Kasabach–Merritt syndrome

Overview

Kasabach–Merritt syndrome (KMS) is a rare and potentially life-threatening condition characterized by a vascular tumor (usually a kaposiform hemangioendothelioma or tufted angioma) associated with severe thrombocytopenia (low platelet count), microangiopathic hemolytic anemia, and consumptive coagulopathy. It typically presents in infancy and early childhood. The syndrome results in abnormal blood clotting and internal bleeding due to platelet trapping within the vascular tumor, leading to complications that require urgent medical attention.

Causes

The primary cause of Kasabach–Merritt syndrome is the presence of an aggressive vascular tumor, most commonly kaposiform hemangioendothelioma (KHE) or, less frequently, a tufted angioma. These tumors have an abnormal vascular structure that sequesters and destroys platelets and clotting factors, resulting in coagulopathy. The condition is not inherited and typically arises sporadically. The underlying reason why certain vascular tumors trigger KMS while others do not is not fully understood.

Symptoms

Clinical signs of Kasabach–Merritt syndrome are often dramatic and can include:

• A rapidly enlarging, firm, and purplish vascular mass (usually in the skin, soft tissue, or retroperitoneal area)

• Bruising and petechiae (small red or purple spots) due to low platelet counts

• Bleeding from the skin, gums, or gastrointestinal tract

• Signs of anemia such as pallor, fatigue, or rapid heartbeat

• Swelling or tenderness at the tumor site

The condition may present shortly after birth or within the first few months of life, though older infants and toddlers can also be affected.

Diagnosis

Diagnosis of Kasabach–Merritt syndrome involves both clinical evaluation and laboratory investigations. Key diagnostic steps include:

• Physical examination of the vascular lesion

• Blood tests showing severe thrombocytopenia, low fibrinogen, elevated D-dimer, and anemia

• Coagulation studies indicating a consumptive coagulopathy (disseminated intravascular coagulation-like profile)

• Imaging studies such as ultrasound, MRI, or CT scan to define the extent and nature of the vascular tumor

• Histological biopsy of the lesion, if needed, to confirm tumor type (e.g., kaposiform hemangioendothelioma)

Early recognition is critical to prevent serious bleeding complications and organ damage.

Treatment

Treatment of Kasabach–Merritt syndrome is complex and requires a multidisciplinary approach. Key treatment modalities include:

• Corticosteroids: Often the first-line treatment to reduce tumor size and inflammation

• Vincristine: A chemotherapeutic agent used in cases resistant to steroids

• Sirolimus: An mTOR inhibitor that has shown promising results in reducing tumor size and reversing coagulopathy

• Supportive care: Platelet transfusions, fresh frozen plasma, and cryoprecipitate may be needed in acute bleeding episodes

• Embolization or surgical resection: Considered in select cases where the tumor is accessible and not responding to medical therapy

Close monitoring of coagulation parameters and tumor progression is essential throughout treatment.

Prognosis

The prognosis of Kasabach–Merritt syndrome depends on early diagnosis, size and location of the vascular tumor, and response to treatment. With appropriate and timely medical therapy, many children recover well, though long-term follow-up is necessary to monitor for recurrence or complications. However, untreated or resistant cases can be fatal due to uncontrolled bleeding, organ failure, or tumor complications. Advances in targeted therapies like sirolimus have significantly improved outcomes in recent years.