Systemic capillary leak syndrome (SCLS), also known as Clarkson's disease or capillary leak syndrome, is a rare medical condition characterized by recurrent episodes of severe and potentially life-threatening swelling (edema), sudden drops in blood pressure, and low levels of blood proteins.

The exact cause of SCLS is not fully understood, but it is thought to be related to dysfunction in the lining of blood vessels, which leads to an abnormal increase in the permeability of small blood vessels (capillaries). This increased permeability causes fluid and proteins to leak out of the blood vessels and into surrounding tissues, resulting in the characteristic symptoms of SCLS.

Symptoms of SCLS typically include sudden and severe swelling in the limbs, abdomen, and face, as well as fatigue, nausea, vomiting, and low blood pressure. The onset of symptoms is often sudden, with episodes lasting from several hours to several days.

There is no cure for SCLS, and treatment is focused on managing symptoms and preventing complications. Treatment may involve intravenous fluids to maintain blood pressure, medications to reduce swelling, and close monitoring in a hospital setting during acute episodes. In addition, some people with SCLS may benefit from prophylactic treatments such as intravenous immunoglobulin (IVIG) or theophylline to prevent future episodes. However, the effectiveness of these treatments in SCLS is still under investigation, and more research is needed to develop effective therapies for this rare disorder.

The cause of systemic capillary leak syndrome is unknown, and there's no known cure. Treatment during episodes aims to stabilize symptoms and prevent severe complications. The use of intravenous fluids must be monitored carefully.

Monthly infusions of intravenous immunoglobulin (IVIG) can help prevent future episodes. Preventive treatment with certain oral medications originally designed to treat asthma also can be helpful, but these drugs may produce troublesome side effects, such as tremors.