Use a corticosteroid to get the sh*t under control, and use a shampoo like Nizoral to maintain. I have to use Nizoral 2% every day (I usually only expose the scalp for 1 minute) to avoid an outbreak.
I had untreated scalp SD for many years. The doctor prescribed me Diprosalic, and my scalp was good for several months. Then it came back, and I developed contact dermatitis towards Diprosalic... But, try it.