If it's just skinny around the head and tail, and it's been that way since you got it, that's one thing. It may be just genetically mutated a bit and that's the way it is. If, on the other hand, this skinniness around it's head and tail is new, that's a problem.
If the condition is new, it signals that something is wrong. I have no idea what disease would cause that, and therefore no way to suggest treating it.
Here are the basics on clown loach care; they like to be in schools of at least 3 (5 is better), plenty of hidey places, and they tend to not do well being transferred from one tank to another. In my opinion, if you provide these three things, it should thrive, they're pretty hardy fish. If not, and this skinniness becomes worse, or more noticeable, my best advice is to take it out and not let it infect the others, or spread whatever unknown wasting disease it sounds like it has.
Good luck!