My Brother Has Had A Skin Condition On His Hands

my brother has had a skin condition on his hands and arms for about a year now and we have not been able to get a conclusive diagnosis and have seen about 10 doctors in that time and no one has been able to figure this thing out yet. It appears on both hands and both arms from the elbows to the fingers and looks like blood blisters (without liquid caps) and very in size from1/8 inch to1 1/2 inch (some larger) they stay for a week or more then they seem to get a little better but don't go away, then come back even more numerous. He says they sting all the time. No doctor has photographed them, and have had NO diag. of this condition. Can you help me to figure out just what this can be??