Section 22. Modification of awards, decisions or orders

Upon its own motion
  or  upon  the  application  of any party in interest, on the ground of a
  change in conditions or proof of erroneous wage rate, the board  may  at
  any time, subject to the limitations set forth in sections twenty-five-a
  and  one  hundred  and  twenty-three  of this chapter, review any award,
  decision or order and,  on  such  review,  may  make  an  award  ending,
  diminishing  or  increasing the compensation previously awarded, subject
  to  the  maximum  or  minimum  provided  in  this  chapter,  and   shall
  immediately  send  to  the  parties  a copy of its decision, which shall
  include a statement of the facts which formed the basis of  its  action.
  No  such  review  shall  affect such award as regards any moneys already
  paid, except that an award increasing the compensation rate may be  made
  effective  from  date  of  injury,  and  except  that if any part of the
  compensation due or to become due is unpaid,  an  award  decreasing  the
  compensation rate may be made effective from the date of injury, and any
  payments  made  prior  thereto in excess of such decreased rate shall be
  deducted from any unpaid  compensation,  in  such  manner  and  by  such
  methods as may be determined by the board.