Hemophagocytic lymphohistiocytosis (HLH) is a rare immune system disease. It occurs more often in babies and young children. But it can also occur in adults. Children may inherit the disease through genes. This is called familial HLH. But in adults, many conditions can cause HLH. This is called acquired HLH. It can be caused by some infections, cancer, and autoimmune diseases.

If you have acquired HLH, your body's immune system does not work normally. Some white blood cells called histiocytes and lymphocytes attack your other blood cells. Abnormal blood cells then build up in your spleen and liver. This causes your spleen and liver to enlarge. HLH is a life-threatening condition. It can cause death in weeks or months if not treated. It may also cause death in months despite treatment.

HEE-moh-FAY-goh-SIHT-ihk

LIHM-foh-HIHST-ee-oh-sih-TOH-sihs

HLH is a rare disease, and researchers are still learning what causes it. There are two types of HLH: familial and acquired. Familial HLH is passed from parents to children. Acquired HLH in adults can be caused by:

• Viral infections, most often Epstein-Barr virus.
• Other infections from bacteria or fungi.
• Some types of cancer, such as T-cell lymphoma.
• Autoimmune diseases.
• Medicines that suppress the immune system.

If your acquired HLH is caused by a virus, you may have another genetic disease called X-linked lymphoproliferative disease.

You are more at risk for acquired HLH if you have any of the following:

• Epstein-Barr virus
• Cancer
• Autoimmune disease
• Taking medicine to suppress the immune system

The most common symptoms of acquired HLH are:

• Fever.
• Enlarged spleen.

Other symptoms can include:

• Enlarged liver.
• Swollen lymph nodes.
• Skin rash.
• Yellow color of your skin and eyes (jaundice).
• Lung problems, such as coughing and trouble breathing.
• Digestive problems, such as stomachache, vomiting, and diarrhea.
• Nervous system problems, such as headaches, trouble walking, vision disturbances, and weakness.

The symptoms of acquired HLH can look like other health conditions. See your doctor for a diagnosis.

Your doctor will ask about your symptoms and health history. The doctor may also ask about your family's health history. They will give you a physical exam. The physical exam may include feeling your belly where your liver and spleen are. You will also have blood tests. These are done to look for:

• Low levels of white blood cells called natural killer cells.
• Low levels of other white blood cells, red blood cells, and platelets.
• High levels of fats in your blood called triglycerides.
• Low levels of fibrinogen, a protein needed for clotting.
• High levels of ferritin, a protein that stores iron.
• High levels of a specialized protein called sCD25, which increases in your blood when your immune system is stimulated.
• Signs of infection.

You will also have genetic testing and a bone marrow biopsy. Bone marrow is soft tissue in the center of some large bones. Blood cells are made in bone marrow. For this test, a sample of your bone marrow is taken with a needle. The tissue is looked at in a lab with a microscope.

Treatment will depend on your symptoms, your age, and your general health. It will also depend on how severe the condition is.

Acquired HLH may go away when your doctor finds and treats the cause, such as an infection. In other cases, more treatment is needed. Treatment for acquired HLH that doesn't go away may include:

• Cancer medicines (chemotherapy).
• Medicines that affect your immune system (immunotherapy).
• Medicines that fight inflammation (steroids).
• Antibiotic medicines.
• Antiviral medicines.
• Blood transfusion.

If medicine treatments don't work, your doctor may do a stem cell transplant. In this procedure, you are given high doses of chemotherapy or radiation to wipe out your diseased bone marrow cells that are then replaced by healthy bone marrow cells from a donor. Stem cell transplant carries risks and side effects but may be an effective treatment for HLH.

Talk with your doctor about the risks, benefits, and possible side effects of all treatments.

HLH is a life-threatening condition. It can cause death in weeks or months if not treated. It may also cause death in months even with treatment.

Researchers don't know how to prevent acquired HLH.

Contact your doctor now or seek immediate medical care if:

• You have symptoms that don't get better, or get worse.
• You have new symptoms.

• Hemophagocytic lymphohistiocytosis (HLH) is a rare disease of the immune system. It occurs more often in babies and young children. But it can also occur in adults.
• In adults, many conditions can cause HLH. This is known as acquired HLH. It can be caused by some infections, cancer, and autoimmune diseases.
• If you have acquired HLH, your body's immune system does not work normally. Abnormal blood cells build up in your spleen and liver. This causes your spleen and liver to enlarge.
• The most common symptoms of acquired HLH are ongoing fever and enlarged spleen.
• You will have blood tests and may also have a bone marrow biopsy.
• Acquired HLH may go away when your doctor finds and treats the cause, such as an infection. In other cases, more treatment is needed.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new directions your doctor gives you.
• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions, especially after office hours and on weekends and holidays.