Kasabach-Merritt Phenomenon

Kasabach-Merritt phenomenon is a rare, life-threatening condition in which either of two specific vascular tumors (tufted angioma or kaposiform hemangioendothelioma) traps and destroys platelets, which are a component of blood that helps clotting. This condition is also associated with other abnormal clotting conditions in which there is excessive consumption of clotting factors.

Kasabach-Merritt phenomenon does not occur in children with infantile hemangiomas. Tumors usually occur shortly after birth and are equally common in males and females. These tumors can involve any area of the body but most commonly involve the extremities and chest. They are usually associated with skin changes. In the area of the lesions, the skin appears firm, warm, and purple.Tumors also can involve internal organs and can be serious when they occur deep within the retroperitoneum (abdomen).

As the tumor grows, it causes more platelet trapping. This is associated with abnormal clotting and utilization of clotting proteins, creating a deficiency in these proteins. Because of this, bleeding can occur and can be fatal.

Children with Kasabach-Merritt phenomenon are initially hospitalized and monitored until they are stable. No single treatment approach is effective and unfortunately, responses to various treatments are inconsistent.

Initially, corticosteroids such as prednisolone are given at varying doses. If this approach is not effective, chemotherapy with vincristine (a drug widely used to treat cancers) is started. If this regimen is not effective, other drugs such as interferon, Cytoxan, and Amicar are used.

When the tumor does not respond to drug therapy, embolization (a highly specialized procedure in which particles are injected into the blood vessels to stop the blood flow), surgical removal, or both may be necessary. Blood products such as platelets and packed red blood cells are administered only if absolutely necessary.

KMS has a mortality rate of about 30%. For patients that survive the acute disease, supportive care may be required through a gradual recovery. The lesion may take many years to decrease in size. Studies suggest that some patients have residual lesions even 10 years after diagnosis. Improvement in platelet counts initially occurs with a decrease in the size of the lesion.

Patients may need care from a dermatologist or plastic surgeon for residual cosmetic lesions. On long-term followup, most patients have skin discoloration and/or mild disfiguration from the dormant tumor.