I've had my plant for 4 years and I recently started to notice that the stem of my plant have these marks on them and the leaves of my plant have been yellowing. I recently staked my plant but made sure to leave room around the wire and stem and even the plant stems that do not have wire have developed these marks. I may need to repot my plant and check the roots to see about the yellowing issue but I still don't understand the stems appearance.
Do you have a cat? It is curious that the marks on the dumb cane start out with small nicks at the top which become progressively larger as they go down; I mention a cat because cats think about gaining height and may be testing to see if they can climb on the plant or not. Note too that the stake has vertical slits - this might be just that the stake was put through a planer to make the surfaces smooth and the planer has a vigorous gripper which puts those marks in or there were nicks in the planer blades. If the nicks are consistent from bottom of the stake to the top then it is the planer's fault. Otherwise if the marks are concentrated about three feet up then might be a cat sized animal which still has claws testing the plant for climbability. Cats and Dieffenbachia do not mix well.
Dumb cane is pretty toxic to people and other animals and develops quite hard stems which thoroughly discourage insect interference except in the soft top growth. It is hard to imagine that the marks you see would be other than mechanical damage.
If the marks, which look as if they have self-repaired, get no worse and the yellow leaves are on the outside of the plant with the new growth healthy and bright green then I would not worry. As the plant gets bigger, yellow leaves might be a sign that it needs a more voluminous pot.