Neurofibromatosis had completely devastated him.
I don't think that was the story they were telling because they never once mentioned to in TNT. They didn't even allude to it. In the original, when they did explain neurofibromitosis, it was explained as something that could cause death in infancy. If it was something that also caused mental deterioration, don't you think the doctor might have found that to be worth mentioning? Or that it would have been worth mentioning somewhere in the story of the series?
They could have used that as an explanation in TNT but they chose not to, which tells me that wasn't the intent of their story. They were showing a man who had lost every woman he was ever involved with, who had no real friends, and had spent his entire life consumed with bitterness. My interpretation of TNT's story was:
Let bitterness consume you and it will eventually turn you into a monster.
That's a better story to tell. How many of you have ever met anyone with neurofibromitosis? You can't relate to it. Everyone has known someone who allowed themselves to become bitter to some degree. The more bitter they let themselves become, the worse it usually affects them. That's very relatable to an audience.
We never got to see the progression of Cliff's mental state over the past twenty years. We saw him in the original as a bitter, vengeful, goofball and then 20 years later the whole transformation into a monster had already taken place.
We saw him transforming towards that in the original. He'd gotten to the point where the one person who had put up with him no matter what he did and always helped him and always loved him, Pam, finally needed one favor from Cliff. Just one favor.
Pam's greatest wish was to see the end of the Barnes-Ewing feud. She pleaded with Cliff to sell her his five percent of Ewing Oil. When it came right down to it, when Cliff had to make a decision between what mattered to him more - his love for his sister or his love for revenge - Pam lost. Cliff valued Pam less than he valued revenge. That was the next step towards Cliff transforming into a monster.
When TNT began, twenty years later, Cliff had already completed the rest of his transformation.