Hemophagocytic lymphohistiocytosis is a very rare disorder that can quickly become fatal, sometimes within weeks or days of its onset. It is characterized by extremely aggressive immune system activity, in which certain types of white blood cells attack and destroy healthy tissues in the body. The disease can be genetic or acquired, and it is usually seen in infancy or early childhood. Treatment options include immune system-suppressing drugs and chemotherapy to block the action of abnormal blood cells. In severe cases, patients may need to receive emergency bone marrow transplants.
The exact causes of hemophagocytic lymphohistiocytosis are not completely understood, but doctors have identified some risk factors. The genetic form of the disorder results from mutations in one or more specific genes that control the production and action of two types of blood cells: lymphocytes and histiocytes. The disease is autosomal recessive, which means that both parents must carry abnormal copies of the genes for their child to inherit it. The acquired form of hemophagocytic lymphohistiocytosis usually occurs after a severe viral or bacterial infection. The immune system fails to return to normal activity levels once the infectious pathogens have been eradicated from the body.
Lymphocytes and histiocytes normally help to fight off infections. In the case of hemophagocytic lymphohistiocytosis, however, the cells react to healthy body tissues in the same way that they do to pathogens. The result is organ inflammation, tissue death, and the destruction of important blood and bone marrow cells. Patients with the disorder commonly experience high fevers, skin rashes, and jaundice. The spleen, liver, and other organs can become enlarged and stop functioning properly. The brain may be affected as well, leading to irritability, mental confusion, seizures, and possibly coma or sudden death.
Doctors can diagnose hemophagocytic lymphohistiocytosis by carefully reviewing symptoms and performing a series of tests. Blood samples are analyzed to check for abnormal white and red blood cell counts and to screen for the presence of infections. Physical exams and imaging tests are useful in determining which organs have been damaged and to what degree. Patients who exhibit symptoms of hemophagocytic lymphohistiocytosis are hospitalized and treated right away.
The goal of treatment is to stop the over-activity of lymphocytes and histiocytes. Chemotherapy drugs and other immunosuppressants are often effective in temporarily shutting down most of the immune system, which gives organs and body tissues time to recover. The acquired form of the disorder is usually responsive to medical care, but most patients who have genetic conditions eventually need bone marrow transplants to prevent recurring problems. By removing abnormal cells from bone marrow and replacing them with healthy stem cells, a large number of patients are able to recover permanently.