I wash mine a couple times a year, have had one of them nearly a decade and no problems since. I do dry it till almost done, do not overdry, then I let it air dry the rest of the way and on top of that, dont use it for a couple days to make sure its good and dry. Do read the instructions, just in case yours is different.
I was thinking that putting it in the dryer would heat up the cords on the inside that make the blanket warm, and make them weaker (the casing around them), but was only just guessing. I'm a chicken butt and scared to use an electric blanket period.