spasmodic contractions of the neck muscles

hi guys, couple of weeks back we got a case in our pain clinic, he was on some kind of psychotic drug( therapeutic, prescribed by the physician), he developed spamodic contractions of his neck muscles, especially the trapezius and the sterno cleido mastoid muscles, initially he was injected with lignocaine in his, sternal fibres, he found some relief, we thought that blocking the nerve at the entry point in to the muscle would help him, this week we found him with even more worse spasmodic contractions, i suggested use of icing to desensitize the part and to everyones surprise up on a compression at the myofascial trigger points( as mentioned in Travel and Simons, ) the spasmodic contrations came down to less than 30%, and on icing it became nil, but as soon the cooling faded off the contractions started again, can some body give me suggestions on how to go about this case, thanks.