I had the same thing for 20 years.
I just "cured" it....at least I think so.
I went to the dermatologist and just told him to cut it out. He did it and then had it sent for analysis. They came back with "some type of Psorasis".
After the surgery he gave me a spray on topical antiseptic called Merfin.
I used it every day after the surgery.
It came back again after the surgery but slightly off of the place it was for 20 years. It was not as big though as it had benn for those 20 years.
I got lazy about using Merfin but them began seeing that it seemed to get better when I sprayed Merfin on in the morning after my shower.
I then saw progress of sure and kept using the Merfin once a day...3-4 sprays on the spot.
They poof! It is gone. I still feel where it was and it is feeling like a normal part of my scalp now...
First time in 20 years.
There is something in this Merfin stuff and it seems to be some type of an tough infection that I could not sure with anti viral drugs, antibiotics (almost every varety), tar shampoos, topical antibiotics, lancing the center with a needle (tried myself out of frustration)....
The Merfin stuff did the trip. 20 years of that damn thing and now it is looking like it is gone for good.
I hope this helps.