As Gregory Maassen, Ph.D., prepares to e-bike more than 5,800 miles across the country, he's using the same sense of adventure and skills that he drew on for decades to guide economic development programs in countries throughout the world. It was during one of these international journeys — guiding hiking tours in South Africa on his free weekends — that he fell ill and soon experienced unexplained symptoms, which lasted for nearly two years.
After continuing to puzzle physicians, Maassen, a Dutch native who had studied, worked and lived in the United States, used an emergency green card to travel back to the country.
"I became weaker and weaker," says Maassen. During this period, he lost his voice, had acid reflux-like symptoms, and felt his body burn. "I got sicker and sicker," he says. "It was a slow but steady decline in my health."
Maassen had access to the best doctors in the world, but nobody could explain his symptoms. His internist recommended that he see a neurologist at Johns Hopkins Medicine, which led to a diagnosis of a postinfectious form of small fiber peripheral sensory neuropathy. This type of peripheral neuropathy, which accounts for a small number of cases, could be caused by a variety of factors, including being bitten by ticks, larvae or insects.
"I know what you have. I see it all the time," Maassen recalls Ahmet Hoke, M.D., Ph.D., director of the Merkin Peripheral Neuropathy and Nerve Regeneration (PNNR) Center, saying in response to an email that Maassen sent. Hoke told him to come to the center within a month for a skin biopsy to confirm it. "That was the turning point," says Maassen.
After receiving the diagnosis in April 2019, Maassen started treatment. He took a cocktail of four different medications, mostly to manage his pain. Then, he started exercising, which helps regenerate nerve fibers, suppresses pain and accelerates the healing process.
"I followed his advice," says Maassen. "I am now happy to say that I am off all medication."
"By two years, he was a changed man," said Hoke. "That approach had a big impact on him."
Hoke, whose research has been funded in part by the National Institutes of Health, explains that about 35 million U.S. adults age 40 and older, about 1 in 9, are affected by peripheral neuropathy, which damages the peripheral nervous system. "It's a silent epidemic," he says. "The incidence continues to go up because it affects older adults and people with underlying metabolic syndromes."
There are more than 100 types of peripheral neuropathy. Symptoms often follow damage that it causes to small or large nerve fibers. Common symptoms may include tingling, burning or numbness in the extremities, such as the hands and feet. Peripheral neuropathy from diabetes is the most common form. Other causes may result from being in a physical accident, receiving chemotherapy or having an underlying immune condition. Some are caused by mutations in our genes. Almost 1 in 3 cases have unknown origins.
One reason that Maassen's symptoms perplexed many doctors was that results from his nerve conduction tests, which assess the response of large nerve fibers, kept coming back fine. Since his neuropathy affects the endings of small nerve fibers that extend to the skin, he needed a skin biopsy. This test, which was first developed at Johns Hopkins in the 1990s and supported in part by federal research funding, assesses the health, function, and overall shape and size of sensory nerves.
Hoke explains that the type of neuropathy Maassen has can come on suddenly and damage the peripheral nerves. "After a couple of months, it stops and the body can slowly recover," he adds. This is when small nerve fiber regeneration takes place.
To support this process, Hoke prescribed Maassen medications to manage his pain as his nerves were trying to regenerate. Once Maassen started responding to medication and did well, Hoke recommended he start exercising.
"He told me I had to exercise," recalls Maassen. "I was thinking, are you out of your mind? This is crazy. How could I even think of exercising?"
However, he knew this was his last chance. "If I don't take it up, I don't know. What do you do?"
To start, Maassen, who had always been active, went for a bike ride. He compares the experience and his symptoms — which also included fatigue — to having a flu without a fever. He was tired. His body was sore and burning. Yet, he kept pedaling. He also found using an electric bike, or e-bike, was a way to exercise without having it "completely knock me out."
"I still had to push myself," says Maassen. "But I did. Slowly, over a period of 18 months or so, I got out of this nightmare. Exercise made a really big difference in my case."
