The 65-year-old man collapsed into the driver’s seat of his car in a small town outside Philadelphia. He could hear his breath: ragged, wheezy and fast, interrupted by a relentless cough. Winter was always bad for his breathing, but that year had been particularly hard, and that morning felt more difficult than usual. Just walking from his house to his car left him gasping for air as if he had sprinted the short distance.

He didn’t bother using an inhaler. The many lung doctors he had seen over the years all said he had “atypical” asthma because the usual medications never helped. When his breathing got really bad, his doctors would give him a couple of weeks of prednisone. Maybe it was time for another round of steroids, he thought as he sat in his car. After a few minutes of concentrating on his breathing, he felt well enough to make the drive to work.

He’d had these episodes of wheezing, cough and shortness of breath for as long as he could remember. When he was young, he would have a spell maybe once every couple of years. For the past decade or so, it seemed as if these attacks would come on every winter. But recently he felt short of breath all year round. He might feel better for a week or two, but the wheezing and cough always came back. He had seen doctors from Philadelphia to Boston over the years, and they all told him he was a mystery they just couldn’t solve — words no one wants to hear. He was a research scientist for a company in Philadelphia, and he loved his job, but his asthma was making it hard for him to work. His wife might be right; maybe it was time for him to retire.

At his office building, the man made his way toward his lab. If he walked slowly enough, he could avoid triggering the wheeze and cough. On the way, he stopped at the office of an old friend, Karen Sims. She was a doctor, though not his doctor. He knew she loved tough cases. She had told him it was one of the things she missed the most since leaving clinical practice for research.

She greeted him cheerfully. After they exchanged pleasantries, he told her: “I’m having trouble with my breathing.” Tell me about it, she said. He described his symptoms and how they had progressively grown worse: wheezing, shortness of breath with the slightest exertion and this gut-wrenching cough. The symptoms were worse in cold weather and when he lay down flat.

Does anything come up when you cough? she asked. Yes. It was odd; he usually coughed up mucus, but sometimes, mixed in, were these funny filaments. They were milky white and firm and smooth like plastic. And they often looked like the branches of a tiny tree. After he coughed up the solid stuff, he felt better, but it usually didn’t last more than a day or two. And then it started all over again.

That is strange, his friend agreed. She said she would think about this. Almost as soon as he was out of her office, she turned to her computer. The branchlike substance he coughed up reminded her of the blood clots removed from patients’ lungs that sometimes retained the shape of the branching blood vessels they came from. Casts, they were called. But clots weren’t white.

She searched the terms wheezing, cough and bronchial casts. The very first search brought up references to something she had never heard of: plastic bronchitis. It is a rare and sometimes life-threatening disorder that involves the lymphatic system. Normally lymph comes from the interstitial tissues of the body. This fluid collects in the delicate vessels of the lymphatic system, flowing through the infection-fighting tissues of the lymph nodes and eventually returning to the bloodstream, connecting with a vein just above the heart.

In plastic bronchitis, the lymph fluid leaks into the airways deep in the lungs, a place it would usually never go. Once there, the liquid solidifies, obstructing the flow and exchange of oxygen. When these dried plugs are coughed up, they can retain the shape of the airways they once blocked.

Plastic bronchitis is most common in children who have surgery to correct certain structural problems in the heart. But it can also be seen in adults, either after heart surgery or in a handful of disease processes, particularly inflammatory diseases of the lungs, like cystic fibrosis or severe allergic reactions.

When Sims reported her findings to her friend, she acknowledged that she wasn’t sure what caused his plastic bronchitis — if that’s what it was. She’d heard about a doctor at the University of Pennsylvania, in Philadelphia, who was familiar with the rare disease. He should see Dr. John Hansen-Flaschen. He might be the doctor who could finally figure this out.

Hansen-Flaschen is an emeritus professor of medicine at Penn, which means he is years past the usual retirement age. He primarily sees patients with diseases that others have not been able to diagnose. The doctor spent two hours with the man, getting every detail of his story. On examination, the patient was wheezing, and at the base of each lung, he could hear a crackling noise, like the sound made when Bubble Wrap is crushed. Hansen-Flaschen, like Sims, thought that the man probably did have plastic bronchitis. The question was why. He had never had surgery on his heart. And he didn’t really fit the pattern for many of the other diseases. It sounded as if he’d had this all his life.

Hansen-Flaschen postulated that the man could have been born with some abnormality in his lymphatic system — a narrowing or blockage that caused the lymph fluid to back up and overflow into his lungs. He had seen this disorder only a few times, but he had been fascinated by these patients and by the handful of other similar cases he’d read about.

Hansen-Flaschen knew an interventional radiologist at Penn, Maxim Itkin, who had developed a way to visualize the lymphatic system. By injecting contrast dye into the lymph vessels, he would be able to see any leaks or blockages in the system.

The patient went to see Itkin a few weeks later. Using an ultrasound probe, the doctor located the lymph nodes in the man’s groin. He then injected contrast dye into the nodes. He used a type of X-ray known as fluoroscopy to follow the dyed lymph as it traveled through the abdomen into the chest. Sure enough, he could see the fluid leak into the lungs. And at the very top of the lymphatic system in the chest, where the contents were supposed to be flushed into the blood stream, the vessel was narrowed and nearly completely obstructed.

The increased pressure caused by the obstructed vessel had opened many tiny leaks into the lungs and chest. Itkin injected a type of glue into the network of vessels, blocking all lymph flow up into the chest. It would increase the pressure in the lymphatic system in the abdomen and pelvis, but any overflow or leakage there would not cause life-threatening symptoms.

The effect was almost immediate. Within days, the coughing and mucus production stopped completely, and the patient was no longer short of breath.

Itkin and Hansen-Flaschen think that the man was most likely born with a kink in his lymph tubing that created the problem in the first place. This kind of lymphatic system abnormality used to be considered a rare disorder, but since Itkin and his team developed this new way to image the lymphatic system, he has seen enough cases to think that it is more common than was previously considered. “New tests reveal new diseases,” Itkin told me.

As for the patient, it has been three years since his procedure, and he feels great. He’s 68 now. He still loves his work; he’s still not ready to retire.