A 42-year-old man went to the hospital again and again with a high fever. Doctors thought it was a bad infection. But the fever kept coming back. His blood counts were low. His spleen and liver were swollen. It was a mystery.
This is a story about a rare condition that most people think only affects babies. But it can happen in adults, too. And it’s often missed.
Hemophagocytic lymphohistiocytosis, or HLH, is a serious problem with the immune system. Normally, your immune system attacks germs to keep you safe. In HLH, the immune system goes into overdrive. It attacks the body’s own healthy tissues. This can cause high fever, organ damage, and can be life-threatening.
HLH is very rare. It is most common in infants and young children. But this case shows it can also happen in adults. When it does, it’s often confused with a severe infection. This is because adults with HLH often have a virus or other infection at the same time. This makes it very hard for doctors to find the real cause.
For a long time, doctors thought primary HLH was only a childhood disease. Primary HLH is caused by a genetic mutation. It means the body’s immune system is born with a flaw.
Secondary HLH is different. It is triggered by an infection, cancer, or autoimmune disease. It is not caused by a genetic problem.
But here’s the twist. This case shows that an adult can have the genetic form of HLH, even if they also have a serious infection. In the past, doctors might have seen the infection and stopped looking. They would have called it secondary HLH. Now, we know that’s not always true. Doctors need to look deeper.
Think of the immune system like a fire department. When there’s a fire (an infection), the firefighters (immune cells) rush to the scene. They put out the fire. Then, they go back to the station.
In HLH, the alarm is stuck in the “on” position. The firefighters never stop. They keep rushing out. They don’t just attack the fire. They start breaking down the house itself. This is what happens in the body. The immune cells attack healthy organs.
The genetic mutations in HLH affect how these immune cells work. They are like a broken switch that can’t turn off. This study focused on a gene called UNC13D. This gene helps immune cells release signals to control the fire. When it’s mutated, the signals don’t work right. The fire rages out of control.
Researchers in China studied one 42-year-old man. He had a long history of fever and low blood counts. Doctors checked him for many things. They found he had a high level of the Epstein-Barr virus (EBV). They also found a fungal infection in his brain.
They used the standard HLH-2004 criteria to diagnose him. This is a checklist of symptoms and test results. He met the criteria. But they wanted to know why. Was it a secondary HLH caused by the infections? Or was it something more?
The man’s test results were very concerning. His ferritin level was extremely high (600 ng/mL). Ferritin is a protein that stores iron. A very high level is a red flag for HLH. His immune system was in overdrive.
His NK cell activity was only 3.57%. NK cells are like the body’s security guards. They kill infected cells. A normal level is much higher. This showed his security guards were not working.
Doctors also tested his genes. They looked at several HLH-related genes. They found a mutation in his UNC13D gene. This confirmed he had primary HLH. It was a genetic condition, not just a reaction to an infection.
After treatment with antiviral and antifungal medicine, his EBV levels went down. His symptoms improved. But the genetic cause was still there. It was the root of the problem.
This doesn’t mean this treatment is available yet.
This case highlights a critical point for doctors. When an adult has severe, recurring infections, it’s easy to blame the germs. But sometimes, the problem is inside the body’s own defense system. Genetic testing is key. It can tell the difference between primary and secondary HLH. This distinction is crucial for long-term treatment. It can also help other family members who might carry the same gene mutation.
If you or a loved one has had strange, recurring fevers and infections, talk to your doctor. Ask if HLH could be a possibility. This is especially true if standard treatments are not working. Genetic testing is not for everyone. But for some, it can provide a clear answer. It can explain why the body is acting this way. This case is a single report. It is not a final answer for all adults. But it opens the door for more awareness.
This is a case study of just one patient. It is not a large clinical trial. We cannot draw broad conclusions from one person’s experience. The findings need to be confirmed in more adults. More research is needed to understand how common this is.
Researchers are learning more about HLH in adults. The next step is to study more adult patients with similar symptoms. They need to see how often a genetic cause is found. This will help doctors create better guidelines for testing. For now, this case is a reminder to look beyond the obvious. Sometimes, the cause of a severe illness is written in our genes.