this is one of my dieffenbachia that has hit the ceiling more than once. so we cut the top off re-root it and plant it into another pot or if there is enough room it goes back intothe same pot to make it fuller.
This brings back memories...I remember going to the home of my music teacher (I took organ lessons.) when I was a kid...she had 2 of these and as a 9 year old I was blown away by how tall they were!