▁International ▁Head ache ▁Society ' s ▁International ▁Classification ▁of ▁Head ache ▁Dis orders ▁( IC HD ), ▁which ▁published ▁the ▁second ▁edition ▁in ▁ 2 0 0 4 . ▁The ▁third ▁edition ▁of ▁the ▁International ▁Head ache ▁Classification ▁was ▁published ▁in ▁ 2 0 1 3 ▁in ▁a ▁beta ▁version ▁ahead ▁of ▁the ▁final ▁version . ▁This ▁classification ▁is ▁accepted ▁by ▁the ▁W HO . ▁ ▁Other ▁classification ▁systems ▁exist . ▁ ▁One ▁of ▁the ▁first ▁published ▁attempts ▁was ▁in ▁ 1 9 5 1 . ▁The ▁US ▁National ▁Instit utes ▁of ▁Health ▁developed ▁a ▁classification ▁system ▁in ▁ 1 9 6 2 . ▁ ▁I CH D - 2 ▁▁ ▁The ▁International ▁Classification ▁of ▁Head ache ▁Dis orders ▁( IC HD ) ▁is ▁an ▁in - depth ▁hier arch ical ▁classification ▁of ▁head aches ▁published ▁by ▁the ▁International ▁Head ache ▁Society . ▁It ▁contains ▁explicit ▁( oper ational ) ▁di agnostic ▁criteria ▁for ▁head ache ▁dis orders . ▁The ▁first ▁version ▁of ▁the ▁classification , ▁I CH D - 1 , ▁was ▁published ▁in ▁ 1 9 8 8 . ▁The ▁current ▁revision , ▁I CH D - 2 , ▁was ▁published ▁in ▁ 2 0 0 4 . ▁ ▁The ▁classification ▁uses ▁numeric ▁codes . ▁The ▁top , ▁one - digit ▁di agnostic ▁level ▁includes ▁ 1 4 ▁head ache ▁groups . ▁The ▁first ▁four ▁of ▁these ▁are ▁class ified ▁as ▁primary ▁head aches , ▁groups ▁ 5 - 1 2 ▁as ▁secondary ▁head aches , ▁c ran ial ▁neural gia