I pulled up the ISSA web site www.issaonline.com which would be the place for you to go to apply for any course through ISSA. Howver, I did not see a Pilates Rehabilitation course on their site. I am ISSA certified myself and am not aware that they offer a Pilates Rehab certification.
A very respected Pilates certification is Stott Pilates www.stottpilates.com, and they offer many specialty tracks.
I wish you good luck.