TAMPAHeather Glenday is used to discomfort. A competitive swimmer since childhood, Glenday, now 21, swims for the University of Tampa. She has had to push past being tired and achy to train and win at national events.But a year ago, she had unusual pain on her right side that persisted even in the off season. One day, she awoke and found she could barely bend her right arm, which had swollen to about three times the size of her left. Doctors at Tampa General Hospital found a blood clot in her upper arm, just below her collar bone."I got really upset," said Glenday, an accounting major in her junior year at UT. "It was like a ticking time bomb in my body."Blood clots often form in the legs, frequently in people who are sedentary. But Glenday's clot was another thing entirely. "It's a rare condition, but it's very strongly associated with athletes and exertion," said professor of surgery and director of the division of vascular surgery at USF Health, Dr. Karl Illig. "I've treated professional baseball players, swimmers, badminton players, painters, kayakers, even a professional guitarist and a professional violinist." Effort thrombosis is also known as Paget-Schroetter syndrome after the men who identified it in the 1800s. Repetitive, strenuous arm movement damages a large vein between the collarbone and the top of the rib cage. The bones and other structures in that area repeatedly squeeze the vein, causing blood to stagnate and creating enough irritation in the vein walls for a clot to form. The condition usually affects young, healthy individuals; more men than women; and tends to occur in the dominant arm. Football, rugby and tennis players, golfers, weight lifters, cheerleaders, backpackers, and rowers have also been diagnosed with the condition. It frequently is misdiagnosed, because it's so unusual for a blood clot to occur in a healthy young person, and particularly rare in the arm.But, if diagnosed promptly and treated properly, athletes can usually return to their sport. "The worst thing you can do is treat it like a blood clot in the leg," said Illig, who heads one of a handful of clinics across the country that specialize in treating effort thrombosis. A clot in the leg is usually treated with blood thinners, which isn't always enough to resolve effort thrombosis. "That results in disability in a quarter to half the people. It can also leave you with a swollen, achy arm for the rest of your life," he said.The recommended treatment is a clot dissolving drug, often delivered directly to the center of the clot, and surgical removal of the first rib. That's a small bone at the top of the rib cage, one Illig says "you won't miss.''The two-pronged approach relieves pressure on the vein and prevents clots from reforming. "That leaves patients with a 95 to 100 percent chance for a normal life," said Illig, who did Glenday's surgery at Tampa General.It's a condition that comes on gradually. During the 2011-12 school year, Glenday's right side bothered her almost daily, an early sign that the vein in her upper arm was being compressed. She thought it was just another sports-related issue and ignored it. The clot most likely formed in early spring 2012 after heavy training for a national competition.After she was admitted to TGH in April 2012, Glenday was put on blood thinners and a week later had surgery to remove her first rib bone.She missed three weeks of school but was able to finish her class work while recovering at home in Babylon, N.Y. She was back in the pool in a month, worked as a lifeguard that summer on a Long Island beach, and by fall she was back in Tampa, ready to train and compete.Illig said the key to that kind of a happy outcome is getting proper treatment quickly. Wait too long and the clot may solidify so much that it can't be dissolved. Also, there is a small risk that a piece of the clot could get to the lungs or brain resulting in a stroke or death. A more likely consequence of delaying treatment is chronic arm pain or disability. "If Heather had ignored the swelling and discomfort, she wouldn't have been able to return to swimming competitively," said Illig, who sees two to three new patients a month with this condition. "It's curable if treated correctly. It's not just another blood clot in your leg."