Yankees starting pitcher Phil Hughes sits in the dugout during...

Yankees starting pitcher Phil Hughes sits in the dugout during Monday's loss to the White Sox at Yankee Stadium. Hughes suffered a setback during a bullpen session earlier in the day. (Apr. 25, 2011) Credit: AP

General manager Brian Cashman wanted to make it clear: The Yankees don't know if Phil Hughes has the daunting-sounding thoracic outlet syndrome. But if he does, it will not be good news for the 24-year-old righthander.

Cashman announced Thursday night that Hughes, who is on the disabled list with mysterious weakness in his shoulder, will travel to St. Louis on Monday to meet with Dr. Robert William Thompson, a vascular specialist based at Washington University.

If Dr. Thompson concludes that Hughes has thoracic outlet syndrome, the treatment could include surgery, Cashman said, and that could cost Hughes the rest of the season.

"It'd be a long-term thing," Cashman said. "I've heard basically, typically, that if that's what it is, a surgery would have to be involved and I would suspect it would be the season. I haven't asked. I just know that from previous players who have had it, it's not something that 'here, take some aspirin and shut it down for a week.' It's not that."

Pitchers who have been treated for the syndrome include Aaron Cook of the Rockies, Matt Harrison of the Rangers, Jeremy Bonderman (formerly of the Tigers) and Noah Lowry (formerly of the Giants).

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.

But there's a chance Hughes doesn't have it, which is what the Yankees are hoping for -- even though it still would leave them with no answer to to why Hughes' fastball has disappeared. Cashman equated the Yankees' search for the cause to the TV show "House," in which a cantankerous doctor solves medical mysteries.

"If you've ever watched the show 'House,' where you peel the onion, you're trying to find out," he said. "It's not like a situation where you have someone that says, 'This hurts.' It's more of you're trying to come up with clinical diagnoses based on a lot of information."

(For people who haven't seen "House," Cashman said: "It's a good show. You should watch it.")

Manager Joe Girardi revealed the possible diagnosis after Wednesday's game. Hughes has not spoken to the media since that information was revealed. "Phil's mood -- he's one of those guys where his mood doesn't change much from day to day," Girardi said. "To me, his mood seemed par for the course."

Hughes, an 18-game winner in 2010, is 0-1 with a 13.94 ERA in three starts. His rotation spot has been taken by Bartolo Colon, who has pitched well.

Another veteran option, righthander Kevin Millwood, pitched for Triple-A Scranton/Wilkes-Barre against Charlotte Thursday night. He didn't last long, allowing six runs in two innings. It was the final outing for Millwood before an out clause in his contract; if the Yankees don't call him up by Sunday, Millwood can become a free agent. Cashman wouldn't tip his hand either way. Millwood could agree to extend the deadline.

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