Amelioration
Not a word confined to medicine but a word used in medicine, amelioration is synonymous with improvement.
If a patient's condition shows amelioration, the patient is clearly better -- there is some improvement in her or his condition.
Amelioration infers that an effort is being made to correct or at least make more acceptable conditions that are difficult to endure.
The word 'amelioration' is compounded from the Latin 'ad',-', to or toward + ''melior', better = toward better = improvement.