David Fajgenbaum was only 25 when he was hit by a rare and devastating illness.

A former quarterback at Georgetown, Fajgenbaum was known as the "Beast" for his incredible physique and stature. In July 2010, he had been studying at the University of Pennsylvania when he woke up one night with stabs of abdominal pain, and he was drenched in sweat.

During a visit to the emergency room, Fajgenbaum's doctor told him that his kidneys, liver, and bone marrow were not functioning properly. Moreover, his lymph nodes were swollen, red bumps appeared across his chest, and he felt exhausted all the time.

Doctors had no idea why his body was failing. Since then, finding out what medical condition ailed him had become Fajgenbaum's life mission. Needless to say, he took the matter into his own hands.

Afflicted By Devastating Symptoms

As Fajgenbaum's immune system went haywire, his body began to decline rapidly. His left eye became temporarily blind because of a retinal hemorrhage. He gained more than 70 pounds of extra fluid as his liver continued to fail. He got sicker and sicker.

Grant Mitchell, Fajgenbaum's former roommate, recalled that his friend's brain also began to slow down.

"I would ask him a simple question, and he would answer in a couple words, like 30 seconds to a minute later," Mitchell told the New York Times.

Doctors and students at Penn suspected that Fajgenbaum had cancer of the lymphatic system or lymphoma, while others thought it was a severe case of lupus or mononucleosis. However, all tests were inconclusive.

By September 2010, doctors gave Fajgenbaum steroids and his body began to fight back the disease. His liver and kidneys functioned properly again, and the extra fluid in his body receded. Fajgenbaum was released from the hospital.

But it took only a month for his symptoms to relapse, when he was staying at his childhood home in Raleigh, North Carolina. Doctors there sent a piece of Fajgenbaum's lymph node to pathologists at the Mayo Clinic, where it was finally identified as Castleman Disease. It was such a rare condition that doctors at Raleigh had no experience with it.

What Is Castleman Disease?

Castleman disease, which is also called angiofollicular lymph node hyperplasia or giant lymph node hyperplasia, involves the overgrowth of cells in the lymphatic system, the body's disease-fighting network.

As of writing, doctors have identified two types of this condition: localized Castleman disease and multicentric Castleman disease, which struck Fajgenbaum. Localized CD is the more common type of the illness and affects a single group of lymph nodes. This usually affects the abdomen and the chest. According to Mayo Clinic, localized CD is usually cured by removing affected lymph nodes through surgery.

On the other hand, multicentric CD affects more than one lymph node and can affect other organs that contain lymphoid tissue. It can sometimes affect people with human immunodeficiency virus (HIV). It is also linked to other cell-proliferation diseases, including lymphoma, POEMS syndrome, and Kaposi's sarcoma. Because of this, it's often difficult to distinguish multicentric CD and cancer.

MCD causes infections, fevers, fatigue, weight loss, nerve damage, and night sweats. It also weakens the body's immune system, making it difficult for the body to fight infections.

In the United States, only about 1,200 to 1,500 people have been diagnosed with multicentric CD. Studies have shown that only about 65 percent of people with the disease live for five years after diagnosis.

Search For Treatment

Over the next few years, Fajgenbaum alternated between periods of frightening relapses and relative health. His condition had been so severe that it stumped even those who were leading experts on the disease, including Dr. Frits van Rhee who has treated about 100 patients with Castleman.

Fajgenbaum used his own body as a test subject in the hopes of searching for a cure for this disease. In 2011, Dr. van Rhee acquired permission to treat Fajgenbaum with siltuximab, a drug being developed by Johnson & Johnson to treat patients with multicentric CD. At that time, siltuximab had not been approved by the Food and Drug Administration (FDA) yet, but it would be in 2014.

However, like other treatments, the drug did not work on Fajgenbaum.

With the zeal he once devoted to bench-pressing 375 pounds, Fajgenbaum decided to dive into scientific research on Castleman disease and familiarized himself with the world's experts. The more he learned, the more he realized that research on the disease was in disarray, he said.

Fajgenbaum called Dr. Thomas Uldrick from the National Cancer Institute to help him out with the research. He also began collaborating with Dr. van Rhee.

In 2013, Fajgenbaum earned his medical degree. He later entered the Wharton School, but by December 2013, he got sick again that his blood platelets dropped dangerously low. This time, he used his relapse to progress his search for the cure.

He collected weekly blood samples as "snapshots" of his immune system, organizing the results into a spreadsheet. When his disease returned, Fajgenbaum persuaded doctors to remove a piece of his lymph node and save it for research.

He received another round of chemotherapy and improved enough to work on his research. He found out that five months before he noticed symptoms coming back, the T cells in his body began to activate, preparing for a fight in his body's immune system arsenal. Three months before the relapse, Fajgenbaum noticed his body producing more of a protein that commands the body to create more blood vessels.

All these gave Fajgenbaum an idea: perhaps there was a problem with the communication lines in his body, particularly in the area that triggered the production of blood vessels and that activated the T cells. If he could shut down this communication line — known as mTOR pathway — he might be able to prevent a relapse. He prevailed.

In January 2014, Fajgenbaum started taking sirolimus or Rapamune, which is often given to kidney transplant patients. After a year, tests revealed that his immune system was returning to normal.

Fajgenbaum has started a nonprofit called Castleman Disease Collaborative Network to coordinate research on the disease. Now 31 years old, he is an assistant professor of medicine at Perelman School of Medicine.

"I didn't think that I would ever get to leave the hospital, and now here I am, fighting back," said Fajgenabaum. "It's the ultimate motivator."