This spring, Adam Tinnin, a normally healthy, active 16-year-old, experienced a viral infection that caused mouth sores, hives, then tingling and numbness in his feet. In a matter of days, he had no feeling in his feet and couldn't walk.

Adam went to the emergency room twice near his home in Sikeston MO, where doctors diagnosed a virus and sent him home with medication to treat the hives. When he lost the feeling in his feet, he and his mother, Stephanie, came to Washington University Medical Center to see specialists about his condition. He spent three weeks as an inpatient at St. Louis Children's Hospital undergoing dozens of tests, including nerve biopsies, a spinal tap and diabetes testing, which all were normal. Adam, frustrated and distressed, was preparing for discharge, worried that he might spend the rest of his life in a wheelchair.

"I felt like giving up," Adam says. "I would lie in my bed and cry and pray that someone would come along and figure out what was wrong. I felt that all hope was gone."

Susan E. Mackinnon, MD, the Sydney M. Jr. and Robert H. Shoenberg Professor of Surgery and chief of the Division of Plastic and Reconstructive Surgery, happened to be having lunch in the doctor's lounge at the hospital on a day when Adam's case was being discussed. Mackinnon's interest was piqued, and she asked if she could examine Adam.

After the examination, Mackinnon was confident she knew what Adam's trouble was — a neuropathy with tarsal tunnel syndrome, similar to carpal tunnel syndrome, but in the ankles.

To diagnose tarsal tunnel syndrome, also called posterior tibial neuralgia, Mackinnon uses a test she developed with a colleague that she calls the "scratch-collapse" test. Adam's test was positive for irritation of his tibial nerve at the tarsal tunnels.

"I scratched along the tibial nerve and his arms collapsed, indicating a problem with that nerve," Mackinnon says.

Tarsal tunnel syndrome, which can be difficult to diagnose, is caused by pressure on the tibial nerve, which follows a long route down the back of the leg to the ankle, where it turns and curls below the inside of the ankle. Sometimes ligaments and other tissues that surround the nerve press on it, causing pain, a burning sensation and tingling on the sole of the foot. In Adam's case, it also caused paralysis and prevented him from walking.

Mackinnon says she believes a prior ankle sprain made him susceptible to the development of this acute tarsal tunnel.

"While tarsal tunnel syndrome is not a rare condition, it is very uncommon that it becomes so severe that a patient can't walk, especially in someone so young," she says.

Mackinnon performed tarsal tunnel release surgery on Adam's left foot this past May. During the one-hour procedure, she cut the covering over the tibial nerve to relieve the pressure.

Everyone has some covering over the nerve, but Adam's was very thick. By the time he had the surgery on his right foot in June, he had some feeling back in his left foot and was able to drive and walk with crutches. The severe pain in his left foot was gone.

Problems are indicated if a scratch along the tibial nerve causes a patient's arms to collapse. Susan E. Mackinnon, MD, performs the "scratch-collapse" test on patient Adam Tinnin.

By late June, he had feeling back in his toes and could walk without assistance. About a month after the second surgery, he returned to his job at UPS and was back to being a normal, healthy teenager.

Adam, who is just starting his junior year of high school, plans to use the experience to fuel his drive to become a physician, with strong leanings toward anesthesiology or plastic surgery. He also would like to attend Washington University as an undergraduate in two years.

"I took for granted what I had before, but when everything was swept out from underneath me, I knew then that anything can be taken away from us," Adam says.

The son of a pastor and the oldest of five children, Adam says the experience has changed him for the better and made him a more spiritual person.

"Now when I see people in wheelchairs, in my spirit I begin praying for them because I know how it is and what it's like to be there," he says.

And Adam says he is very grateful to Mackinnon for taking the time to care and for changing his life.

"I believe Dr. Mackinnon was sent by God into my room that day, and I know I will never forget her."