If your "NA" will come from piped text, you can just generate the piped text string in another question (e.g., it might be ${e://Field/variable} for an embedded data field called variable), and then put that string as the fifth column header. Unfortunately you cannot hide the column with display logic.
There is a messier option that I am aware of. You can create two copies of this question, one without the fifth column, and one with the piped text for the fifth column. Then just use display logic to hide the question with the fifth column if the piped text will be "NA", and to show the one without the fifth column. The main issue here would be that your responses would be split between the two questions, and you would have to combine them via embedded data in survey flow to analyze all of the responses together. Doable, but messy.
I am sure there could be another way to solve it, but I would leave that to somebody else here :)