That experience and journey has since launched many others. In December 2019, Maassen started an e-bike community in the Washington, D.C., area, which now has more than 1,500 members. Throughout this period, Maassen met many adults who use e-bikes to stay active while forging their own health journeys.
This includes a man who e-biked to and from chemotherapy sessions and men and women age 70 and older who e-bike to get outside and stay active.
Inspired by hearing from people throughout the country embarking on long e-bike rides, Maassen took his own cross-country journey.
After training for a year, Maassen departed from Washington, D.C., in 2022 for a 4,685-mile e-bike ride along the Lincoln Highway. During the trip, he braved every element: extreme heat, cold, flooding, storms and riding on terrain as flat as a pancake and as steep as desert mountains.
After four months, he ended in San Francisco and raised more than $178,000 to benefit people living with peripheral neuropathy. He also used the opportunity to raise awareness about the condition. That motivating force — increasing awareness and providing education — is why he's doing it all over again in 2026.
On March 1, Maassen will depart from West Palm Beach, Florida, on his e-bike and pedal more than 5,800 miles to Los Angeles. He will stop in several towns and cities along the way. These tour stops will enable him to connect with people living with the condition as well as doctors who may diagnose different types of neuropathy, including neurologists and neuromuscular specialists who are more likely to see people with uncommon and rare forms.
"Many patients don't know what they have," says Maassen. "The doctors don't know what they have." That is what he hopes to change.
Maassen and Hoke emphasize that this process starts with educating physicians and patients. They are focusing on raising awareness about different types of peripheral neuropathy that are uncommon and difficult to diagnose.
Hoke is also guiding different research initiatives at the Merkin PNNR Center, spanning from studies in the lab to clinical trials, to discover new treatment.
Right now, exercise is the only known way to regenerate nerve fibers. Some people, like Maassen, respond especially well. Other treatments focus on alleviating symptoms, which often includes pain. Throughout the next five to 15 years, Hoke remains hopeful that new treatments may emerge to stop nerve damage by preventing a final step in nerve degeneration. He is also hopeful that curative approaches may one day become available to people with certain subtypes.
One promising initiative Hoke's team has studied is how to inhibit an enzyme that serves as a last step in activating nerve degeneration. You could think of this drug inhibition as putting a sturdy piece of tape over a light switch to prevent anyone from flipping it on and lighting up the room. By studying how a drug could inhibit this enzyme, researchers are investigating how to keep the lights off and prevent the illuminating process that can lead nerve fibers to fray, come apart and atrophy, or become weak.
Another strategy investigators are studying is how to alter the course of the condition for people with inherited types of peripheral neuropathy. There are more than 100 different genes that can cause neuropathy, Hoke explains. As a result, investigators have been building scientific atlases of cells to understand the interactions that genes can have during a normal state of health and as nerves degenerate. By better understanding this, they will have greater insight into different therapeutic targets — which could come from new or existing drugs.
As an extension of this, the team is also studying new approaches with gene therapy.
For example, some people with inherited forms of peripheral neuropathy may produce too much or not enough of a protein to help support and protect their nerve fibers. Investigators are studying how different types of gene therapies could then be used to support a person having a functional copy of this gene or the right amount of the protein to restore their nerve health and function. These studies are also in the early stages of research.
Outside of identifying ways to alter the course of peripheral neuropathy, Hoke notes his lab is also studying how new treatment approaches could restore and regenerate nerve fibers.
Maassen, who has already raised more than $26,000 through his upcoming e-bike tour, supports it all. His main focus now, though, is to get the word out about the condition.
"I would like the term peripheral neuropathy to be known by anyone," he says. "I don't want anyone else to have to go through what I went through. That's the starting point."
Resources:
To learn about peripheral neuropathy, visit hopkinsmedicine.org/health/conditions-and-diseases/peripheral-neuropathy.
To learn about peripheral neuropathy research and the Merkin PNNR Center, visit hopkinsmedicine.org/neurology-neurosurgery/research/merkin-center.
