Trying to remember something I saw as a kid. Sci-Fi? Film or Episode?

Okay, this could be a little vague, but I'm trying to remember something I saw many years ago. I saw it in the early 90's on TV, but it could have been made earlier than that. It has been suggested before that it was maybe an episode of Amazing Stories, however I can't even remember whether it was a film, an episode or whatever...

OK. The ONLY thing I can recall is that a man became the host of some form of parasite or alien (possibly) that made him invulnerable to bodily harm.

There is one particular scene that I remember but I can't remember the exact details...

He went to see a specialist, and was either cut open for operation, or simply had an x-ray, and the doctors discovered that the 'parasite' had formed an extremely durable layer of bones(?) on the outside of his human bones (inbetween his skin and his bones). I vaguely remember seeing that there was no fleshy goodness between his ribs, and that his entire front torso had been covered up by this strange 'armor'.

Again, I'm sorry that it's so vague, but it's been about 20 years, so I honestly cannot remember anything else at all. I'm positive though, that I did not get to see the whole thing...

Anyway, I appreciate any efforts in helping me work this thing out!

cheers! and good luck :)