As her physician assistant interviewed the patient, Kocharla carefully reviewed her records and test results. This kind of neuropathy was not uncommon in autoimmune disorders. Sjogren’s syndrome and lupus were probably the most common, but there were others. She would have to keep an open mind and look for other symptoms that might narrow the field. These kinds of mysteries were one of the great pleasures of working in rheumatology. The P.A. summarized her findings, and Kocharla entered the exam room and introduced herself to the middle-aged woman and her husband. She’d heard about the painful legs, Kocharla began, but what else has been going on? So much! She had aches and pains everywhere, and she’d lost more than 20 pounds over the past few months. Maybe the pain had stolen her appetite, but she hadn’t really felt well since she developed asthma two years earlier. That seemed to get the rheumatologist’s attention — which surprised the patient. She had told many doctors about her out-of-the-blue asthma, but none seemed to think it was important. Until now.

A New List of Symptoms

“Hang on a second,” Kocharla said, after hearing this part of the story. She turned to her laptop computer and typed something in it. Then she passed it to the patient. “Do any of these symptoms seem familiar?” she asked.

The patient looked through the list.

Fatigue: Sure, but who isn’t tired? Weight loss: check. Swollen lymph nodes: check. Muscle pain: check.

And she had the asthma and the numbness and weakness in her left foot and right big toe. “I think you have something called eosinophilic granulomatosis with polyangiitis,” Kocharla said. E.G.P.A. was formerly called Churg-Strauss syndrome for the two physicians, Jacob Churg and Lotte Strauss, who first described the condition in 1951. The disease is linked to an elevated level of white blood cells called eosinophils — the cells that respond in allergic reactions. Somehow these cells become involved in the destruction of small blood vessels all over the body. That’s what causes the numbness and the loss of strength and reflexes. These cells can lead an attack on blood vessels anywhere in the body. It is not clear what triggers this disorder, but it is a destructive, sometimes deadly, disease.

Kocharla checked the patient’s blood count. Indeed, her eosinophil count was quite high — eight times the level normally seen. The rheumatologist had never seen this disease in a patient before but had certainly learned about it in her fellowship. It would take a biopsy to confirm the diagnosis, but doing that could permanently damage the already-injured nerve. This patient fit nearly all the diagnostic criteria. She started the patient on a high dose of prednisone to weaken the white-cell-led attack. But because she had never seen a patient with E.G.P.A., she wanted the diagnosis confirmed by someone with more experience: She sent the patient to the Mayo Clinic in Rochester, Minn., to get a second opinion. Even before the patient saw the doctors at Mayo, she had no doubt that Kocharla had been right. After just a week on the steroids she felt great. The pain was gone. She could sit and stand. The level of eosinophils dropped to normal. She could go back to work. The rheumatologist at Mayo had seen many cases of E.G.P.A. before and agreed with Kocharla’s diagnosis. They started her on a second immune-suppressing medication.

Following her instincts as a reporter, the patient began to read up on the disease. One article suggested that walking can help control this and other autoimmune diseases, so the patient started taking walks. She averages six to seven miles a day. It has allowed her doctors to lower her medication doses, and she says that even though she is sick — in a very real way sicker than she has ever been — she has never felt healthier.

Lisa Sanders, M.D., is a contributing writer for the magazine. Her latest book is “Diagnosis: Solving the Most Baffling Medical Mysteries.” If you have a solved case to share, write her at Lisa.Sandersmdnyt@gmail.com.