HLH: A Simple Description

In order to properly discuss or write about some of the more complicated aspects of this disease, I feel I need to try and post as simple an explanation of it as possible. It’s not as simple as I would like because it’s such a complicated set of problems, but I’ve tried to include the basic facts everyone interested should know.

Overview:

• HLH is a rare disorder of the immune system. It is also commonly referred to as a disease. It’s rarity is currently understood to be approximately 1 in 1 million children.
• There are two forms of the disease. The primary form is FHL, also known as Familial HLH. The secondary form is simply known as HLH. Both forms are treated in the same manner medically, with the exception of the additional need for a Bone Marrow or Stem Cell transplant to cure the primary form.

Description:

• When the body has an infection, certain specialized cells activate and fight off the infection. These cells are part of our Immune System. Among these cells are T-Cells and Histiocytes, which when activated cause an inflammatory reaction in the body.
• In most people when an infection(a cold, flu, other virus or a bacterial infection for example) has been eliminated, the inflammatory reaction that helps eliminate them is turned off and the Immune System returns to it’s “Steady State” or normal state. In HLH patients, the inflammatory reaction does not turn off and causes the symptoms of HLH.
• Our Bone Marrow produces our blood cells, including infection fighting cells. As the inflammation persists abnormally, the Histiocyte cells attack or “eat” the other blood cells in the bone marrow, causing a severe drop in cell counts. This means that the patient is exposed to normal infections, but has no way to fight those infections off.
• Typical symptoms of HLH itself can include: Fever, Pallor, Jaundice, Liver and Spleen enlargement, and Neurological symptoms such as irritability and seizures. Not all symptoms appear in all patients initially.
• Because symptoms vary widely and can be associated with other infections, HLH is very difficult to diagnose. It is an especially dangerous disease undiagnosed, with a fatality rate of 100% over a course of approximately 2 months. 100% of patients will die in 2 months if untreated.
• Patients have a better chance of survival of this disease the earlier they are diagnosed and treated. The longer the disease continues, the more damage the body does to itself. Because the treatment itself is hard on the body and the disease often affects young children, if the body is too badly damaged, recovery can be difficult even when treated properly.

Treatment:

• HLH is treated with a protocol or treatment program called HLH-2004. This program was created by an international team of doctors in 2004 to attempt to address the poor survival rates of patients with HLH. Prior to that point, a program known as HLH-94 was used.
• HLH-2004 involves a chemotherapy regimen (a set medicines given to the patient) to stop or suppress the inflammation in the body, bringing the disease under control.
• Once the disease is under control — once the immune system has “cooled off” — symptoms can begin to fade and the patient’s immediate danger from HLH itself is lessened. The patient is still at very high risk from normal infections due to the damaged immune system.
• Infection presents the greatest risk to patients with HLH after it has been diagnosed and treated.
• In the primary form of HLH, known as FHL, remission is only temporary. A Bone Marrow or Stem Cell transplantation is required for long term survival.
• In the secondary form of HLH, the disease can be permanently resolved with the HLH-2004 program in some cases.

More information is available at Histiocyte.org as a starting point. I’ve posted articles I’ve found to be useful in the Links section above as well.