Lichen planopilaris--It is a problem you need to deal with a dermatologist about, there are treatments. Talk to him/her to see if shaving you head might actually help the condition--as it does for psoriasis and similar skin problems. My bet is that the dr. will say that shaving won't hurt. You may want to consider an electric razor, at least at first until the patches are under control, a Cleanhead I think it is called is specially made for this. The hair on the back of the head is the most persistent even with the most developed mpb. Good luck, but I think Sly is your answer together with the ointments, etc. to control the inflamation.
making it seem worse than MPB since propecia won't even help one bit
If I don't use the guard, do I have the risk of cutting my scalp? Is the way you shave your head different vs having a guard?