What is HLH?
Hemophagocytic Lymphohistiocytosis (HLH) is a rare, life threatening immune system disease affecting people of all ages and ethnic groups. It is caused by an overactive, inflammatory response and tissue destruction due to abnormal immune system reaction.
The immune system is a complex network of cells, tissues, organs and proteins that work together to keep the body healthy. In HLH, the immune system responds to a stimulus or “trigger," often an infection, but the response is ineffective or abnormal. This abnormal response causes a variety of symptoms which, if not treated, can be life threatening. HLH is dangerously aggressive in its progression and attack on vital organs.
Pronunciation
HEE-moh-FA-goh-SIH-tik LIM-foh-HIS-tee-oh-sy-TOH-sis
Common Symptoms
- Fevers
- Enlarged spleen
- Low blood counts
- Liver abnormalities
- Neurologic problems
- Respiratory distress syndrome (ARDS) often resulting in multiple organ failure
The Two Major Types of HLH
- Familial (Primary HLH) - This type is inherited, meaning it can be passed down from generation to generation.
- Acquired (Secondary HLH) - Doctors currently do not believe this type is inherited. Instead, it is thought to result from a reaction to specific infections, cancers and autoimmune disorders. Sometimes they cannot detect any trigger. This type usually occurs in older children and adults. Doctors do not completely understand why certain people develop acquired HLH.
Diagnosing HLH
HLH is difficult to diagnose. Given its rarity, many doctors and medical staff have never encountered an actual case. Additionally, HLH presents with symptoms common to many different disorders and conditions. The only definite way to diagnose HLH is through extensive blood work, genetic testing and bone marrow biopsy analysis. Left untreated, the prognosis of HLH is poor and generally fatal. Mortality in secondary HLH has been reported to vary from 8–22% in rheumatological HLH to 18–24% in EBV HLH.
The key to improving outcomes for HLH patients is swift diagnosis and research, and thus spreading awareness of the disease is important. If we teach more emergency department doctors, family practitioners and pediatricians about how HLH presents in its early stages, we can save more lives. Most of the time HLH is diagnosed after all other options have been exhausted or it is misdiagnosed, thus losing valuable treatment time. It can take several weeks or months for diagnosis, if ever diagnosed at all.