All forms of loshon hara are prohibited even when the information is true and accurate. (Only in very specific circumstances is it permissible to say something that would otherwise be considered loshon hara).
Slander, referred to as hotzaas shem ra (spreading a bad name), is worse loshon hara which is derogatory but true.
To relate derogatory information that is essentially true but includes either exaggerations or even slight altering of facts is considered hotzaas shem ra.
Sefer Chofetz Chaim, 1 Cheshvan, page 110