Originally Posted by Konnaha_yellow_flash
I do believe that Itachi's so called "disease" was nothing more then over use of sasanoo at this point in the manga. Tobi was BSing IMO.
The spitting up blood is a side effect of over using sasanoo which sasuke demonstrated himself against danzou. And, since itachi had a Invincible, Immortal Edo body. His MS jutsus side effects no longer phase him making the use of the MS in Edo state like a EMS. Because no matter how much Itachi uses his MS his eyes wont deteriorate any further. No matter how many time he uses amaterasu or tsukuyomi he won't be left vulnerable in pain. No matter how much itachi uses sasanoo. His body won't be effected making his "disease" null IMO.
Nagato was brought back in such a shit state as he was before he died because the syncing of Gedo Mazo must take its toll on the soul as much as the body IMO. Notice that once nagato got a portion of the hachibis chakra his body was revitalized.
But, if the state of the soul is what determines the state of the body then the spiritual energy of the hachibi must have revitalized his soul for his body to revitalize, right?
Pretty much that, yes.
Chakra is part spiritual energy, and part physical energy. Dojutsu seem to do better with spiritual energy, after all, that's what the Uchiha clan is supposed to have a lot of. This seems to indicate that that's what Nagato was drained of.