On the relation of dystonic movements to serum thyroxine levels.

A patient with psychomotor retardation secondary to delayed treatment of cretinism developed abnormal dystonic movements in the absence of other signs of toxicity during levothyroxine replacement therapy at a serum thyroxine level of 16 mug./100 ml. The dystonic movements disappeared when the serum thyroxine level fell. The abnormal movements were considered to be related to high thyroxine levels in this patient with pre-existing central nervous system dysfunction.