Kasabach-Merritt Syndrome

Kasabach-Merritt syndrome (KMS) is a rare complication of either of two benign (noncancerous) tumors that can affect infants. They are kaposiform hemangioendothelioma (KHE) and tufted angioma (TA). They’re vascular tumors. This means they’re made of blood vessels.

About 7 out of 10 babies born with KHE and 1 out of 10 born with TA develop KMS. Without treatment, it can cause severe bleeding that can be fatal. This is because with KMS, the tumors lead to:

• Low platelets: This makes it hard for blood to form clots.
• Low clotting proteins: Not having enough clotting proteins can also interfere with clotting. KMS can lead to low levels of the clotting protein fibrinogen.
• Low red blood cells (anemia): Anemia deprives the body’s cells of oxygen.

It’s also called Kasabach-Merritt phenomenon (KMP). If your baby has it, their healthcare provider will start treatment ASAP to keep them safe.

Symptoms of Kasabach-Merritt syndrome

This condition can lead to symptoms of anemia, like fatigue, and bleeding that doesn’t stop. But the most obvious signs parents notice first are tumors. The tumors are usually under your child’s skin on their arms, legs, trunk, neck or face. Signs include:

• A large, growing reddish or purplish mass with poorly defined borders
• Darkened or reddened areas of skin that look like raised, scaly patches
• Lesions that appear bruised or splotchy, with small red or purple spots

In about 1 in 10 babies, the tumors form inside a body cavity or organ, so you can’t see them. 

The tumors often hurt, so your child may be fussy or irritable.

Kasabach-Merritt syndrome causes

KMS happens when a kaposiform hemangioendothelioma or a tufted angioma causes problems with bleeding and clotting.

The tumor traps platelets and (sometimes) red blood cells. The odd blood vessels within the tumor can damage the red blood cells traveling inside. This causes them to die too soon.

Meanwhile, tiny clots form inside the blood vessels. They use up clotting proteins, like fibrinogen.

This can leave your baby with too few platelets and clotting proteins. As a result, their bodies may be unable to stop the bleeding if they’re injured. KMS can lead to low red blood cells (anemia).

How doctors diagnose this condition

Doctors diagnose most children before they’re a year old. They’ll assess visible tumors. Your child will likely need imaging to see if the tumor extends into tissues inside their body. These tumors don’t spread, but they can damage nearby tissue.

They’ll need a blood test to check for abnormal blood cell counts and clotting issues. Tests may include:

• Complete blood count (CBC)
• Partial thromboplastin time (PTT)
• Prothrombin time (PT) test
• Fibrinogen test
• D-dimer test

How is it treated?

Treatment focuses on preventing bleeding issues and getting rid of the tumor. KMS is so rare that there’s no single standard treatment that doctors agree on for everyone. Instead, your child’s healthcare provider will tailor treatment based on your child’s situation.

Medications

Several medications can treat KMS. They include:

• Sirolimus: This medicine starves the tumor of the nutrients it needs to survive. Your child may take it with or without a steroid.
• Vincristine: This chemotherapy drug may be an option if sirolimus doesn’t help enough. It destroys tumors. But it can also cause side effects that your child’s provider will discuss with you.

Procedures

Medical procedures include:

• Surgery: Removing the tumor may be an option if it’s small. Since the tumors are made of blood vessels — which pose bleeding risks — surgery isn’t the best option in all cases.
• Embolization: This procedure blocks blood vessels supplying nutrients to the tumor. This may be a good option if only a few blood vessels are feeding a tumor.
• Radiation therapy: Radiation can shrink tumors. But it can cause unpleasant side effects and increase your child’s risk of cancer in adulthood. Still, it may be the best option if other treatments aren’t helping enough.

Supportive care

Your child may need blood components if they’re at risk of major blood loss. They may need them if they’re injured. Or their providers may give them this treatment before surgeries or procedures that pose bleeding risks. Treatments include:

• Blood transfusions
• Platelet transfusions
• Cyroprecipitate
• Fresh frozen plasma

When should I see my healthcare provider?

Your child’s healthcare provider will monitor them closely throughout treatment. They’ll check their blood cell counts and clotting proteins.

In the meantime, seek emergency care if your child is bleeding. In addition to blood loss that’s visible, be aware of the signs of internal bleeding, including:

• Irregular heartbeat
• Slow reflexes or movement
• Trouble breathing

What can I expect if my child has this condition?

The mortality rate for Kasabach-Merritt syndrome is 30%. This means that it’s fatal for 3 in 10 babies who have it. The outlook tends to be worse for babies without visible tumors. Often, they don’t get diagnosed until their condition has become more serious.

New medicines for KMS, like sirolimus, are helping more children with KMS survive. Platelets usually start to increase within a matter of days after treatment starts. Clotting proteins usually start to increase after a few weeks.

Treatment usually continues until the tumor resolves or your child is no longer at risk of bleeding or clotting issues.

Is there anything I can do to feel better?

One of the best things you can do for your child is to work with healthcare providers with experience treating these rare tumors.

Medical experts are still studying the best treatments for Kasabach-Merritt syndrome. There’s still lots to learn about the long-term effects of treatment.

This is why working with experienced medical professionals provides the best outlook for your child.