Kasabach Merritt Syndrome

Overview

Kasabach-Merritt syndrome is a rare condition that mostly affects babies. It happens when a large growth of blood vessels (a vascular tumour — a non-cancerous lump made of blood vessels) grows under the skin or inside the body and starts trapping platelets. Platelets are tiny cells in the blood that help it clot and stop bleeding. When platelets get caught inside the growth, the blood can't clot the way it should. This means the baby may bruise easily, bleed more than expected, and the lump itself may swell and grow. Doctors sometimes call it Kasabach-Merritt phenomenon. The growth is not the same as a common 'strawberry' birthmark (infantile haemangioma) — it is a different type of blood-vessel tumour, usually a kaposiform haemangioendothelioma or a tufted angioma.

No, it is very uncommon. Most general doctors will see very few cases, or none at all, in their whole career. Because it is rare, it is usually looked after by a specialist hospital team.

It almost always affects babies and young infants. It is often noticed at birth or in the first few weeks to months of life. It can affect boys and girls of any background. It is extremely rare in older children and adults.

Symptoms

Common symptoms

• A lump or swelling that may be firm, warm, and tender, and is growing quickly. It can appear on the trunk, arm, leg, neck, or deeper inside the body.
• Bruising that appears without any obvious injury, or bruising that spreads more than expected.
• Tiny flat red or purple dots on the skin (petechiae — little dots caused by blood leaking from tiny vessels).
• Bleeding that is slow to stop, for example from the nose, gums, or a small cut.
• Pale skin, tiredness, and poor feeding, which can be signs of anaemia (low red blood cells).

Symptoms in children

• Irritability, being floppy or unusually sleepy, or feeding less than usual.
• Pale skin, fast heartbeat, or fast breathing, which can be signs of anaemia.
• The lump getting bigger, harder, or shiny and stretched-looking.
• Being tender when the lump is touched or held.

Symptoms in older adults

• This condition is very rare after early childhood. When it does happen, signs are the same: bruising easily, bleeding that is hard to stop, and a growing blood-vessel lump.
• In older children or adults, the same blood tests and specialist assessment are used.

Causes

Main causes

• A blood-vessel tumour (a non-cancerous growth of blood vessels) that traps platelets inside it. Platelets are the small blood cells that help blood clot.
• Because platelets get used up inside the growth, the level of platelets in the blood drops (thrombocytopenia — a low platelet count).
• The growth also uses up clotting proteins in the blood, so the blood clots poorly and bleeding risk goes up.
• Doctors do not know exactly why these blood-vessel growths form. It is not caused by anything the parents did or did not do during pregnancy, and it is not usually passed down in families.

Risk factors

• Having a large blood-vessel tumour, especially one on the trunk, in the armpit, or deep inside the body.
• Being a baby in the first months of life.
• A bigger or deeper growth tends to carry a higher risk of clotting problems.

When to see a doctor

See a doctor urgently if:

• Your baby has new bruising without a cause, or tiny red or purple dots on the skin.
• A lump is growing quickly, or the skin over it looks shiny, stretched, or is breaking down.
• Bleeding is slow to stop.
• Your baby is pale, feeding poorly, very sleepy, or breathing fast.
• You already know your baby has this condition and any new bleeding or bruising appears.

Book a routine appointment if:

• You have questions about the diagnosis, treatment, or follow-up plan.
• You want to know what to watch for at home and when to call for help.
• You need advice about caring for the area around the lump, or about vaccines and everyday activities.

Diagnosis

A doctor will start by asking what you have noticed and when, then examine your baby and the lump carefully. Because this condition changes the blood, blood tests are the key step. Imaging scans help the team see how big the growth is and how deep it goes. Sometimes a small sample of tissue (a biopsy) is taken, but this is done carefully because of the bleeding risk.

Tests that may be done

• Full blood count — a blood test that counts platelets and red blood cells.
• Clotting tests — blood tests that check how well the blood clots and measure clotting proteins such as fibrinogen.
• Ultrasound scan — a painless scan using sound waves to look at the size and shape of the growth.
• MRI scan — a detailed picture of the growth and whether it reaches deeper tissues. Your baby may be given medicine to help them lie still and sleep during the scan.
• Sometimes a biopsy — a small tissue sample examined under a microscope to confirm the exact type of blood-vessel growth.

What to expect at your appointment

You may be seen by several specialists, often including a children's skin or blood-vessel team and a blood doctor (haematologist). Blood tests may be repeated often at first, because the team needs to track the platelet count and clotting. This can mean several appointments and some waiting. It is completely reasonable to ask who is leading your baby's care and who to contact if you are worried between visits.

