Word describing "Nothing Changed"

I'd first check if doctors have an accepted term for this. You want to use the established terminology of the subject area before you invent new terms. To use an example from another field, if I was writing a program to help editors mark up text, and I wanted to create a tool to allow an editor to say that another editor's mark-up should be ignored, I wouldn't call it "ignore" or "leave it alone", I'd call it "stet", because that's what editors call it.

I don't claim to know medical terminology, but just from what I've picked up casually, "stable" or "unresponsive" might be appropriate terms.

"Static" (or "statis") was the first word that came to my mind

I recommend unchanged, unless the doctors would prefer MetaEd's status quo ante (abbreviated SQA), in keeping with the opaque terminology they employ in their "scrips" (< prescriptions), their speech to each other, and sometimes even in their conversations with uncomprehending patients.

status quo ante or status quo are both clinically acceptable