Really wierd problem, has me stumped!

One of our stud cats, Tango, has a bald spots on both rear hocks in the exact same location and on his scrotum. The spots on the hocks are about "dime" sized and the scrotum spots are a bit smaller.
The spots are somewhat red, but not inflamed or weeping sores. They don't seem to bother him and he doesn't fuss at them. The hair is completely gone from these areas, so it looks very odd.
I have of course taken him to the vet and the diagnosis was indeterminate along with the cause and prognosis. A topical steroid was prescribed and has had zero effect. The symptoms remain the same and have not improved.
Ringworm has been ruled out completely.....whew!
Never the less, he still suffers from this and we have eliminated step by step anything that could be causing contact dermatitus, with no luck in solving the problem.
I'm not desperate for a solution, because he seems un-bothered by the condition, but it is ugly and visible and obviously not normal.
Anyone out there with suggestions or solutions for similar problems...I'm all ears and any help is appreciated!

Thanks!

Do cats get pattern baldness???

Do you think he might be allergic to his litter, that's all I can think of since it's his rear and the only thing that would be on his rear (well, and his paws but they're bald already) and not anywhere else.

I hope you find an answer!

Since it is on his hocks, maybe he got this from sitting?

If there is no reddness I would just watch it, and the hair should grow back. I would be careful of steroid use in a male cat used for breeding.

Crystal

TO FUNNY...Two of my cats are also missing hair(not on scrotum-just on the upper back legs. I brought it to vets attention just cause he was there for another issue and figured why not ask-he said it was ok-never saw it before but then again how many ppl would ask about it... I know its not ringworm here either as only 2/of 22 have it and they are brothers(were dumped at a day old and handraised also have their sister but she has her hair-it started thinning out at a year old-sometime after neuter. RJ

Could he maybe be over grooming himself in those areas?