Treatment

The aim of treatment is to shrink the blood-vessel growth, correct the clotting problem, and prevent serious bleeding. Babies with this condition are usually cared for by a specialist team in a children's hospital. Treatment is planned for your individual baby, and the team will explain the choices and the reasons behind them.

Self-care at home

• Keep every follow-up appointment, even if your baby seems well — blood tests are how the team spots problems early.
• Handle the area gently. Avoid tight clothing, rough play, and knocks to the lump.
• Learn to recognise the emergency signs and keep the contact details of your specialist team somewhere easy to find.
• Keep your baby's feeding and sleep routines as normal as possible; ask your team if you are worried about feeding.
• Ask your team before any procedure, including vaccinations, blood tests, or dental work, so they can advise on bleeding precautions.

Medical treatments

Doctors use treatments that aim to shrink the growth and settle the blood clotting. This can include medicines given by mouth or into a vein that slow the growth of the blood vessels, and sometimes a combination of treatments is used. Some babies need support for their blood, such as receiving platelets or clotting proteins through a drip while treatment takes effect. Babies with heavy bleeding or anaemia may need a blood transfusion. Pain relief and good nutrition are part of care too. Your specialist team will explain which approach suits your baby, along with the benefits and possible side effects — always ask them directly rather than relying on general information.

When is surgery considered?

Surgery is usually not the first choice, because the growth can bleed heavily and removing it completely is often difficult. It may be considered in selected cases, for example if the growth is small and in a place that is safe to operate on, or if other treatments are not working. Decisions like this are made by the full specialist team together with you.

Living with this condition

Early on, life may revolve around hospital visits, blood tests, and watching for bleeding. This can feel intense. Many families find it helps to keep a simple notebook of what they notice — new bruises, feeding changes, the size of the lump — and to bring it to appointments. As treatment takes effect and the growth shrinks, appointments usually become less frequent.

Lifestyle tips

• Choose soft, loose clothing and avoid anything that rubs on the lump.
• Supervise play closely, especially around sharp objects, stairs, and rough-and-tumble games, while the condition is active.
• Keep a small first-aid kit handy and know how to apply firm pressure to a bleeding spot.
• Ask your team about nursery, childcare, and travel plans so you can plan with confidence.
• Let anyone who cares for your baby — grandparents, childminders, nursery staff — know the warning signs and who to call.

Diet and exercise

Feed your baby as you normally would, and ask your team for advice if feeding becomes difficult or your baby seems very tired during feeds. Once the condition is under control, normal play and movement are encouraged and help your baby develop. Ask your specialist team before starting any contact sport or activity with a risk of knocks to the affected area.

Mental health and emotional wellbeing

It is normal to feel frightened, exhausted, or on edge when your baby has a rare condition. Some parents feel worried every time they see a small mark or a tearful night. Those feelings deserve attention too — you do not have to hold it all alone, and support is available. If low mood, anxiety, or sleeplessness is lasting, please speak to your doctor or midwife or health visitor, who can arrange support. If you ever have thoughts of harming yourself, contact your local emergency number or a crisis line in your country straight away.

Prevention

No, this condition cannot be prevented. It is not caused by anything a parent did or did not do, and there is nothing you could have done differently in pregnancy. What you can do is get help early if you notice a fast-growing lump, bruising, or unusual bleeding in a baby, because early treatment lowers the risk of serious problems.

Screening programmes

There is no routine screening test for this condition. Babies with a concerning blood-vessel growth are checked with blood tests and scans, and once a diagnosis is made, regular blood tests are used to watch the platelet count and clotting.

Complications

If left untreated

• Serious or hard-to-control bleeding, including bleeding into the gut, lungs, or brain.
• Severe anaemia from ongoing blood loss, causing tiredness, paleness, and fast heartbeat.
• The growth getting larger and pressing on nearby organs, which can cause breathing or feeding problems.
• Strain on the heart and circulation in severe cases.
• Pain and skin changes over the lump, and in some cases breakdown of the skin.

Long-term outlook

This is a serious condition, and it is honest to say that it needs specialist care and can be worrying for families. The encouraging news is that with modern specialist treatment, most babies improve: the growth usually shrinks over months to years and the blood clotting problems settle. Some children need longer follow-up, and a few have lasting effects from the growth or its treatment. Your specialist team can give you the clearest picture for your own child, and it is always fine to ask them what to expect next.

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