What is CM-TMA?

CM-TMA occurs when part of the immune system called the complement system becomes inadequately controlled. Excess complement activity can injure the endothelium, the cells that line blood vessels, and contribute to formation of microscopic blood clots.

This process may cause destruction of red blood cells (microangiopathic hemolytic anemia), a low platelet count (thrombocytopenia), and injury to organs. The kidneys are commonly affected, although CM-TMA can involve other organs as well.

What can trigger CM-TMA?

Some people may have an underlying susceptibility to complement dysregulation without symptoms until another stressor activates the system. Reported triggers and associated settings include:

• infection or significant illness
• pregnancy and the postpartum period
• surgery or major physiologic stress
• solid-organ or hematopoietic stem-cell transplantation
• severe hypertension
• autoimmune or inflammatory disease
• malignancy and certain medications

Because several conditions can produce a TMA picture, determining whether complement is the primary driver is an important part of the diagnostic evaluation.

What are the symptoms?

Symptoms vary depending on which organs are affected. Possible symptoms include:

How is CM-TMA diagnosed?

There is currently no single test that definitively diagnoses CM-TMA. Clinicians first determine whether there is evidence of thrombotic microangiopathy and then evaluate other potential causes.

How is CM-TMA treated?

Treatment is individualized based on disease severity, affected organs, possible triggers, and the patient’s overall clinical situation. Complement-inhibiting therapies have transformed care for many patients with complement-mediated disease.

C5 inhibitors such as eculizumab and ravulizumab are established complement-directed therapies for aHUS/CM-TMA. Other complement-targeted approaches continue to be studied. When CM-TMA is strongly suspected, treatment decisions may need to be made before genetic results are available.

How long complement inhibition should continue is an individualized decision based on disease course, recurrence risk, genetics, organ involvement, treatment response, and other clinical factors.

CM-TMA and the kidneys

Kidney involvement is common. Patients may develop acute kidney injury, protein or blood in the urine, high blood pressure, decreased kidney function, or need dialysis in severe cases. Some people recover substantial kidney function with treatment while others may have lasting chronic kidney disease. Care often involves both hematology and nephrology.

Is CM-TMA genetic?

Sometimes, but not always. Variants affecting genes involved in complement regulation can increase susceptibility to CM-TMA, but a disease-associated variant is not found in every patient. Having a variant also does not necessarily mean a person will develop disease.

Genetic counseling can help patients and families understand what results mean, whether relatives may benefit from testing, and possible implications for pregnancy or transplantation.

CM-TMA and pregnancy

Pregnancy and the postpartum period can act as triggers for complement-mediated TMA in susceptible individuals. Pregnancy-associated TMAs can overlap clinically with preeclampsia, HELLP syndrome, TTP, and CM-TMA, so evaluation may require collaboration among maternal-fetal medicine, hematology, nephrology, laboratory medicine, and genetics.

People with a history of CM-TMA who are considering pregnancy should discuss their individual risks and monitoring plan with an experienced multidisciplinary team.

CM-TMA, aHUS, or complement-mediated HUS?

Terminology continues to evolve. aHUS (atypical hemolytic uremic syndrome), CM-TMA (complement-mediated thrombotic microangiopathy), and complement-mediated HUS are overlapping terms that may be used differently across clinical and research settings. CM-TMA increasingly emphasizes the underlying complement-mediated mechanism.

Living with CM-TMA / aHUS

CM-TMA is not only an acute illness. Follow-up may include monitoring kidney function, blood pressure, blood counts, signs of hemolysis, treatment-related risks, recurrence, pregnancy planning, and genetic or family implications. Long-term care should be individualized to each person’s disease history and treatment plan.