How To Treat Thinning Of Hair In The Crown Area Due To Dandruff?

Hi, Am 36 years old and have always had an oily scalp with dandruff ever since my teens. Also hair on my head has always been thick & very fast growing.. Suffered from acne on face & had a dermatologist subscribe a course of Roacutane for 6-12 months when I was 21 years old as part of the treatment. Anyway last year I did’nt wash my hair for a bit (2-3months) and noticed an excess build up of thick dandruff near the crown area this finally prompted me to shampoo regularly - once a week using Head & Shoulders shampoo with a conditioner – but at the start of this year a friend noticed a noticeable thinning around the crown with much of the scalp clearly visible, almost the exact same area where the excessive build of dandruff was when I hadn’t washed my oily scalp for a 2-3 month period. Now my question is: Have I (that excess dandruff build up) done some permanent damage to hair follicles in that crown area? Will that 3-4 inch thin area near the crown ever recover to its former glory? FYI – rest of the hair is reasonable thick and grows fast & long as normal, but there is a visible thin patch near the crown surrounded by longer healthy hair. Cheers Baz