it looks very similar to something I've got on one of my panda cories. He's got one side fin that's thickened and looks very similar to your photo. I don't know what it is, I've researched to try and find out but can find nothing much. There was some mention of some kind of 'fat lump' and this would seem to fit with what I can see.
What I can tell you is he's been like this for around 2 years. He's not affected by it, he swims normally, breeds with the females (and doesn't appear to pass it on) eats fine - no issues at all. It just looks horrible