Kasabach-Merritt phenomenon

Kasabach-Merritt phenomenon (KMP), also known as Kasabach-Merritt syndrome, is a life-threatening condition characterized by a rapidly enlarging vascular tumor associated with profound thrombocytopenia (very low platelet count) and consumptive coagulopathy (a bleeding disorder caused by excessive clotting within the tumor). It is not associated with common infantile hemangiomas but rather occurs specifically in the context of kaposiform hemangioendothelioma (KHE) or tufted angioma (TA), which are rare vascular tumors. The condition primarily affects infants and young children, though it can occasionally present at birth or rarely in older individuals. The underlying mechanism involves platelet trapping within the abnormal vasculature of the tumor, leading to severe thrombocytopenia, low fibrinogen levels, and elevated D-dimers — a state known as localized intravascular coagulopathy. This can result in widespread bruising, petechiae (small red or purple spots on the skin), bleeding complications, and potentially fatal hemorrhage or organ failure. The vascular tumors most commonly occur in the skin and soft tissues of the extremities, trunk, or retroperitoneum, and they may grow rapidly, causing significant swelling, pain, and a purplish discoloration of the overlying skin. Treatment of Kasabach-Merritt phenomenon requires urgent intervention and typically involves a combination of pharmacological therapies. Sirolimus (an mTOR inhibitor) has emerged as a first-line medical therapy and has shown significant efficacy in shrinking the tumor and correcting the coagulopathy. Other treatments include vincristine, corticosteroids, and antiplatelet agents such as aspirin and ticlopidine. Platelet transfusions are generally avoided unless there is active life-threatening bleeding, as transfused platelets may be trapped within the tumor and worsen the condition. In refractory cases, surgical resection or embolization may be considered. Despite advances in treatment, KMP carries significant morbidity and a reported mortality rate that has historically been as high as 20-30%, though outcomes have improved with modern therapeutic approaches.

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