person. The common indicators include the following:

  • Diarrhea.
  • Hypercoagulability, or thickened blood, brought on by an increased count of red blood cells (hematocrit) or white blood cells (leukocytosis).
  • Low blood pressure or hypotension.
  • Swelling of the body, legs, and arms (peripheral edema).


The following may cause capillary leak syndrome:

  • Systemic capillary leak syndrome: It is unclear what causes systemic capillary leak syndrome. Researchers believe that the disorder may be brought on by the immune system’s reaction to an infection or sickness.
  • Secondary capillary leak syndrome: Secondary capillary leak syndrome is most frequently caused by sepsis, a potentially fatal infection-related consequence. The following diseases can also result in capillary leak syndrome:
    • Autoimmune diseases: An immune system attack on your body’s healthy cells.
    • Differentiation syndrome: A side effect of medication used to treat acute myeloid leukemia or acute promyelocytic leukemia.
    • Engraftment syndrome: A potential side effect following a bone marrow transplant.
    • Hemophagocytic lymphohistiocytosis: A potentially fatal condition brought on by an excessive immunological reaction.
    • Ovarian hyperstimulation syndrome: A side effect of fertility medicine.
    • Ricin poisoning.
    • Snakebites.
    • Viral hemorrhagic fevers: A collection of virally-induced infectious illnesses.

Secondary capillary leak syndrome can also be brought on by some pharmaceuticals, such as the chemotherapy agents tagraxofusp (Elzonris) and gemcitabine (Gemzar).

Risk factors

The following may increase the risk for capillary leak syndrome:

  • Systemic capillary leak syndrome: There are less than 500 cases of systemic capillary leak syndrome worldwide, making it an uncommon condition. Rarely occurring in children, systemic capillary leak syndrome primarily affects those in their middle years. The incidence may be greater since systemic capillary leak syndrome patients frequently receive the incorrect diagnosis.
  • Secondary capillary leak syndrome: People of any age can develop secondary capillary leak syndrome. Capillary leak syndrome may result from specific illnesses, infections, or drugs.