The hospital scene and the final scene
I realize that the novel the story was drawn from was published in the early 1960s, but I don't know how much of the film's hospital scene and the final scene were taken from the novel.
There's a bit of a similarity between what happens in those scenes and what happens in the film version of Myra Breckinridge (1970), the screenplay for which was written between the writing of the novel The Tenant and the production of the film version of The Tenant.