The Collaborative International Dictionary of English v.0.48:

Sibbens \Sib"bens\, n. [Etymol. uncertain.] (Med.)
   A contagious disease, endemic in Scotland, resembling the
   yaws. It is marked by ulceration of the throat and nose and
   by pustules and soft fungous excrescences upon the surface of
   the body. In the Orkneys the name is applied to the itch.
   [Written also sivvens.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sivvens \Siv"vens\, n. (Med.)
   See Sibbens.
   [1913 Webster]