I am the doctor who define DUPA (Diffuse Unpatterned Alopecia) in men. It is real and tragic when it happens. About half of the men respond to the drug finasteride, while others don’t respond to any medication and hair transplants are always contraindicated. Here is the article I wrote defining it: https://newhair.com/baldingblog/wp-content/uploads/pdf/mp-1997-evaluation.pdf
The diagnosis is made using a microscope to examine the hairs in the donor area of the back of the head. Miniaturization will significantly exceed 20%.