Cat is looosing hair on back legs?

This can be quite a common occurrence in cats. There is a name for this condition & I cannot bring the Word to my mind right now. It is due to a thyroid disorder most of the time. It is not called mange. Mange is caused by a mange mite, either the sarcoptic or demodex mite and this is not the condition the cat has. You do need to take your cat into your Veterinarian to have it checked though and he will do the necessary blood tests & treat with the appropriate medications.