Hughes, who had been complaining of numbness in his right arm, may be suffering from thoracic outlet syndrome, Yankees manager Joe Girardi said after Wednesday night's 3-1 victory over the White Sox.
"We can't tell you that he has it or doesn't have it right now," Girardi said. "I think any time you talk about circulation problems, there's some concern. There's always a concern."
According to the website for the National Institute of Neurological Disorders, thoracic outlet syndrome is an umbrella term that encompasses three related syndromes that cause pain in the arm, shoulder and neck. Treatment for the syndrome can be as simple as physical therapy or can involve surgery.
The specialist whom Hughes will consult, Robert William Thompson, is a vascular surgeon. The Yankees did not say when Hughes is traveling to St. Louis or when they expected him to rejoin the team.
Hughes was at the Stadium after Wednesday night's game, but a public relations person said he would not be coming out to talk to reporters. The usually gregarious Hughes did talk to reporters before the game, and before he had found out the results of the tests, and seemed anxious to find out what had been causing him arm problems.
"I'm ready to figure out what it is, fix it and get back to throwing," Hughes said. "I hope it's not something that sets me back too much. Hopefully, it's something minor and fixable and something that will get me back to being what I know I can be."
The 24-year-old was placed on the disabled list on April 15 with what the team originally described as a dead arm. In addition to numbness and pain, he had been experiencing a marked drop in the velocity of his fastball. Hughes is 0-1 with a 13.94 ERA.
Hughes was named to the American League All-Star team last season, when he was 18-8 with a 4.18 ERA. However, he struggled in the second half of 2010, going 7-6 with a 4.90 ERA after closing the first half 11-2 with a 3.65 ERA. He logged a career-high 1761/3 regular-season innings in 2010.
He had been scheduled to make a rehab start Thursday, but then he had a setback after throwing 20 pitches during a bullpen session Monday afternoon.