hair loss

Our little Indy Mouse is about a year old. He's been treated for mites
in the past few months, with topical and oral medications. He had
experienced some hair loss during the treatment, and we thought it
would be growing back but it hasn't. The fur on his head is very
patchy. The skin underneath is nice and pink and healthy looking, and
he's not doing any excessive grooming or scratching. He's just patchy.
He's a white and black coat, and no other areas on his body are like
this. Is it just a permanent thing from the topical treatment? Is he a
balding middle aged mousie? Should we get him a toupe? *grin*

Any input is welcomed.

Joy