Refinance 2nd mortgage

[frugalQ]

Is it possible to refi a second mortgage only? Is it as simple as getting another HEL or a HELOC and rolling the existing HEL into it?

Are there different guidelines around a 2nd mortgage refi? Meaning does the cltv have to be lower than when you do a purchase money second?

I'm thinking that most lenders require 80% cltv when refi'ing, but would like to get input from the pros.