Could I have Alopecia Areata?

I am a 22 year old male living in New Zealand suffering diffuse thinning localized in the occipital region of my scalp. Dermatologist is stumped, he believes it could be alopecia areata but as the thinning is diffuse (uncharacteristic of AA) he is not able to provide a conclusive diagnosis. I will add that he noted my hairline and crown seem fine.

The diagnosis of alopecia reata is made by a biopsy of the scalp even if it is diffuse. This disease does not always present with a single bald spot and it can be a diffuse disease.