My husband has lost large patches of hair on his thighs and calves, it looks like laser treatment gone wrong.:-)What could cause something like that?

Alopecia. I am inferring from your question that he has not had a laser hair removal treatment. If he has loss a considerable amount of hair with no apparent logical reason, he should go to a dermatologist office for evaluation. Hope this helps.
Alopecia. He has a type of condition called alopecia, most likely. There are several different types, and these can by treated by a primary care or dermatology doctor.