What is Kasabach-Merritt Syndrome?
Kasabach-Merritt phenomenon (KMP) is a rare, potentially life-threatening blood disorder that typically affects newborns. Initially identified in 1940, this condition is characterized by a low platelet count (thrombocytopenia), a type of anemia where red blood cells are destroyed (microangiopathic hemolytic anemia), and excessive clotting (consumptive coagulopathy). These symptoms usually appear when there is a fast-growing blood vessel tumor. In particular, KMP is only seen in conjunction with certain types of tumors known as kaposiform hemangioendothelioma (KHE) and tufted angioma (TA), which are part of the same tumor category. Treatment for KMP involves supportive care as well as addressing the root cause, the underlying tumor.
What Causes Kasabach-Merritt Syndrome?
Kasabach-Merritt Phenomenon (KMP) only happens as a result of two rare, non-cancerous blood vessel tumors named Kaposiform Hemangioendothelioma (KHE) and Tufted Angioma (TA). These typically show up during infancy.
Despite being non-cancerous, KHE and TA are categorized as having an “intermediate malignant potential.” Meaning, these tumors have a tendency to grow and enter surrounding tissues quite aggressively but they aren’t known to spread to other parts of the body (a process known as metastasizing).
Risk Factors and Frequency for Kasabach-Merritt Syndrome
Kaposiform hemangioendothelioma (KHE) and Tufted angioma (TA) are rare conditions, with one study estimating their occurrence to be around 0.07 instances per 100,000 people. Despite this, KMP, a related condition, can affect up to 70% of people with KHE, and up to 10% of people with TA. These conditions can occur in people of any gender or ethnicity and usually appear in infants. The typical age of diagnosis is around 2 months. It’s quite rare for KHE to appear in adults, and when it does, it’s usually not associated with KMP.
- Kaposiform hemangioendothelioma (KHE) and Tufted angioma (TA) are rare, occurring in 0.07 of every 100,000 people according to one study.
- Kasabach-Merritt phenomenon (KMP), another related condition, can affect up to 70% of patients with KHE and 10% of patients with TA.
- These conditions can affect any gender or ethnicity.
- They typically start to show up in early infancy, and the average age of diagnosis is 2 months.
- It’s very rare for KHE to appear in adults, and when it does, it’s usually not related to KMP.
Signs and Symptoms of Kasabach-Merritt Syndrome
Kaposiform hemangioendothelioma (KHE) is a condition in which purple or reddish bumps appear on the skin or soft tissue. These bumps are firm and grow larger over time. They can have a rough texture and unclear boundaries. KHE can show up on the chest, arms, legs, or around the kidney area (retroperitoneum). Around one in ten cases do not involve the skin.
Another symptom is tufted angioma (TA), which is seen as a sequence of purplish spots and small bumps that often appear on the trunk. These spots and bumps can also be associated with excessive hair growth (hypertrichosis) or sweating (hyperhidrosis).
When KHE or TA is associated with Kasabach-Merritt phenomenon (KMP) in infants, the existing skin bump grows quickly and becomes tense, purple, or bruised. This can cause a lot of pain and dramatic swelling. It’s important to note that if the disorder is affecting the kidney area, the growth may not be immediately visible during physical examination.
- Purple or reddish bumps on the skin or soft tissue
- Bumps that are firm, grow larger, have a rough texture and unclear boundaries
- Appear on the chest, arms, legs, or around the kidney area
- Existence of purplish spots and small bumps that often appear on the trunk (TA)
- Excessive hair growth or sweating
- In infants with KMP, quick growth of existing bump, turning tense, purple, and causing pain and swelling
Testing for Kasabach-Merritt Syndrome
To diagnose KMP, which is a condition that affects your blood’s ability to clot properly, your doctor will need to do some lab tests and possibly identify if there’s an underlying vascular tumor, a type of blood vessel growth. These lab tests include a complete blood count to measure the number of different cells in your blood, a coagulation panel to check how your blood clots, and tests called PT (Prothrombin Time) and PTT (Partial Thromboplastin Time) to assess different aspects of blood clotting.
When these tests are performed, you may find that the number of platelets, the cells responsible for clotting, is very low. This is called thrombocytopenia. The PT and PTT tests may also show that your blood takes longer to clot than it should, and you may have low levels of fibrinogen, a protein that helps the blood to clot. Additionally, another test might show increased levels of a substance called D-dimer, which often indicates abnormal blood clotting processes.
The doctor will also need to identify the underlying cause, which often presents itself as a lesion on your skin. Usually, a physical examination can spot these lesions. However, if your doctor suspects a visceral tumor, which is a tumor inside your body, they may recommend an MRI scan. An MRI can help determine both the presence and the extent of a tumor. It can show increased contrast (gadolinium enhancement) and thickening of your skin and the tissue beneath it.
Biopsy, which is a procedure where a small sample of tissue is taken for testing, may be suggested to confirm what’s causing your symptoms. However, if KMP is already present, this may not be possible due to the risk of bleeding.
Treatment Options for Kasabach-Merritt Syndrome
KMP, or Kasabach-Merritt Phenomenon, is a condition associated with certain types of tumors. Its treatment mainly focusses on managing complications and treating the tumor causing KMP.
KMP patients often have low platelet counts, a condition known as thrombocytopenia. However, serious bleeding rarely occurs, and it’s typically not advisable to administer extra platelets unless there’s active bleeding. This is because the extra platelets can get stuck in the tumor, causing coagulation issues and exacerbating KMP.
If a patient with KMP develops anemia, which means they’ve lowered levels of red blood cells, it’s treated with a transfusion of these cells. In cases when there’s a risk of bleeding or prior to surgery, cryoprecipitate may be given. This type of treatment helps the blood to clot better.
Eliminating the tumor causing KMP is a vital part of the treatment. Surgery can be the definitive treatment for some of these tumors but often can’t be performed due to the invasive properties of the tumor or risk to local structures. Surgery might involve higher health risks once KMP occurs. If the tumor receives blood from a single blood vessel, it may be possible to close off that vessel in a process called embolization. However, these tumors often have multiple blood vessels supplying them, and embolization carries the risk of damaging surrounding tissues. Although radiation therapy can help shrink the tumor, it carries risks including developmental delay, growth delay, and secondary cancer development.
Several medications have shown promise in treating the types of tumors associated with KMP. Steroids are typically used as an initial treatment, with improvements usually seen within two weeks. After evidence of improvement, the steroid dose is typically decreased gradually. If drugs fail to shrink the tumor, other medications such as vincristine and mTOR inhibitors (like sirolimus) may be tried. Some expert guidelines recommend combining steroids with vincristine as a first-line therapy, recommending steroid treatment alone if vincristine is not readily available.
What else can Kasabach-Merritt Syndrome be?
There are various medical conditions that could cause certain symptoms or difficulties. Some of these include:
- Angiosarcoma
- Arteriovascular malformations
- Consumption coagulopathy
- Hemangioblastoma
- Hepatic hemangiomas
- Immune thrombocytopenic purpura
- Infantile hemangioma
- Teratoma
- Neuroblastoma
- Subcutaneous fat necrosis