I would probably recommend testing for MS, but mareks may also be a cause. It's so hard to know for sure without testing. Take a look at this link with pictures, then click on "gross lesions" and look at the first 10 pictures for skin lesions: http://partnersah.vet.cornell.edu/avian-atlas/search/disease/502
Mareks disease lymphomas in leg

Mareks disease lymphomas in leg