A case history was a detailed description of a particular patient's experience with a specific medical condition.
In 2151, Doctor Phlox asked Esaak for copies of lab work and case histories of Valakians in every stage of their disease, which he agreed to provide. (ENT: "Dear Doctor")
In 2368, Dr. Beverly Crusher asked Dr. Toby Russell whether she had reviewed an injured Worf's case history yet, to which Russell replied that she had only looked at it briefly. (TNG: "Ethics")