The New England Journal of Medicine Downloaded from nejm.org on May 27, 2014. For personal use only. No other uses without permission.
Copyright © 1994 Massachusetts Medical Society. All rights reserved.
The New England Journal of Medicine Downloaded from nejm.org on May 27, 2014. For personal use only. No other uses without permission.
Copyright © 1994 Massachusetts Medical Society. All rights reserved.
The New England Journal of Medicine Downloaded from nejm.org on May 27, 2014. For personal use only. No other uses without permission.
Copyright © 1994 Massachusetts Medical Society. All rights reserved.
The New England Journal of Medicine Downloaded from nejm.org on May 27, 2014. For personal use only. No other uses without permission.
Copyright © 1994 Massachusetts Medical Society. All rights reserved.
The New England Journal of Medicine Downloaded from nejm.org on May 27, 2014. For personal use only. No other uses without permission.
Copyright © 1994 Massachusetts Medical Society. All rights reserved.
The New England Journal of Medicine Downloaded from nejm.org on May 27, 2014. For personal use only. No other uses without permission.
Copyright © 1994 Massachusetts Medical Society. All rights reserved.
The New England Journal of Medicine Downloaded from nejm.org on May 27, 2014. For personal use only. No other uses without permission.
Copyright © 1994 Massachusetts Medical Society. All rights reserved.