One way you could do it is by placing the description field and the desc 1 field on top of each other and using the following formulas to suppress each one:
In the suppress formula for description, use-
isnull((table.item_key))
for the desc1 field suppress formula would be-
not isnull((table.item_key))
Make sure you have the suppress box checked and when the formula is entered, the equation icon will turn red.
I have used this technique in my reports. The idea being if the item key had data (not isnull) the desc1 will supress. If the item key does not have data (isnull), then the description will suppress. This way, one or the other will be visible, depending on the condition of the item_key.