The Collaborative International Dictionary of English v.0.48:

denigratory \denigratory\, a.
   same as denigrating.
   [PJC]

WordNet (r) 3.0 (2006):

denigratory
    adj 1: (used of statements) harmful and often untrue; tending to
           discredit or malign [syn: calumniatory, calumnious,
           defamatory, denigrative, denigrating,
           denigratory, libellous, libelous, slanderous]